Gen Chem 1
Which compound requires more oxygen to combust: Propane, propanol, or propanoic acid? How do we figure this out?
*+1 for each Carbon atom -0.5 for each Oxygen atom* Highest number = Requires most oxygen to combust Propane: +3 - 0 = 3 Propanol: +3 - 0.5 = 2.5 Propanoic acid: +3 - (0.5*2) = +3 - 1 = 2 propane > propanol > propanoic acid
- How will increasing the concentration of reactants affect the reaction rate? - How will decreasing the concentration of reactants affect the reaction rate?
- *If the reactant whose concentration you're increasing is included in the rate law*, then increasing the concentration/amount of reactant will increase the likelihood that the reactants will encounter each other, collide, and react. This will increase the reaction rate. - *If the reactant whose concentration you're decreasing is included in the rate law*, then decreasing the concentration of that reactant will decrease the likelihood that the reactants will encounter each other and collide to start a reaction. This will decrease the reaction rate.
A chemist prepares a solution by adding 200mL of 0.80M Fe₂(SO₄)₃ to 2.0 L of water. How many moles of sulfate ions are present? a) 1.6 x 10⁻¹ b) 4.8 x 10⁻¹ c) 4.8 x 10² d) 1.6 x 10²
- Answer = b) 4.8 x 10⁻¹ moles of sulfate ions Need moles of SO₄²⁻ → Get from moles of Fe₂(SO₄)₃ *2.0 L of water is irrelevant, because we're looking for moles of sulfate, not moles of water. 200 mL = 200 x 10⁻³L = 2.0 x 10⁻¹L 2.0 x 10⁻¹L Fe₂(SO₄)₃*(0.80mol Fe₂(SO₄)₃/L) = (2.0 x 10⁻¹L * 8.0 x 10⁻¹mol/L) = 16.0 x 10⁻² mol Fe₂(SO₄)₃ 16.0 x 10⁻² mol Fe₂(SO₄)₃*(3 moles SO₄²⁻/mol Fe₂(SO₄)₃) = 48.0 x 10⁻² moles sulfate = 0.48 moles sulfate a) 1.6 x 10⁻¹ b) 4.8 x 10⁻¹ c) 4.8 x 10² d) 1.6 x 10² Answer = b
- How will increasing the pressure affect the reaction rate? - How will decreasing the pressure affect the reaction rate?
- Pressure is a measure of the amount of force caused by the random movements of molecules over a specific area, and so if you increase the pressure, you increase the likelihood that the reactant molecules will collide with each other, and this will increase the reaction rate. - Decreasing the pressure will decrease the possibility of reactants colliding with each other, so the reaction rate will decrease.
-What is a rate law, and how is it determined? -How do you find the overall order of a reaction with multiple reactants?
- The rate law = the rate at which reactants are being consumed. Units = Molarity/s. • Only deals with first few seconds of reaction (when [reactants] and [catalysts] are both high) • Rate can only be determined experimentally, through empirical observation of data to figure out the order of each reactant separately • Neither rate laws, nor the study of kinetics in general is at all concerned with products. It depends completely upon reactants. • Rate Law for a Single Reactant: Rate = k[A]^m • k = rate constant • Only certain reactants included in rate law • m = reaction order Rate law for a reaction with multiple reactants: Rate = k[A]^m*[B]^n*[C]^o... - To find the overall order of a reaction, count up all the exponents (orders) for each reactant.
second quantum number
- house - orbital shape - each type of house has its own unique shape - l - determine using first quantum number: l = 0→(n-1) - s orbitals = 0 - p orbitals = 1 - d orbitals = 2 - f orbitals = 3 - s orbitals are 3d, sphere-shaped around the nucleus - p orbitals are dumbbell-shaped, and oriented across either x axis, y-axis, or z-axis
third quantum number
- room - magnetic quantum number - ml - orientation of orbital around the nucleus - determine using second quantum number - ml = -l → +l - total # of mls = total # of orientations possible
first quantum number
- street address - aka principle quantum number - n - highest energy level - valence shell - determine by looking at periodic table:
fourth quantum number
- twin - spin quantum number - ms - mnemonic: twin/spin - each electron wants to share a room with its twin - one twin = +1/2 - other twin = -1/2
Draw an energy diagram for a two-step reaction with a slow step and a fast step.
-Step 1: Smaller activation energy = fast step - Step 2: Larger activation energy = slow step
A compound is found to contain 50.05 % sulfur and 49.95 % oxygen by weight. 1) What is the empirical formula for this compound? 2) The molecular weight for this compound is 64.07 g/mol. What is the molecular formula for this compound?
1) Assume a 100 g sample 50.05% S → 50.05 g S 49.95 % O → 49.95 g O 50.05 g S*(1 mol S/32.06 g S) = 1.56 mol S 49.95 g O * (1 mol O/16 g O) = 3.12 mol O 1.56 mol S/1.56 = 1 mol S 3.12 mol O/1.56 = 2 mol O Empirical Formula = SO₂ 2) Calculate empirical weight: 1(32.06) * 2(16.00) = 32 g + 32 g = 64.00 g Divide the molecular weight by the empirical weight: 4. 64.07 g/64.00g = 1 Multiplier = 1 (SO₂) * (₁) = SO₂ Molecular formula = SO₂
What would be the effect of each of these things on equilibrium a) position and b) constant, Keq?: 1. Adding reactants 2. Adding products
1. (Adding reactants) a) Shift position toward products b) No effect on Keq 2. (Adding products) a) Shift position toward reactants b) No effect on Keq
What would be the effect of each of these things on equilibrium a) position and b) constant, Keq?: 1. Increasing Pressure 2.Decreasing Pressure
1. (Increasing Pressure) a) Would shift the equilibrium position toward whatever side of the reaction has less moles of gas, in order to decrease the pressure b) No effect on Keq 2. (Decreasing Pressure) a) Would shift the equilibrium position toward whatever side of the reaction has more moles of gas, in order to increase the pressure b) No effect on Keq
What would be the effect of each of these things on equilibrium a) position and b) constant, Keq?: 1. Taking away reactants 2. Taking away products
1. (Taking away reactants) a) Shift position toward reactants b) No effect on Keq 2. (Taking away products) a) Shift position toward products b) No effect on Keq
What would be the effect of each of these things on equilibrium a) position and b) constant, Keq?: 1. Increasing activation energy 2. Adding a catalyst 3. Stabilizing the transition state
1. (↑ Ea) a) No effect on equilibrium position. Would just slow down reaction rate. b) No effect on Keq. Would just slow down the rate at which Keq is reached 2. (+ catalyst) a) Catalysts decrease activation energy. This would not effect equilibrium position or b) Keq. It would just speed up the rate at which equilibrium is reached 3. (Stabilizing transition state) a) More stable transition state = lower energy transition state = lower activation energy. Would not effect position or b) Keq. Would act just like adding a catalyst/lowering the Ea.
1. Find units of k for a first order reaction. 2. What are the variables on the graph for a first order reaction? 3. What is the slope on the graph for a first order reaction?
1. First order: Rate = k[A]¹ k = Rate/[A] k = M/s/M Molarity cancels k = 1/s 2. ln[A] vs. time 3. -k
What conditions absolutely must be met in order for a chemical reaction to take place?
1. Reactants must collide with enough kinetic energy to overcome the activation energy barrier 2. Reactants must be in the correct spatial orientation relative to each other in order to react with each other
1. Find units of k for a second order reaction. 2. What are the variables on the graph for a second order reaction? 3. What is the slope on the graph for a second order reaction?
1. Second order: Rate = k[A]² k = Rate/([A]²) k = M/s/M² k = 1/s/M k = 1/s*1/M k = M⁻¹S⁻¹ or 1/(M*s) 2. 1/[A] vs. time 3. +k
1. Find units of k for a zero order reaction. 2. What are the variables on the graph for a zero order reaction? 3. What is the slope of the graph for a zero order reaction?
1. Zero order: Rate = k[A]⁰ k = Rate/([A]⁰) k = M/s/1 k = M/s 2. [A] vs. time 3. -k
We currently have 500g of element Z. The half-life of element Z is 10 years. How much of element Z will remain 40 years from now?
31.25 g m = 500 g t1/2 = 10 years t = 40 years Original amount: 500 g Half life one: 250 g Half life two: 125 g Half life three: 62.5 g Half life four: 31.25 g Answer: After 40 years, 31.25 g of element Z will remain.
Explain what a coordinate covalent bond is
A coordinate covalent bond is a bond where ONE atom donates BOTH of the electrons. The atom that donates electrons must have a lone pair. The atom that accepts electrons must have a positive charge, a partial positive charge, or empty d-orbitals. An important example of a coordinate covalent bond is the heme iron that coordinates to nitrogen atoms in hemoglobin.
Conceptual definition of half life. What quantity changes each half life?
A half life, or t1/2, is the TIME it takes for the substance's MASS to be cut in HALF. For example, if we start out with 10g of a substance, after one half life, we'd have 5g, and after two half lives, we'd have 2.5g, etc.
What is one way to think of a neutron conceptually?
A neutron = a proton⁺ + an electron⁻ = °
What is one way to think of a proton conceptually?
A proton = a neutron° + a positron⁺ = ⁺
Describe the current, accepted version of what an atom looks like (Think of how this is different from the Bohr model of the atom, which was the first (mostly inaccurate) model of the atom.)
An atom has protons and neutrons at its core. Protons and neutrons are held together by the strong nuclear force. Protons and neutrons have the same mass and size, and are 2000x more massive than electrons. Most of the atom's mass is concentrated in the nucleus, then. Electrons are very tiny, about 1/2000th of the mass of a proton. Because electrons are so tiny compared to the size of the electron cloud or the nucleus, atoms are mostly empty space. Heisenberg Uncertainty Principle: The exact location (position) and velocity/momentum of an electron cannot be known at the same time We only know where electrons will most likely be based on probabilities Electrons exist in s, p, d, and f orbitals (probability functions) around the nucleus
In Trial 1, students bombard a sample of Fe with photons of frequency f and electrons are ejected. If in Trial 2, they increase the frequency of the photons used, which of the following will result? a) The # of electrons ejected will increase b) The speed of the electrons leaving the iron will increase c) The current created by the emitted electrons will increase d) The number of electrons ejected will decrease, but the energy of each electron will increase.
Answer = b) The speed of the electrons leaving the iron will increase a) The # of electrons ejected will increase b) The speed of the electrons leaving the iron will increase c) The current created by the emitted electrons will increase d) The number of electrons ejected will decrease, but the energy of each electron will increase. E = h*f E = work function + KE KE = 1/2mv² hf = work function + 1/2mv² If you increase the frequency, you increase the energy, and all extra energy above and beyond the work function (energy req. to eject an electron) goes into the kinetic energy of the electron that is ejected. Therefore, the same number of electrons would be ejected, but each of them would be ejected with a greater velocity.
If the initial amount of a substance is 400g, and the final amount of a substance after 28 days is 25g, what is the half life of the substance?
Answer: 7 days Count how many half lives have taken place between the initial and final mass: Zero: 400 g One: 200 g Two: 100 g Three: 50 g Four: 25 g Four half lives have taken place over 28 days. 28 days/4 half lives = 7 days/ 1 half life So, t1/2 for this substance = 7 days.
The most naturally abundant iron isotope, ⁵⁶Fe, decays to form ⁵⁶Mn. During the decay process, which of the following could have occurred? I. An electron was captured II. A positron was emitted III. A gamma ray was emitted
Answer: All of them - I. An electron was captured II. A positron was emitted III. A gamma ray was emitted. ⁵⁶Fe → ⁵⁶Mn Mn atomic number is 25 and Fe atomic number is 26, so: ⁵⁶₂₆Fe → ⁵⁶₂₅Mn Make atomic numbers match on each side: ⁵⁶₂₆Fe → ⁵⁶₂₅Mn + e⁺¹(positron) OR ⁵⁶₂₆Fe + ₋₁e → ⁵⁶₂₅Mn - gamma ray emission is just a byproduct of all the other types of radioactive decay. It doesn't change the identity of the new element, so it could have happened along with positron emission or electron capture.
A chemist could identify the order of zinc in the rate law for the equation given below by performing which of the following procedures in the lab? (Note: sulfuric acid is known to be a first order reactant) Zn(s) + H₂SO₄(aq) → ZnSO₄(s) + H₂(g) a) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while holding the H₂SO₄ constant. b) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while varying the [H₂SO₄]. c) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while holding the [H₂SO₄] in excess. d) The order of Zn is already known because solid reactants are always zero order and therefore omitted from the rate law.
Answer: c) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while holding the [H₂SO₄] in excess. a) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while holding the H₂SO₄ constant. b) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while varying the [H₂SO₄]. c) Graph the [Zn], ln[Zn] and 1/[Zn] vs. time while holding the [H₂SO₄] in excess. d) The order of Zn is already known because solid reactants are always zero order and therefore omitted from the rate law. → *Solid (and liquid) reactants are always omitted from the Keq expression, but NOT from the rate law.* - We already know the order of sulfuric acid, H₂SO₄, so now we need to put sulfuric acid in excess so that it doesn't affect our measurement of how Zn affects the reaction rate. - We will need to make three graphs for Zn vs time, using the variables for a zero order, first order, and second order reactant, and then see which one is linear to determine the order of Zn
How many more neutrons are there than electrons in ⁵⁴Fe⁺? a) 0 b) 1 c) 2 d) 3
Answer: d) 3 ⁵⁴Fe⁺ Mass Number (A) = 54 → protons + neutrons Atomic Number (Z) for iron (see periodic table) = 26 → protons 54 - 26 = 28 → neutrons How many electrons?: Should be 26 to match protons, but since there's a +1 charge, there are 25 electrons. 28 neutrons - 25 electrons = 3 more neutrons than electrons.
For a reaction where A + B → C, and B is known to be in excess, a non-linear plot of ln[A] vs. time indicates that the reaction is: a) first order wrt reactant A b) possibly first order wrt reactant A c) possibly first order wrt reactant A, but is not first order after all d) not first order wrt reactant A
Answer: d) not first order wrt reactant A a) first order wrt reactant A b) possibly first order wrt reactant A c) possibly first order wrt reactant A, but is not first order after all d) not first order wrt reactant A - plot of ln[A] vs. time is the plot for a first-order graph. Because it's NON-linear, and B is in excess so B doesn't affect the rate, we know that reactant A must NOT be first order.
How will increasing the temperature affect the reaction rate?
Because Temperature is a measure of the average kinetic energy of all the molecules in a substance, if you increase the temperature, you increase the kinetic energy of the reactants so that they are more likely to have enough KE to overcome the Ea barrier. This would increase the reaction rate.
Why do all of the periodic trends, besides metallic character, increase in the opposite direction of atomic radius?
Because metals are large, as metallic character increases (down and to the left), atomic radius also increases. We know that metals are large and that their electrons are very LOOSELY held. SMALL molecules (nonmetals) hold onto their electrons very TIGHTLY. So electronegativity increases along with NONmetallic character, up and to the right. Electron affinity is also greater for nonmetals, which hoard electrons, like to gain electrons, and hold tightly to them, so electron affinity also increases with nonmetallic character, up and to the right. Because NONMETALS are small and hold tightly to their electrons, we know that atomic radius must increase in the opposite direction of nonmetallic character, as you get further away from the nonmetals and closest to the larger metals. Ionization energy, which is the amount of energy REQUIRED (NOT RELEASED) to remove a valence electron, increases up and to the right, along with nonmetallic character, because with nonmetals, their electrons are held so tightly that it requires a LOT of energy to remove a valence electron.
What is bond energy/bond dissociation energy? What is the connection between stability and bond energy?
Bond energy, or bond dissociation energy, is the amount of energy REQUIRED to break a bond. Always remember that BREAKING a bond REQUIRES energy, and FORMING a bond RELEASES energy. (Bonds like to form. They don't like to be broken). Stable bonds = HIGH bond energy → A lot of energy is required to break a stable bond Unstable bonds = LOW bond energy → Not very much energy is required to break a bond that is already unstable.
Describe Sigma Bonds and the important things to know about them
Bonding occurs when orbitals that are parallel to each other on adjacent atoms overlap. • Sigma (σ) bond: Direct bond in the plane of the nuclei ○ They form between orbitals that are pointed directly, head on at each other ○ Bond is in between the two atom's nuclei ○ Can form between two atoms of any size
Why do bonds form? Is energy required or released when they form? Explain this in terms of ATP hydrolysis, and why that tends to confuse people.
Bonds form when there are more electrons in (low energy) bonding orbitals than in anti-bonding orbitals, so the two atoms bonded together would have LOWER energy, and be more stable than each atom would have on its own. Energy is released when bonds form, because bond formation is a favorable process. (Energy is required when bonds break, because breaking bonds is an unfavorable process.) When we think of ATP hydrolysis, we often think of breaking a bond to release energy. But actually, breaking a bond requires energy, and forming a bond releases energy. But what is actually going on in ATP hydrolysis is the bonds that are FORMED to recreate ADP (+ Pi) RELEASE more energy than is required to break the bonds in ATP. That energy that is released in forming ADP + Pi can be used to break other bonds. So forming bonds always releases energy, and breaking bonds always requires energy.
Which of the following steps will increase the percent yield during the base-catalyzed decarboxylation of CH₃COCH₂COOH? a) Increasing the amount of base b) Increasing the temperature c) Removing CO₂ d) Increasing the initial concentration of CH₃COCH₂COOH
CH₃COCH₂COOH + :B ⇌ CH₃COCH₃ + B-H + CO₂ a) Increasing the amount of base → will push reaction toward products, but will not change % yield b) Increasing the temperature → Will speed up rate of reaction, but will not change % yield c) Removing CO₂: CORRECT ANSWER → Will increase % yield, because when you artificially remove products, through Le Chatelier's principle, the reaction will keep producing more products to maintain equilibrium d) Increasing the initial concentration of CH₃COCH₂COOH → Will push reaction toward products,
In a sealed container at room temperature, a student is observing the endothermic decomposition reaction wherein sulfuric acid is broken down into water, sulfur dioxide, and diatomic oxygen. After the rxn has reached equilibrium, the student transfers the entire contents of the reaction vessel into an evacuated vessel with twice the volume. Which of the following is expected AFTER the transfer? a) Less water will be produced b) Amount of sulfur dioxide gas present will increase c) Less sulfuric acid will decompose d) The reaction rate will increase due to the reduced pressure
CORRECT: b Unbalanced reaction: H₂SO₄(l) ⇌ H₂O(l) + SO₂(g) + O₂(g) - What change is occurring?: Volume is being increased by a MF of 2 → How does Volume∆ affect Pressure∆? PV = nRT V = 1/P →Find MF for Pressure: 2 = 1/P 2*P = 1 P = 1/2 MF for Pressure = 1/2 Pressure decreases by 1/2 → Decreasing pressure → reaction will move toward side with more moles of gas - Write and balance the reaction: 2H₂SO₄(l) ⇌ 2H₂O(l) + 2SO₂(g) + O₂(g) - reaction will shift toward the products a) Less water will be produced → FALSE: More water will be produced b) Amount of sulfur dioxide gas present will increase → TRUE: Correct answer c) Less sulfuric acid will decompose → FALSE: More sulfuric acid will decomopose d) The reaction rate will increase due to the reduced pressure → FALSE: Changing the pressure will affect the equilibrium position, but NOT the reaction rate. Adding a catalyst would increase the reaction rate.
What effect would adding CO₂ have on the pH of a person's blood? CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ Adding CO₂ would shift the carbonic reaction RIGHT, resulting in an increase in acid concentration, or a DECREASE in blood pH.
In what scenario would you expect to see an increase in bicarb levels in a person's blood? CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ Any scenario that would result in a shift to the right would cause the concentration of bicarb to rise, so for example: - taking away H⁺ through an increase in pH → alkalosis would cause increased bicarb - adding CO₂ to the blood stream by impaired gas exchange or not breathing frequently enough would cause a right shift and an increased bicarb concentration
What effect does an increase in acid concentration have on blood pH during ketoacidosis?: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ _______ pH, shifting equation to the _______.
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ DECREASES pH, shifting the equation to the LEFT as system works to restore equilibrium. In effect, ↑[acid] in blood (acidosis)→ ↑[CO₂] in blood, through Le Chatelier's Principle.
What is the electron configuration of calcium in calcium sulfate?
Ca normally has 20 electrons sulfate has a 2- charge, so Ca must have a 2+ charge Ca²⁺ has 20 - 2 = 18 e- Go to calcium, and move back to spaces on periodic table: You get Argon. Argon is in 3p block, has 18 e- Use orbital filling diagram to get electron configuration: Answer = 1s² 2s² 2p⁶ 3s² 3p⁶
How would increasing the concentration of a catalyst affect the rate of a reaction?
Catalysts lower activation energy, so that reactant molecules are more likely to collide with enough KE to produce a reaction. Increasing the amount of catalyst will increase the reaction rate at first, but once you have much more catalyst in relation to reactants, you decrease the likelihood that the reactants will even encounter each other and react in the first place.
Explain the size differences between cations, anions, and neutral versions of the same element.
Cations are smaller than neutral elements because: They have less electrons, so their electron clouds are not as wide. They are more positively charged, so they are "sucked in" by the positively-charged protons in the nucleus Cations lose e-s to gain the electron configuration of the nearest noble gas, meaning they lose an entire electron shell, which reduces their volume substantially. *MNEMONIC= SMALL CAT Anions are larger than neutral elements because: They have extra electrons, so their electron clouds are more spread out
What would be the effect of each of these things on equilibrium a) position and b) constant, Keq?: 1. Increasing Temperature 2. Decreasing Temperature
Changing the temperature is the only thing that will change the Keq. This is because Keq is defined differently for each specific temperature. 1. (Increasing Temperature) For an exothermic reaction: a) Would shift the reaction toward the reactants, because increasing the temperature is like adding a product (heat) b) Keq would decrease, because of the shift toward reactants For an endothermic reaction: a) Would shift reaction toward the products, because increasing the temperature would be like adding a reactant b) Keq would increase, because of the shift toward products 2. (Decreasing Temperature) For an exothermic reaction: a) Would shift reaction toward products, because decreasing temperature would be like taking away a product (heat) b) Would increase Keq, because of the shift toward products For an endothermic reaction: a) Decreasing the temperature would shift the reaction toward the reactants side, because taking away heat from an endothermic reaction would be like taking away a reactant. b) Would decrease Keq, because of the shift toward reactants
Hypochlorite ion
ClO⁻
Chlorite ion
ClO₂⁻
Chlorate ion
ClO₃⁻
Perchlorate ion
ClO₄⁻
Write a balanced chemical reaction for the combustion of propanol.
Combustion = Organic compound + O₂ → CO₂ + H₂O Propanol= C₃H₈O 1. Write out basic equation: C₃H₈O + O₂ → CO₂ + H₂O 2. *Balance elements in the order "CHO"*: 3. Balance Carbon: C₃H₈O + O₂ → 3CO₂ + H₂O 4. Balance Hydrogen: C₃H₈O + O₂ → 3CO₂ + 4H₂O 5. Balance Oxygen: C₃H₈O + 4¹/₂ O₂ → 3CO₂ + 4H₂O 6. Balance Remaining Elements: There are none 7. Multiply BOTH SIDES by the reciprocal of the denominator of any fraction (to get rid of the fractions in the coefficients): 2*(C₃H₈O + 4¹/₂ O₂) → (3CO₂ + 4H₂O)*2 = 2C₃H₈O + 9O₂ → 6CO₂ + 8H₂O 8. Make sure it's balanced correctly: 6 C, 16 H, 20 O → 6 C, 16 H, 20 O 9. Balance charges on both sides: No charges in this equation Balanced equation = 2C₃H₈O + 9O₂ → 6CO₂ + 8H₂O
1) What would the condosity of a 2.0 M KCl solution be? 2) What would be the expected condosity of a 3.0 M solution of LiCl?
Condosity = The molar concentration of a NaCl (saline) solution that would conduct electricity equally as well as the solution in question. *CONDuctivity CONDosity* 1) Look at periodic table → metallic character → K more metallic than Na → K conducts electricity better than an equimolar soln of Na → Would need more Na to achieve same conductance → Condosity =GREATER than 2.0 M NaCl. 2) Look at periodic table → Li is less metallic than Na → Li will not conduct as well as Na → need a smaller amount of Na → Condosity = LESS than 3.0 M NaCl.
What is Coulomb's Law? What does it represent, and what other formula is it analogous to?
Coulomb's Law is the equation for the Force on a charge. In chemistry, we use it to refer to the attractive force that the positive nucleus has on the negative valence e-s. Coulomb's Law: F = k*q₁*q₂/r² Exactly analogous to the formula for gravitational force, which is also an attractive force between two species: Fgravitational = G*m₁*m₂/r²
What main process do we think of when we think of electron capture? What else happens during electron capture, and how would we figure this out?
During electron capture, an electron is captured or absorbed by an unstable atom. Start writing the electron capture equation, using arbitrary/random element numbers and symbols: ¹⁰⁰₆₇E + ₋₁e → ? Now balance out the equation, so that the total atomic number, Z, is equal on both sides: ¹⁰⁰₆₇E + ₋₁e → ¹⁰⁰₆₆F Evaluate what has happened to Z: Z decreases by one. This means that one proton has become a neutron. Therefore, in electron capture: (1) An electron is captured/absorbed (2) one proton becomes a neutron
How is energy released/absorbed related to the frequency of a photon released/absorbed?
E= h*f E= energy, Joules h = Planck's constant (given) f = frequency High frequency = high energy
describe the mnemonic for quantum numbers about where an electron "lives."
Each electron has a specific home address inside an atom. Each electron would like to share a room with its twin, if possible. First Quantum Number: Electron's street number - n - Principle quantum number - highest energy level - shell Second Quantum Number: Electron's House - azimuthal, or angular momentum quantum number - l - gives SHAPE of orbital → think, each HOUSE has a different SHAPE Third Quantum Number: Electron's Room - magnetic quantum number -ml - gives ORIENTATION of orbital - WHERE IS THE ROOM IN THE HOUSE? Fourth Quantum Number: Twin (can be +1/2 or -1/2) - spin quantum number - *MNEMONIC = TWIN SPIN* - ms
What is a conceptual way to remember the equation for energy of a photon released/absorbed?
Energy is directly proportional to FREQUENCY. High frequency = high energy E = h*f Energy = Planck's constant (given)*frequency
What is dynamic equilibrium, and what factors are able to change a reaction's equilibrium constant?
Equilibrium only exists for REVERSIBLE reactions in a closed system. Is the point at which the rate of the forward reaction = the rate of the reverse reaction, so there is no NET forward or backward reaction happening. Equilibrium constant, Keq is defined for a specific TEMPERATURE. A change in temperature is the only factor that can change the Keq. All other factors can only change the POSITION with respect to equilibrium. **Important: Keq ONLY includes AQUEOUS SOLUTIONS and GASES. It DOES NOT include pure liquids or solids. Keq = [products]^x/[reactants]^y, where x and y = the coefficients in the balanced reaction. A reaction's Keq basically describes, then, to what extent a reversible reaction naturally favors products or reactants.
-What really IS a reaction order? -How do you find it?
If X = change in reactant CONCENTRATION between two experimental trials, and Z = change in reaction RATE during those same two experimental trials, and X^Y = Z, Y = reaction order for that specific reactant.
How would increasing the energy of the reactants affect the reaction rate?
If you increase the energy of the reactants, this would make them more likely to have enough energy to surpass the Ea barrier, and would increase the rate at which they react.
What happens during the process of alpha decay? What is an alpha particle?
In alpha decay, an unstable atom loses an alpha particle, or a helium nucleus. For example, ²⁵⁶₁₀₃Lr → ²⁵²₁₀₁Md + ⁴₂He
What is the main particle that's gained or lost in beta decay? What else happens in beta decay, and how would we figure this out through thinking through the particle that is lost?
In beta decay, an atom loses an electron. Start writing a beta decay equation with a random element symbol, E, with two arbitrary numbers: a mass number, A, and an atomic number, Z. Show that it loses an electron: ²³²₁₄₄E → ₋₁e Balance the equation to make the total Z (atomic number) match on both sides, while A stays the same: ²³²₁₄₄E → ₋₁e + ²³²₁₄₅F We see that the atomic number on the right side has increased by one from the left side, and the mass number has stayed the same. We know now, that this must mean that one neutron has changed into a proton. Therefore, we know that in beta decay: (1) we lose and electron, and (2) a neutron becomes a proton. *Easier way to figure out what happened: Beta decay is losing an electron. A neutron = a proton + an electron, so if you lose an electron, a neutron becomes a proton.
Describe molecular orbital theory. What is bonding versus anti-bonding, and how do we use the relative amount of each to determine the stability of a bond and whether or not that bond will form?
In molecular orbital theory, we think of electrons as being delocalized over a molecule rather than concentrated in covalent bonds. Each possible covalent bond includes forces that support bonding, and forces that do not support bonding of the two atoms. Electrons have "phases", because of their wave-like properties. Electrons attract each other when they are in phase, and repel each other when they are out of phase. A bonding orbital is a region of high electron density between the nuclei of two atoms. This is where a bond forms. Bonding orbitals contain electrons that are "in phase" with each other, and are attractive to each other Bonding orbitals have LOWER ENERGY compared to antibonding orbitals. Antibonding orbitals are regions of ZERO electron density between the nuclei of two atoms, where bonds CANNOT form. Anti-bonding orbitals contain electrons that are "out of phase" with e/o, and are repulsive to e/o. Anti-bonding orbitals have HIGHER ENERGY than bonding orbitals, and are unstable. Whether a bond will form or not depends on the bond's stability. More stable = lower energy. Theoretically, the stability of a covalent bond depends on whether bonding orbitals (lower energy) outweigh anti-bonding orbitals (higher energy), or vice-versa. If bonding > antibonding, the covalent bond will have lower energy, and be more stable than the two atoms would be separately. A covalent bond would form. If antibonding > bonding, the covalent bond would have higher energy, and be more unstable compared to the two atoms on their own. No covalent bond would form in this situation.
Which two elements in the periodic table, if united in a bond, would create a bond with the maximum possible ionic character?
Ionic character = Degree of electronegativity difference between two atoms. Ionic character exists for ionic bonds, obviously, but covalent bonds can have ionic character (electronegativity difference), as well. Answer: Francium (element with greatest metallic character) bonded to Fluorine (element with greatest nonmetallic character). Metals hold loosely to e⁻s and have low electronegativity, while nonmetals hold tightly to e⁻s and have high electronegativity.
How do you express Keq in terms of pressures for a reaction involving gases, such as A(g) + B(g) ⇌ C(g) + D(g)?
Keq using pressure = Kp For A(g) + B(g) ⇌ C(g) + D(g): Kp = PC^x * PD^y/PA^x * PB^y PA = Partial pressure of gas A Ptotal = PA + PB + PC... = all the partial pressures added up PA = XA * Ptotal = mole fraction * total pressure XA = mole fraction of A = (moles of gas A)/(total moles of gas present)
What is the difference between kinetics and thermodynamics? How does a reaction's kinetics affect its thermodynamics, and vice-versa?
Kinetics: SPEED of a reaction. Depends on things like temperature (aka the average kinetic energy of the molecules), catalysts, activation energy, reaction order, reaction rate, rate constant, etc. Thermodynamics: ENERGETICS of a reaction. Thermodynamics determine the SPONTANEITY of a reaction. Associated with things like bond dissociation energy, ΔH, ΔS, ΔG, Keq, etc. KINETICS AND THERMODYNAMICS ARE COMPLETELY INDEPENDENT, and do not affect each other at all.
What does Le Chatelier's principle say, and how does it predict what will happen to the equilibrium position of a reaction?
Le Chatelier's Principle describes how when a change is made to a reversible reaction that is in equilibrium, the equilibrium POSITION will shift in order to cancel out the change in equilibrium position that was created by the change. The changes made must be canceled out, so that Keq/Kp always stays constant and doesn't change.
how do you determine n for an atom's valence electrons?
Look at which period it is in in the periodic table.
How can you figure out the direction of the periodic trend for atomic radius from the definition of a metal (and metallic character)?
Metals (right side of the periodic table) are defined as large atoms whose electrons are held very LOOSELY, i.e. "a sea of electrons". Because we know that metals are large, and metallic character INCREASES DOWN and to the LEFT on the periodic table, we know that atomic radius ALSO INCREASES DOWN and to the LEFT on the periodic table.
Manganate ion
MnO₄²⁻
Permanganate ion
MnO₄⁻ Think of: Potassium permanganate's formula is KMnO₄, and it is a neutral compound. We know potassium has a ⁺¹ charge, so permanganate must have a ⁻¹ charge.
A metal is known to have a work function of 500 J. If a photon of 500 J strikes the surface of the metal, what will happen?
Nothing will happen. φ = Work function = energy required to eject one e- from a solid metal φ = 500 J Eadded = φ + KEelectron There is no extra energy to contribute to the ejected electron's kinetic energy, so the electron will not actually be ejected from the metal.
Pauli Exclusion Principle
Pauli Exclusion Principle says: No two electrons in the same atom or molecule can have the same four quantum numbers (Twins can have three of the same quantum numbers, but their ms (twin) numbers would be different.) Only two electrons can occupy each orbital. (For # of orbitals per orbital shape/subshell, see picture): If there are open orbitals available, electrons will each take their own orbital. But if there aren't enough rooms, they are forced to share an orbital/room with their twin.
Describe Pi Bonds and the important things to know about them
Pi bonds: Bond above and below the plane of the nuclei ○ Form from side-to-side overlap of orbitals that are parallel to each other ○ Bond forms above and below the nuclei of both atoms ○ With two large atoms, parallel orbitals can be far apart and won't overlap well enough to form a pi bond. ○ So, larger atoms don't form pi bonds with each other. ○ Pi bonds do NOT allow for free rotation. Pi bonds lock the two molecules that are pi-bonded together in place. Double Bond = One sigma bond and one pi bond Triple Bond= One sigma bond and two pi bonds, which are oriented perpendicularly to each other.
What is the main particle we need to think of relating to positron emission? Is this particle gained or lost? What else happens during positron emission, and how would we figure this out?
Positron emission = loss of a POSITRON (positive electron), or an electron with a positive charge, e+. The + sign should be down and to the left of e, because that is its Z number. Start out with a random element, called E. Assign it arbitrary mass and atomic numbers. Write out the equation where it loses a positron. ⁵⁵₄₃E → e+ Balance the equation to make the total Z match on both sides: ⁵⁵₄₃E → e+ + ⁵⁵₄₂F Evaluate what has happened: Z has decreased by one, so a proton must have become a neutron Therefore, in Positron Emission: (1) A positron is emitted (2) a proton becomes a neutron *Easier way to think about this: Positron emission = loss of a positron, or a positive electron (e+). A proton = a neutron + a positron, so if you lose a positron, a proton has effectively become a neutron.
- How will increasing the concentration of products affect the reaction rate? - How will decreasing the concentration of products affect the reaction rate?
Products don't have any effect on reaction kinetics. This is because rate laws are only written with reactants in mind, and the rate is defined as the change in concentration of the reactants over time, not the products. So basically, kinetics/reaction rate only depends on the reactants.
Difference between Q and Keq. What happens if Q > K? What happens if Q < K?
Q, the reaction quotient, is like Keq, but is calculated when the reaction is NOT at equilibrium. You can compare Q with Keq to see how far away from equilibrium the reaction is. If Q > K, there are more products than the equilibrium favors, so the reaction will SHIFT TOWARD REACTANTS. If Q < K, there are more reactants than the equilibrium favors, so the reaction will SHIFT TOWARD PRODUCTS.
What are the units for reaction rate?
Reaction rate is measured in Molarity of reactants/second, or M/s, or how fast reactants are consumed over time.
What is a conceptual way of remembering the formula for speed of light in a vacuum?
SPEED = velocity without direction = m/s To get correct units, m/s: NEED m*(1/s) = m*Hz = wavelength*frequency c = λ*f λ = wavelength, m f = frequency, Hz or s⁻¹ Remember, speed of light, c = 3.0x10⁸ m/s
Which element, in its ground state, has the same electron configuration as sodium ion?
Sodium ion = Na⁺ missing one electron → go backward one element element = Ne (neon), a noble gas
What is the physics definition of temperature? How does temperature relate to activation energy?
Temperature = The average Kinetic Energy of the molecules in a substance. As temperature increases, the average kinetic energy of the molecules in the substance increases. Molecules are more likely to have enough KE to overcome the activation energy barrier at higher temperatures.
Describe the Aufbau Principle, and draw the orbital filling diagram.
The Aufbau Principle says that in an atom's ground state, electrons will fill the lowest-energy orbitals first, before they fill the higher-level orbitals. In this way, each atom, in its ground state, attains the lowest-energy (most stable) electron configuration possible.
What is the work function? What does it describe and what is the equation that includes it (think conceptually)?
The amount of energy input required to eject an electron FROM A SOLID METAL = the work function, φ. All excess energy added goes into the Kinetic Energy of the ejected electron. Eadded = φ + KE KE = Eadded - φ
What is the difference between mass number and atomic number?
The mass number, A = # protons + # neutrons in an atom's nucleus. The atomic number, Z = # protons. The number of neutrons, N is therefore A-Z Elements are written like (see picture): where X is the chemical symbol for the element.
Explain how to name the polyatomic ions that chlorine forms using prefixes and suffixes
The names depend on the number of oxygens. Greatest # of oxygens = per-ate Smallest # of oxygens = hypo-ite ClO₄⁻ = perchlorate ion ClO₃⁻ = chlorate ion ClO₂⁻ = chlorite ion ClO⁻ = hypochlorite ion
Name the important characteristics of metals
Think of as "Positive charge in a SEA OF ELECTRONS" → Large atoms with LOOSELY-HELD ELECTRONS Give up electrons easily Electropositive Low Bond Dissociation Energy Form cations OIL RIG: Tend to get oxidized Metals don't normally melt → high melting point lustrous: shiny malleable: pliable → can be hammered into thin sheets without breaking ductile: stretchable, can be rolled into thin wires excellent conductor → conducts heat and electricity
Name the important characteristics of nonmetals
Think of as the OPPOSITE OF METALS: Small atoms that hold on tightly to their electrons hold tightly to electrons → electronegative like to gain electrons→ tend to form anions OIL RIG: tend to get reduced form ionic bonds with metals, and covalent bonds with other nonmetals (think of the covalent molecules in organic chem.)
When an electron falls from a high energy level (n) to a low energy level, it ______ a photon.
When an electron falls from a high energy level to a low energy level, it emits a photon. Oppositely, when an electron jumps from a lower energy level to a higher energy level, it absorbs a photon. It does this according to the equation: E(absorbed or released) = -2.2178 x 10-18 J*(1/nfinal² - 1/ninitial²)
Which electron configurations are elements trying to attain when they form ions?
When elements form ions, they are trying to form the same electron configuration as a NOBLE GAS. For example, chlorine forms chloride ion, Cl⁻. If you move one element forward for the extra electron, you get Ar, a noble gas. Magnesium forms magnesium ion, Mg²⁺. If you move backward two elements on the periodic table, for two missing electrons, you get Ne, a noble gas.
What do we need to remember to always do when we see a half life problem?
Write it out!!
For this set of data, determine the rate law for the reaction, and the overall order of the reaction: 2NO(g) + 2H₂(g) → N₂(g) + H₂O(g) (@ 1280C). Expt. 1: [NO] = 0.0050 M, [H₂] = 0.0020 M, Initial rate = 1.25 x 10⁻⁵ M/s Expt. 2: [NO] = 0.0100 M, [H₂] = 0.0020 M, Initial rate = 5.00 x 10⁻⁵ M/s Expt. 3: [NO] = 0.0100 M, [H₂] = 0.0040 M, Initial rate = 1.00 x 10⁻⁴ M/s
X = ∆ in [reactant], Z = ∆ rate X^Y = Z Solve for Y to get reactant's order: For NO: Between expt. 1 and expt. 2: X = 2 Z = 4 2^y = 4 y = 2 NO is 2nd order For H₂: Between expt. 2 and expt. 3: X = 2 Z = (1.00 x 10⁻⁴ → laRS → 10.0 x 10⁻⁵) 10.0 x 10⁻⁵/5.00 x 10⁻⁵ = 2 Z = 2 X^Y = Z 2^Y = 2 Y = 1 H₂ is 1st order Rate law = k[NO]²[H₂]¹ Overall order = 2 + 1 = 3rd order
Will the MCAT ever give you unbalanced equations and not tell you that they're unbalanced?
YES!! Make sure every equation is balanced on the MCAT!
What is Zeffective? Describe the nature of the relationship between Zeffective and atomic radius, using the concept of shielding.
Zeffective = effective nuclear charge = magnitude of positive charge from the nucleus that is felt by the furthest valence e-s in an atom. Zeffective DECREASES as atomic radius INCREASES, or valence electrons feel a weaker positive charge from their nucleus in bigger atoms. This is because of SHIELDING, or the fact that larger atoms have more electrons + more electron shells, and the electron shells in between the nucleus and the valence electrons "shield" the valence electrons from the attractive force (positive charge) of the nucleus.
Describe correlation between atom size and Zeffective (effective nuclear charge).
Zeffective, or effective nuclear charge, is the magnitude of positive charge from the nucleus that is felt by the furthest-out, valence electrons. LARGER atoms with MORE electrons + more shells feel a SMALLER magnitude of positive charge from their nucleus, because the atoms in-between the valence e-s and the nucleus SHIELD the valence e-s from the nucleus' positive charge.
A student accidentally used an unclean apparatus to begin an expt. Exactly 3.0 mL of HCl gas remained in the enclosed reaction vessel at the start of the experiment. If the student must report the total moles of HCl formed by a reaction run inside the apparatus, by how many moles will his data be in error? (Assume T = 25°C; Density of HCl = 1.21g/cm³) a) 0.98 b) 0.098 c) 0.3 d) 0.03
a) 0.98 b) 0.098 c) 0.3 d) 0.03 1 mL = 1cc = 1 cm³ 3.0 mL HCl = 3.0 cm³ HCl 3.0 cm³ HCl*(1.21 g HCl/1 cm³) = 3.63 g HCl molar mass of HCl = 1 + 35.45 = 36.45 g/mol 3.63 g HCl*(1 mol HCl/36.45 g HCl) = 3.63 x 10⁰*(1/3.645 x 10¹) = 1.0 x 10⁻¹ mol HCl = 0.100 mol HCl Answer = b) 0.098 mol HCl
How many hydrogen atoms are present in 2.0g of water? a) 1.33 x 10²³ b) 6.67 x 10⁻¹ c) 6.67 x 10²² d) 2.22 x 10⁻¹
a) 1.33 x 10²³ b) 6.67 x 10⁻¹ c) 6.67 x 10²² d) 2.22 x 10⁻¹ 2.0 g H₂O*(1 mol water/18.02 g water) = 1/9 mole water = 0.11 mole water = 1.1 x 10⁻¹ mole water 1.1 x 10⁻¹ mole water*(2 moles hydrogen/1 mole water = 2.2 x 10⁻¹ moles hydrogen 2.2 x 10⁻¹ moles hydrogen*(6.022 x 10²³ hydrogen atoms/1 mole hydrogen) = 13.2 x 10²² hydrogen atoms = 1.32 x 10²³ hydrogen atoms Answer = a) 1.33 x 10²³
a) How do you figure out the electron configuration of a cation? b) How do you figure out the electron configuration of an anion?
a) First go to the element on the periodic table. A cation is missing one electron, so move BACKWARD by one element (for one less e-), and give the configuration of that element. b) Go to the element on the periodic table. An anion has one extra electron, so move FORWARD by one element (for one extra e-), and give the configuration of that element.
Explain how to name these acids: a) H₂SO₃ b) H₂SO₄ c) H₂S
a) H₂SO₃ = sulfurous acid SO₃²⁻ = sulfite ite → ous = sulfurous acid b) H₂SO₄ = sulfuric acid SO₄²⁻ = sulfate ate → ic = sulfuric acid c) H₂S = hydrosulfuric acid S²⁻ = sulfide ion ide → hydro + ic acid = hydrosulfuric acid
What are the three naming rules (suffix changes) you need to remember when naming inorganic acids?
ate → ic ite → ous "sounds like hideous" ide → hydro + ic acid "like HCl = hydrochloric acid"
How is the speed of light (c) related to the frequency and wavelength of a photon, and to the energy absorbed or released?
c = λ*f Speed (m/s) = wavelength (m) * frequency (s^-1 or Hz) c = speed of light in a vacuum = 3.0 x 10⁸ m/s λ (lambda) = wavelength f = frequency E = h*f f = c/λ E= h*(c/λ)
how do you determine l for an atom?
l= orbital shape l = 0→(n-1) l = 0 = s orbital l = 1 = p orbital l = 2 = d orbital l = 3 = f orbital
how do you determine ml for an atom?
ml = orbital orientation = electron's "room" in house ml = -l → +l
For one n level, how many p orbitals are there? How many electrons total can there be in all the p orbitals?
• 3 orbitals per n: x, y, and z axes • Dumbbell shaped, aligned along x-axis, y-axis, or z-axis • Can exist perpendicular to e/o on x, y, and z axes • Per n level: 3 orbitals * 2 electrons/orbital = 6 electrons total
For one n level, how many d orbitals are there? How many electrons total are there in all the d orbitals?
• 5 orbitals per n: exist in five different planes • Each d-orbital occupies an entire plane • Per n level: 5 d orbitals * 2 electrons/orbital = 10 electrons total
For one n level, how many f orbitals are there? How many total electrons are there in all the f orbitals combined?
• 7 f-orbitals per n-level • Per n-level: 7 f orbitals * 2 e-/orbital = 14 e-s total
Find the Rate Law for the multistep reaction: 2H₂ + 2NO → 2H₂O + N₂ That has the steps: 1. NO + NO ⇌ N₂O₂ (fast) • Forward rate constant = k₁ • Backward rate constant =k₋₁ 2. N₂O₂ + H₂ → H₂O + N₂O (slow) • Rate constant = k₂ 3. N₂O + H₂ → N₂ + H₂O (fast) • Rate constant = k₃
• First, write rate law using the slow, rate-limiting step: • Rate = k₂[N₂O₂][H₂] • Problem: The rate law includes N₂O₂, which is an intermediate produced in the first reaction. • Rate laws cannot contain intermediates. They can ONLY CONTAIN REACTANTS from the overall reaction. • To solve the problem: Write rate law, expressing the [intermediate] using only reactants: • Use the definition of equilibrium for the first step: • In equilibrium: Rate of forward reaction = Rate of backward reaction • k₁[NO]² = k₋₁[N₂O₂] • Solve for [N₂O₂]: • [N₂O₂] = k₁[NO]²/k₋₁ = (k₁/k₋₁)*([NO]²) • Plug the value you found for [N₂O₂] back into the initial rate law you wrote: • Rate = k₂[H₂]*((k₁/k₋₁)*[NO]²) • Define a new rate constant to simplify the rate law: • Answer: • Rate = k[H₂][NO]² • k = (k₂*k₁)/k₋₁
For one n level (electron shell), how many s orbitals are there? How many electrons total are there in all the s orbitals?
• One s-orbital per n: a sphere at the origin • Simplest • Sphere shaped • One orbital (of any kind, not just s) holds two electrons • Per n level: 1 s orbital * 2 electrons/orbital = 2 electrons