Chemistry 2
What is an example of environment that has constant volume? What about constant pressure?
Constant volume: system confined by rigid walls (metal box) Constant pressure: system open to the atmosphere (a cup)
What are the three types of heat exchange? What are their definitions?
Convection: fluid movement cased by hotter portions of fluid rising and the cooler portions of fluid sinking Radiation: electromagnetic waves emitted from a hot body into the surrounding environment Conduction: molecular collisions carry heat along a conduit -heat conduction = current flow through a wire
What is specific heat capacity? What are the units? What is the formula? What do the variables stand for? What's the specific heat of water?
Energy absorption for one individual substance only. Unit: per unit mass c = q/m*delta T or q=m*c*delta T c = specific heat q = heat m = mass T = temperature 1.0 cal/g*Celsius or 4.18 J/g*Celsius
What is the first law of thermodynamics? How is the sign of work defined in chemistry? In physics?
Energy can be neither created nor destroyed. Chemistry: work done by the system = (-) work done on the system = (+) Physics: force and displacement in the same direction = (+) force and displacement in opposite directions = (-)
If ∆H is positive and entropy change is negative, what will the sign of ∆G be?
Enthalpy = + = unfavorable change Endothermic = energy will be needed to move reactants into products Entropy = - = unfavorable change, more order Gibbs free energy will more than likely be positive and not spontaneous.
What is ΔHvaporization? What is the reverse reaction?
Enthalpy associated with the phase change of a liquid to a gas Reverse: Condensation - gas to a liquid - change the sign of ΔH
What is ΔHfusion? What is the reverse reaction?
Enthalpy associated with the phase change of a liquid to a solid Reverse: Melting - solid to a liquid - change the sign of ΔH
What is ΔHcombustion? What does a high ΔHcombustion mean? What about a low ΔHcombustion?
Enthalpy for the combustion of a compound with O2 to form CO2 + H2O high heat of combustion = unstable molecule low heat of combustion = stable molecule
What is ΔHformation? If it's negative, what does that mean? If it's positive?
Enthalpy for the formation of a compound from its elements. (-) ΔHformation = exothermic (+) ΔHformation = endothermic
What is enthalpy? What can you use enthalpy to calculate? What are the units?
Enthalpy is the energy contained within chemical bonds. You can use this to find the difference in total bond energy between the products and the reactants. Units: J
What is ΔHsolution?
Enthalpy value associated with the dissolution of a species into solution
Buffer problem mnemonic:
Equally - equimolar Cold - conjugates Wizards - weak acids/bases Read - resistance Her - half-equivalence pKa - pH = pKa AHA!!! - ratio [HA]/[A-] or [A-]/[HA]
T/F An aqueous solution with a pH of 8 is basic and therefore by definition it does not contain any unreacted H+ ions.
False. It still contains a small amount of H+ ions. pH = -log[H+] = 1.0 x 10^-8 M H+
How is the pH scale ranked?
Not ranked on acids/bases themselves, but rather on how they influence the ionization of water
What happens when the salts of WA/WB dissolve in water?
One of the ions will undergo hydrolysis to re-form the WA or WB. Na2CO3 —> 2 Na+ + CO3 2- CO3 2- + H2O —> HCO3- + OH-
What's the formula for PV work? What must remain constant? What does a change in volume mean? On a graph, where is PV work found?
PV Work = P*delta V Requires constant pressure. Any change in volume tells you that PV work is being done. On a Pressure vs. volume graph, PV work is the area under the curve. A coffee cup calorimeter allows for constant pressure and therefore PV work.
What is the definition of work in physics? In chemistry?
Physics: work is energy transfer via a force Chemistry: work is energy transfer via a change in volume at constant pressure
What is the third law of thermodynamics?
Pure crystalline substances (perfect solids) at absolute zero have an entropy of zero.
What happens to energy availability as a reaction proceeds and randomness increases? What if randomness decreases?
Randomness increases: Entropy increases and energy will be released. Energy is available to do work. Randomness decreases: Entropy decreases and energy is required to "create" this increased order (liquid —> solid). Energy is used to create increased order and it thus not available to do work.
If a question states: "A strong base is titrated with a strong acid," which one is being added drop- wise and which one is in the beaker? Which solution is referred to as the titrant? Which solution is referred to as the anylate?
SB = in the beaker —> analyze SA = added drop wise —> titrant
What does "salt of a weak acid" mean? Give an example. What about "salt of a weak base"?
Salt of a WA: conjugate base of that WA + cation WA = HCO3- Conjugate base = CO3 2- Salt of a WA = Na2CO3 Salt of a WB: conjugate acid of that WB + anion WB = NH3 Conjugate acid = NH4+ Salt of a WB = NH4NO3
Acid HX dissociates 80% in water. Would you expect its Ka to be greater than, less than, or equal to one?
Since the reaction almost fully dissociates, the ratio of products/reactants is greater than 1. An acid with a Ka > 1 is classified as a strong acid.
What is standard state? What is the enthalpy of elements in standard state? Why?
Standard state is a set of specific conditions chosen as a reference point for measuring and reporting enthalpy, entropy, and Gibbs free energy. When values are given under these conditions, delta H has a know above it (degree sign). DON'T MEMORIZE STANDARD STATE VALUES!!!!!!!!!!!! Delta H formation = 0 for elements in their standard state because these elements are used to define the enthalpy scale and thus there will be no change in energy to create them from themselves. If you break the bonds of the element in it's standard state, then delta H will move. DELTA H AND DELTA H FORMATION ARE DIFFERENT.
What is the one thing that changes Keq?
Temperature
First Law Thermo Mnemonic:
delta E = q + w Eminem Questioned Wiz about work
What is temperature? What is an equation that shows the linkage between kinetic energy and temperature? How do you convert Celsius to Kelvins?
Temperature is the measure of the average kinetic energy of the molecules in a substance. KE = (3/2)*kb * T kb = Boltzmann's constant Celsius + 273K = ______K
The conjugate base of a strong acid is usually a weak base. Therefore, it can also be said that the Kb of the conjugate base of a strong acid compares in what way to the Kb of a strong base?
The Kb of the conjugate will be less than the Kb of the strong base.
What is heat capacity? What are the units? What is the formula? What do the variables stand for?
The amount of energy (J or cal) a SYSTEM must absorb to give a unit change in temperature (J/k or cal/Celsius) C = q/delta T C - heat capacity q = heat (or other energy) T - temperature
What is Gibbs free energy? What makes it negative? Positive? Units?
The amount of free energy or useful energy available to do work. -G: free energy is available to do work, spontaneous reaction +G: no free energy is available, energy is requires, not a spontaneous reaction
Explain why HF is NOT a strong acid and yet the closely related HCl is a strong acid?
The difference is a matter of structure. When looking at their conjugate bases, F- is far less stable than is Cl- due to its smaller size. When a smaller molecule has to bear a full formal charge it experiences a greater charge density and therefore more instability. A larger atom such as chlorine can spread out this charge over a greater area.
What is ∆Hrxn? How do you go about calculating it?
The enthalpy change for a reaction. It's calculated by adding the reactions (their enthalpy values) together from an enthalpy table. This will result in the net reaction for ∆Hrxn. You must change the sign of ∆Hrxn if the reaction proceeds in the opposite direction.
If a given reaction has a negative Gibbs Free Energy, what is true?
The reaction is spontaneous The absolute value of the free energy of the products exceeds that of the reactants Keq is greater than 1 - this is proven by the equation ∆G = -RTlnK because if ln(K) is less than 1 would result in a positive ∆G
If there were no change in randomness during the reaction, what would happen to Gibbs free energy and enthalpy? What would happen if entropy increases? Think: fundamental thermodynamic relation
They would be equal. ∆G = ∆H ∆G = ∆H - T∆S Increase ∆S = energy will be released and that energy (along with ∆H) will be available to do work. This will create a more negative ∆G. Decrease ∆S = energy will be used to create this increased order and less energy will be available to do work. ∆G will decrease (go more positive).
Predict the various pH's with relevance to 7 under the following titrations: WB w/ SA: WA w/ SB: SA w/ SB: WA w/ WB:
WB w/ SA: pH < 7 WA w/ SB: pH > 7 SA w/ SB: pH ~7 WA w/ WB: pH ~7 **assuming equal strength; these titrations are rarely attempted
Based on pKa and Ka, how do you classify a weak acid? What about a weak base?
Weak Acid: pKa > 0 Ka < 1 anything not on the SA list Weak Base: pKb > 0 Kb < 1 anything not on the SB list
What is PV work?
Work necessary to increase volume
How many equivalents of base can be neutralized by one equivalent of H2SO4?
2 equivalents of base neutralized
What is the reaction for base dissociation? What does Kb equal?
A- + H2O —> OH- + HA Kb = [OH-][HA]/[A-]
Hydrolysis of which of the following salts in solution will increase the pH of the solution? a) NaNO2 b) NH4Cl c) NaF d) NaClO2 e) CH3COONa f) NaCl
A. HNO2 + OH- = Increase pH B. NH3 + H3O+ = Decrease pH C. HF + OH- = Increase pH D. HClO2 + OH- = Increase pH E. CH3COOH + OH- = Increase pH F. HCl + OH- = Increase pH
For which of the following titrations will the [OH-] = [H+] at the equivalence point? For which titrations will [titrant] = [analyte] at the equivalence point? a) SA with SB b) WB with SA c) WA with SB d) WA with WB
A. [OH-] = [H+], [titrant] = [analyte] B. [OH-] doesn't equal [H+], [titrant] = [analyte] C. [OH-] doesn't equal [H+], [titrant] = [analyte] D. [OH-] doesn't equal [H+], [titrant] = [analyte] [OH-] = [H+] ONLY happens in strong/strong titrations [titrant] = [analyte] happens at ALL titrations
According to the first law of thermodynamics, if 10J of heat were transferred to the system and 10J of work were also done on the system by the surroundings, what would energy of the system and surroundings be according to definitions 1 and 2?
According to definition 2, ∆E = 10J + 10J = 20J. According to definition 1, ∆Esystem = 10J + 10J = 20J and ∆Esurroundings = -10J + (-10J) = -20J. Therefore ∆Eisolated system = 20J - 20J = 0.
The conjugate base of Acid A has a Kb of 1.0 x 10-9 and the conjugate base of Acid B has a Kb of 1.0 x 10-10. Which acid will create the largest decrease in pH when added in equimolar amounts to pure water?
Acid B will give the largest drop in pH. The smaller Kb represents the stronger acid (because Ka and acid strength are directly related) based on the formula Kw = Ka*Kb where Ka and Kb are inversely related.
Which of the following substances would be expected to have the greatest specific heat capacity? A. Water B. Steel C. Methane D. Benzene
Answer: A If both had been sitting outside for several hours on a hot 110 degree day, what would you rather put your hand on, a pot of water or a steel plate? Water resists changes in temperature and stays cooler, meaning it has the highest specific heat capacity.
What's the difference between Arrhenius, Broasted-Lowry, Lewis, Conjugates, and Amphoteric acids/bases?
Arrhenius: **not common on MCAT - acids produce H+ ions in solution - bases produce OH- ions in solution Bronsted - Lowry: **COMMON ON MCAT - acids donate protons (H+) - bases accept protons (H+) Lewis: **MCAT will specify if it's Lewis, seen on test - acids accept a pair of electrons (AlCl3, BF3) - bases donate a pair of electrons (NH3, OH-) Conjugates: - conjugate base (Cl-) : acid (HCl) - conjugate acid (NH4+) : base (NH3) Amphoteric: - substances can act as either an acid or a base (H2O)
The hydration of ammonium nitrate is a highly exothermic dissolution reaction. Which of the following statements is NOT true of this process? A) The reaction must be spontaneous because it is both exothermic and has a favorable entropy change. B) The reaction could be spontaneous or non-spontaneous depending on the temperature at which the reaction is run. C) The products of the reaction have greater entropy than do the reactants. D) The total bond energy of all the products exceeds the total bond energy of all the reactants.
B
If a reactant is dissolved in solution, causing the temperature of the reaction vessel to increase, the G for this reaction must be
+ entropy = favorable, solid to liquid increased temperature = heat given off = exothermic = - enthalpy G will be negative = spontaneous
What does positive entropy mean for randomness and energy? What does negative entropy mean?
+S: increase randomness and more energy is available to do work. Examples: solid to liquid, liquid to gas -S: decrease randomness and less energy is available to do work. Examples: gas to liquid, liquid to solid
Do light or dark colors absorb more heat? Which one radiates more heat?
-light colors absorb less and radiate less -dark colors absorb more and radiate more
Thermo laws mnemonics:
0th: Let's keep score - everything will eventually level out and reach the same equilibrium temperature 1st: You can't win - no matter how much work you put in, no energy will ever be created 2nd: You can't break even - you can't get all of the energy out of the water dam 3rd: You can't leave the game - the purest crystalline substances with the lowest entropy's have an entropy of 0
What is the second law of thermodynamics?
1. Entropy (chaos) in an isolated system can never decrease. 2. Heat can't be changed completely into work in a clyclical process. Heat can be completely converted into work in a single process, but continuous conversion of heat into work requires a cyclical process (a heat engine). All attempts to construct a 100% efficient heat engine have failed. You must lose some energy (a small amount) in order to have a cyclical process.
What all increases when entropy increases? (4)
1. Number of particles/items/etc. gas>liquid>solid If 2 moles of reactant (not gas) turn into 1 mole of product gas, entropy has increased. 2. Volume 3. Temperature 4. Disorder (entropy is greater for amorphous material than crystal) 5. Complexity (entropy is greater for C2H6 than CH4)
What are the two common ways to define the first law of thermodynamics? How do these mean the same thing?
1. total energy of an isolated system is always constant 2. energy change in a closed system is equal to the heat absorbed by that system plus and work done on that system by its surroundings delta E = q + W Definition 2 treats the system and its surroundings separately. The total energy change could be calculated by adding the work done on the system and energy absorbed. If definition 2 would assume that the system and surroundings are the same thing, we would get an isolated system (definition 1). The entire isolated system wouldn't change in energy, which is what definition 1 states. What were formerly considered the "system" and the "surroundings" in definition 2 are now just parts of the "system" as defined for definition 1.
Name the 7 ways to recognize a buffer.
1. watch for equimolar amounts 2. watch for conjugates 3. watch for WEAK acids or bases 4. Watch for resistance to pH change 5. Watch for half-equivalence points 6. Watch for pH = pKa 7. Watch for the ration [HA]/[A-] or [A-]/[HA]
Beaker A contains 2.55 g of FeCl3 dissolved in 100 mL of water. Beaker B contains 10.20 g of FeCl3 dissolved in 400 mL of water. If the specific heat capacity of the solution in Beaker A is known to be 1.33 cal/g ̊C, what is the expected specific heat capacity of the solution in Beaker B?
1.33 cal/g*Celsius same substance = same specific heat capacity
What is a calorimeter? What does it measure? What is assumed about q? What are the two types of calorimeters? Which type of calorimeter provides constant pressure and which type provides constant volume?
A calorimeter is a device used to calculate enthalpy change (delta H). It measures q. Assume the q = delta H *true at constant pressure Coffee cup calorimeter: constant pressure, measure using q=m*c*delta T (uses specific heat capacity) Bomb calorimeter: constant volume, measure using q=C*delta T (uses heat capacity) This gives the change in energy (delta U or delta E), NOT the change in enthalpy (delta H).
What is a buffer? What is the buffer region? What will happen if you add a bunch of titrant around the buffer region?
A solution that contains a weak acid and weak base, often the conjugates of each other. The nearly horizontal area surrounding the half-equivalence point. There will be little affect on pH.
How does the hydrogen ion concentration differ for two solutions, one with pH = 2 and the other with pH = 4?
A solution with a pH of 2 has [H+] = 10^-2, while a solution of pH 4 has [H+] = 10^-4. Thus the pH 2 solution has 10^2 or 100 times the [H+] of a solution with a pH of 4.
When calculating ∆Hrxn, what sign would a bond get if it's broken and you're adding up bond energies? What sign would you get if a bond is formed?
Bond is broken = (+) Bond is formed = (-)
Mnemonics for heat capacity and specific heat capacity
C a QT (see a quick trip) C = q*delta T MCAT q = m*c*delta T
Fundamental Thermodynamic Relation:
GHOSTS ∆G = ∆H - T∆S
Name all of the strong bases. (9+)
Group 1A Hydroxides** NaOH KOH NH2- H- Ca(OH)2 Sr(OH)2 Ba(OH)2 Na2O CaO
What is the reaction for the ionization of water? What are the three main formulas used for this?
H2O + H2O —> H3O+ + OH- (H3O+ is the same as H+) Kw=[H3O+][OH-]=10^-14 @ 25 Celsius pKw = pH + pOH = 14 pKa + pKb = 14
What is the reaction for acid dissociation? What does Ka equal?
HA + H2O —> H3O+ + A- (H3O+ is the same as H+) Ka = [H+][A-] / [HA] **H2O is omitted because it's a liquid
Which of the following is not a strong acid? HCl, HBr, HF, HI
HF
Assuming that all species in Table 1 will combust when burned with O2, which of the following gives the species with the largest and smallest negative heats of combustion, respectively? F2 bond energy = 150 HF bond energy = 600 A. HF and F2 B. F2 and HF
HF is more stable because it has a higher bond energy than F2. In heat of combustion, all bonds are broken which means the higher energy = the higher combustion = less stable the molecule. Since F2 is less stable than HF, it will have a higher heat of combustion. Answer: B
Name all of the strong acids. (8)
HI HBr HCl HNO3 HClO4 HClO3 H2SO4 H3O+
What happens when heat enters a system? Does the temperature always increase? Is any increase in temperature always exactly proportional to the heat absorbed by that system?
Heat a sealed balloon: gases inside expand and do work on the rubber walls of the balloon and air around it to accomplish this expansion. Only the remaining energy not used for PV work (increase volume) will go toward increasing the average kinetic energy of the molecules (increase temperature). System capable of volume change: heat can go to PV work, increasing the temperature, or both. The addition of a certain amount of heat won't necessarily be exactly proportional to the resultant increase in temperature. System not capable of volume change: all heat will go toward increasing the temperature
Will the heat capacity be greater for a system with constant volume or a system with constant pressure?
Heat capacity will be larger for constant volume than constant pressure because volume takes PV work into consideration, which takes away energy from increasing the temperature. Small change in temperature = larger heat capacity Large change in temperature = small heat capacity ***inverse relationship
Beakers 1 and 2 contain 0.25 L of water and 0.5 L of water, respectively. How does the heat capacity of the water in Beaker 1 compare to that of the water in Beaker 2? How do the specific heat capacities compare?
Heat capacity: 0.5L of water will have a higher C because it experiences a smaller change in temperature Specific heat capacity: exact same for both since they're the same substance
What's the difference between specific heat capacity and heat capacity? Difference between units?
Heat capacity: energy absorbed for a system. A system can include the solution, the container holding the solution, and the thermometer in the solution. Unit: cal/Celsius or J/K Specific heat capacity: energy absorbed for one individual substance. This could be the individual solution or the individual container holding the solution. Unit: cal/g*Celsius or J/g*Celsius
What does a high positive bond energy mean? What does a large negative heat of formation mean?
High positive bond energy: very stable Large negative heat of formation: amount of energy released when the compound is formed is high - the compound is very stable
How do you calculate pH for WA?
ICE Table: Calculate the pH of a 1.00 M solution of CH3COOH (aq.) CH3COOH + H2O —> H3O+ + CH3COO- I 1.00 0 0 initial C -X +X +X change E 1.00-X +X +X equilibrium Ka = [H3O+][CH3COO-] / [CH3COOH] Ka = (X)(X) / (1-X) = 1.8 X 10^-5 (given) 1.8 X 10^-5 = X^2/1 X = [H3O+] X = 0.0042 pH = -log[H3O+] pH = -log (0.0042) pH = 2.38
What does the zeroth law of thermodynamics state?
If object A is in thermal equilibrium with object B, and object C is also in thermal equilibrium with object B, then objects A and C must be in thermal equilibrium with each other. Everything tends to move toward thermal equilibrium with everything else. Objects with higher temperatures will always equilibrate over time with their surroundings, including other objects with which they are in contact. Finally, if two objects are in thermal equilibrium, by definition they have the same temperature.
A pan of water is placed upon an electric heating element on a stove. Describe all types of heat exchange expected to occur in this scenario.
If the pot and water are at the same temperature, no heat exchange will occur. If the pan is hotter than the element (say the element isn't even turned on yet), then heat flow will occur in the opposite direction to that most students will propose. Assuming the pot is cold and the heating element is hot: Heat will be transferred from the element to the pan via conduction because they are in contact with one another. Heat will be transferred from the pan to the water via conduction because they are also in contact with one another. The water in the bottom of the pan will heat up first and that will cause this hotter part of the liquid to rise while the cooler liquid above sinks—which is convection. Finally, any part of the system that is hotter than the environment will radiate heat into the air— including the heating element itself, the pan, and the water.
Can energy be used to increase temperature in a fundamental thermodynamic relation?
No. Normally energy can be used to increase temperature or expand the volume. However, the fundamental thermodynamic relation has an isobaric/isothermal reaction. Therefore, an increase in temperature or PV work isn't conducted.
SA mnemonic:
Injured - HI Babies - HBr Chewed - HCl Nannies - HNO3 Cloved - HClO4 Clothes - HClO3 So - H2SO4 Hopefully - H3O+
What are definitions for isobaric and isothermal?
Isobaric: constant pressure Isothermal: no heat exchange (constant temperature)
What's the difference between an isolated system and a closed system?
Isolated: neither mass nor energy can be exchanged with the surroundings Closed: the system can exchange energy with its surroundings but not mass
What are the units for watts?
J/s
If the value of Keq is known, what can we infer about ΔG°? If a reaction is spontaneous, what can we infer about the rate of that reaction?
K > 1 = spontaneous K < 1 = not spontaneous K = 1, G = 0 because ln(1) = 0
What is a formula showing the relationship between Ka and Kb?
Ka*Kb = Kw = 10^-14 @25 Celsius ([H+][A-]/[HA])*([OH-][HA]/[A-]) = [H+][OH-] = Kw
What are some equilibrium constants? By what law are they written? What is omitted?
Keq, Ka, Kb, Kw, Ksp Written by the law of mass action Pure liquids and solids are omitted.
If Ka is large, what is pKa? What does this mean? What about a large Kb?
Large Ka = small pKa = more products than reactants = lots of H+ formed = very strong acid Large Kb = small pKb = very strong base, lots of OH- formed
What is the relationship between delta Hcombustion and stability?
Largest negative delta Hcombustion = least stable
What is entropy? What happens if entropy increases? What are the units?
Measure of randomness/disorder/chaos in a system If entropy increases, the reactions will be more likely to be spontaneous. Units: J/K
What is the half equivalence point?
Mid-point of the nearly horizontal section of the graph [HA] = [A-] HA will continue to be deprotonated until it reaches the equivalence point (vertical section) where the solution contains 100% A- and 0% HA. THIS ISN'T TRUE OF SA/SB because they dissociate 100%. SA/SB DON'T HAVE HALF EQUIVALENCE POINTS!!!!!!! because immediately after adding HA, 100% of the solution will have turned to A-
What is the equivalence point of a SA/SB? What is the correlation between the titrant concentration and the analyte concentration? What is the correlation between H+ and OH- in titrations with SA/SB? What is the equivalence point of SA/SB titrations?
Mid-point of the nearly vertical section of the graph. [titrant] = [analyte] Titrations with SA/SB = [H+] = [OH-] pH = 7 for all SA/SB titration equivalence points
What is the equivalence point of a WA w/ SB or WB w/ SA? What is the correlation between the titrant concentration and the analyte concentration? What is the correlation between H+ and OH- in titrations with SA/SB? What is the equivalence point of SA/SB titrations?
Mid-point of the nearly vertical section of the graph. [titrant] = [analyte] [H+] = [OH-] because WA/WB don't dissociate 100%..........can tell automatically that pH doesn't equal 7!!!!
Conduction
Natural flow from hot to cold due to two things being in contact with one another
How do you calculate pH for a SA/SB?
pH = -log [SA] pOH = -log [SB] We assume that the molar concentration of the acid or base is equal to the molar concentration of hydrogen ions or hydroxide ions. This can't be true because some of both of these ions (10-7M) are already present in water before addition of the acid or base. The assumption is usually safe because the molar concentration of the strong acid or base is usually many magnitudes larger than 10-7. We are also assuming that the acid and base dissociate 100%. If only 75% of the acid dissociated in solution—this would be a significant difference in concentration compared to 100% dissociation. Assuming that very strong acids dissociate 100% is usually a safe assumption, although ion-pairing and other factors due reduce the effective concentration of ions.
What are the 3 major pH equations?
pH = -log[H+] pOH = -log[OH-] pH + pOH = 14
What is the Henderson - Hasselbach equation? Prove that pH = pKa at the half - equivalence point.
pH = pKa + log[A-]/[HA] At the half-equivalence point, [HA] = [A-] which gives a ratio of A-/HA = 1 pH = pKa + log(1) pH = pKa + 0 pH = pKa
Three common indicators used in the lab are methyl orange, litmus, and phenolphthalein. These indicators change color at a pH of 3.7, 6.5, and 9.3, respectively. Which indicator should be chosen to identify the equivalence point for the titration of a weak acid with a strong base?
phenolphthalein = 9.3 WA with a SB = higher than 7 equivalence point
Draw 4 titration curves: 1. SA titrated with SB 2. SB titrated with SA 3. WA titrated with SB 4. WB titrated with SA
see notes
What is waters role in maintaining homeostatic temperatures in the human body?
specific heat capacity
If the change in entropy is positive, and enthalpy is negative, the reaction is ____________.
spontaneous + entropy = favorable - enthalpy = unfavorable
What does heat of combustion measure? What do smaller negative heats of combustion mean for stability? What do larger negative heats of combustion mean for stability?
stability Small negative: more stable Large negative: less stable
What does one equivalent mean?
the amount of acid/base necessary to produce/consume one mole of [H+] ions
What are indicators? How do you choose an indicator? What is the end point?
weak acids that change color as they dissociate from HA into H+ and A- In order to choose the correct indicator, you need to know the approximate pH of your equivalence point and then select an indicator that will change color at that approximate pH. The end point is when the indicator causes a color change. There's no relationship between the color change (equivalence point) and the end point
What formula relates the equilibrium constant to the Gibbs free energy?
∆G° = - RTlnKeq **ln(any + number less than 1) = (-)