Chapter 13 and 14
What is a Unsaturated solution?
A solution whose concentration is lower than the solubility limit for a given temperature
How do you reach equilibrium in a gas solution?
equilibrium is reached when the concentration of gas dissolved in the solvent is high enough that the rate of gas molecules escaping the solution again equals the rate of gas molecules entering the solution
Describe the overall process on finding the Rate Law by Inspection.
*When finding order you only compare experiments that have a reactant with a constant concentration (the unchanging one is then solely responsible for the change in rate) *The change in Concentration (M) gives the base of your derivative (i.e. 2^x) and the change in rate will dictate your exponent and therefore power (i.e. Δ[x] of 2^x but rate doubled so exponent is 1 and order is 1)
Describe the overall process on finding the Rate Law via the Method of Initial Rates.
-First you must find the Rate Law -Pick two experiments for which you will use to compare (Ex: say you pick experiment 3 and 1) so plug in your data into the general Rate Law for the equaton and put experiment 3 data over your data for experiment 1 and solve (remember to cancel things out) *Remember to use log to bring down an exponent once you get to the point where you are left with something like 2 =2^x with log would be log(2) = x log(2) **If none of the reactants are constant then you do this for both if not then you can use the method of inspection for one
3. How does Temperature affect solubility?
-The solubility of all gases in water decreases with increasing temperature -The solubility of most ionic compounds increases with increasing temperature
What are the three types of rates?
1. Initial Rate 2. Average Rate 3. Instantaneous Rate
-What are the two enthalpy changes that occur in a solution?
1. KF(s) → K⁺(g) + F⁻ (g) (Seperation of ions) Energy must be supplied to separate the ions in the lattice against their attractive forces -∆latticeH (ions seperated) -highly endothermic 2. K⁺ (g) + F⁻ (g) → K⁺ (aq) + F⁻ (aq) (solvation of ions) Energy is evolved when the individual ions dissolve in water, where each ion becomes surrounded by water molecules ∆hydrationH -strongly exothermic.
What are the three defining characteristics of most colloids?
1. Many of the substances that form colloids have high molar masses 2. The particles of a colloid are relatively large -leads to Tyndall effect 3. Even though colloidal particles are large, they are not so large that they settle out.
-What three factors affect solubility? Which affect solubility of gases in liquids? solids in liquids?
1. Solute-solvent interactions 2. Pressure (affects only gases in liquids) 3. Temperature (affects both gas and solids in liquids)
--According to the Collision theory of reaction rates, what are the three conditions that must be met for a RXN to occur?
1. The reacting molecules must collide with one another. 2. The reacting molecules must collide with sufficient energy to initiate the process of breaking and forming bonds. 3. The molecules must collide in an orientation that can lead to rearrangement of the atoms and the formation of products. (reactive vs non-reactive RXNs)
What two words did we get from Graham's conclusion on colloids?
1."Sol" -for a colloidal dispersion of a solid substance in a fluid medium 2. "Gel" -for a colloidal dispersion that has a structure that prevents it from being mobile
-What does the graph of a second order RXN look like? (give the equation and what your x & y would be)
1/ ln[R] vs t (yields straight positive line)
What is the Integrated second order Rate Law equation?
1/[x] - 1/[x]₀ = kt where: [x]₀ is the initial concentration at t=0 [x] is the current concentration t=time k= rate law constant
Ch. 13
Solutions and Their Behavior
What is the Rate determining step (rds) of a RXN?
A RXN can proceed no faster than the slowest step in the RXN mechanism
How do you know if you have a catalyst in a RXN?
A catalyst is added to a reaction to increase its rate. It is consumed in an early step, but is generated in a subsequent step so that it does not appear as a reactant in the overall equation for the reaction. *Shows up at beginning as reactant, ends as product
How do you know if you have a RXN intermediate?
A reaction intermediate appears as a product in one step, but is consumed in a subsequent step, so that it does not appear as a product in the equation for the overall reaction *shows up in between as product but never is in final
What is a Saturated solution?
A solution whose concentration is at the solubility limit for a given temperature *rate of dissolving is equal to the rate of crystallization
What is a Supersaturated solution?
A solution whose concentration is greater than the solubility limit for a given temperature -are unstable -the excess solid eventually crystallizes from the solution until the equilibrium concentration of the solute is reached -exothermic
-What is an Integrated Rate Equation? What are its uses?
An equation relating the concentration of a reactant to its initial concentration and the elapsed time -can be used to find initial concentration, a desired concentration or the time to reach a concentration (given proper information)
What is an emulsifying agent?
a substance which stabilizes an emulsion by increasing its kinetic stability
Ch. 14
Chemical Kinetics: The Rates of Chemical Reactions
How does Temperature affect the RXN Rate?
Chemical reactions occur more rapidly at higher temperatures (generally true)
-What are Colligative Properties? Which four are we covering?
Colligative properties are the physical changes that result from adding solute to a solvent. Colligative Properties depend on how many solute particles are present as well as the solvent amount, but they do NOT depend on the type of solute particles. 1. Vapor pressure lowering (using Rault's law) 2. Boiling point elevation (∆Tbp) 3. Freezing point depression (∆Tfp) 4. Osmotic pressure (π)
What affects the RXN rate of chemical reactions? (four things)
Concentration Temperature Catalysts Surface area of a solid
-What is an Elementary step? (aka Elementary RXN)
Each step in a multistep reaction sequence is an elementary step -defined by a chemical equation that describes a single molecular event such as the formation or rupture of a chemical bond resulting from a molecular collision
*How does sickle cell anemia happen?
First "molecular" disease -Hemoglobin (Hb) -Normal Hb: glutamic acid, polar side chain -Abnormal Hb: valine, nonpolar side chain Nonpolar side chain decreases solubility of Hemoglobin in blood
How does Concentration affect the RXN Rate?
If the concentration of a reactant is increased, the reaction rate will increase as well (generally true)
What is a Catalyst?
Lowers Ea -Proceeds by a different mechanism (alternative pathway) -Catalyst is not consumed *Overall stoichiometry unchanged, only meachanism is changed ∆rxnH is unchanged
2. What is molality (m)? What are the units?
Molality is often used as the concentration unit involved in calculations dealing with colligative properties, such as freezing point depression, boiling point elevation and osmotic pressure moles of solute (mol) per kilogram of solvent (kg) m = moles of solute/kg of solution
1. What is molarity (M)? What are the units?
Molarity is the most common concentration unit involved in calculations dealing with volumetric stoichiometry. moles of solute (mol) per liter of solution (L) M = moles of solute/L of solution
Example: What would be the balanced RXN Rate for the decomposition of H₂O₂ in the following RXN? 2H₂O₂ → 2H₂O + O₂
RXN Rate = ∆[O₂]/∆T = −1/2 (∆[H₂O₂]/∆T) Because 2 mole of H₂O₂ disappears for each mole of O₂ that forms, the rate of disappearance of H₂O₂ is twice the rate of appearance of O₂. To equate the rates, we must divide the rate of disappearance of H₂O₂ by 2 (its coefficient in the balanced chemical reaction) therefore leaving 1/2 and the negative coming from its disappearance (reactant)
RXN Rate vs Rate law:
RXN Rate does NOT have k or the order (power) Rate law has k and the order of a RXN
Algebra tip to keep in mind when solving for a k
Remember that in the Arrhenius equation when solving for a k you must separate them by distributing the ln (so you end up with ln k₁ - ln k₂ )
*Why is the 0th order RXN special?
Special because the rate law constant for a zero order RXN is = to the rate (has same units)
What is a surfacant?
Substances such as soaps that affect the properties of surfaces, and therefore affect the interaction between two phases Ex: emulsifying agent, detergent
1. What is Raoult's Law?
Summarizes that the vapor pressure of a pure solvent is REDUCED when a nonvolatile solute is added Psolution = Xsolvent x Pºsolvent Psolution = the vapor pressure of the solvent over the solution (overall) Pºsolvent = the vapor pressure of the pure solvent Xsolvent =the mole fraction of the solvent
What is the ∆E?
The amount of energy that is gained or lost *endothermic RXN if positive (products have more E) *exothermic RXN if negative (producst have less E)
--What is Solubility?
The maximum amount of a solute that will dissolve in a given amount of solvent at a given temperature is called the solubility of that solute in that solvent at that temperature Ex: Solubility of CuCl₂, for example, is 70.6 g in 100 mL of water at 0 °C. If we add 100 g of CuCl₂ to 100 mL of water at 0 °C, we can expect 70.6 g to dissolve, and 29.4 g of solid to remain
--What is the Rate Law?
The resulting relationship between reactant concentrations and reaction rate Ex: rate = k[N₂O₅]¹ *Only includes measurable concentrations so cannot include RXN intermediates since they are not attainable in lab to measure (are formed in between elementary steps)
What is hypotonic?
There is a net flow of water into the cell, causing the cell to swell and perhaps to burst (or lyse) Concentration of solutes outside the cell is less than that inside
What is hypertonic when reffering to the body and its cells?
There is a net flow of water out of the cell, causing the cell to dehydrate, shrink, and perhaps die Concentration of solutes outside the cell is greater than that inside
What is Isotonic?
This solution has the same molality as body fluids (the solutions are of equal pressure) Concentration is equal inside and outside so no movement of water
--What are Concentration-Time Relationships?
Uses mathematical equations to relate time and concentration
How do you find the units for k?
Using this format: M/s = kM^to a given order Ex: Give the 1st order units: M/s = kM¹ so you divide by M (which gets canceled out) k=1/s
2. What is the Average Rate?
We calculate the average rate of a reaction over a time interval by dividing the change in concentration over that time period by the time interval
*What is the rule with hydrocarbons/polar molecules and their solubility in water?
When the hydrocarbon end is small, the -OH (or any polar end) dominates and solubility in water is high. -Polar molecules with fewer than 4 carbon atom chains are miscible with water. -After that, as the length of the carbon chain increases the solubility in water decreases.
When there is a Chemical RXN with multiple steps, how do you determine/what do you base your Rate Law off of?
You base it off of the rate determining step (slowest) RXN cannot go faster than the slowest step
How do you solve for the order of a RXN if you have a compound that is not solavable via the method of inspection?
You have to use the Method of Initial Rates
How do you read a RXN Rate equation?
You must keep in mind that coefficients were originally divided to get the rate since you are looking at the way one mole disappears Ex: 2 NO(g) + Cl₂(g) → 2 NOCl(g) Cl would have a coefficient of -1, NO would have a coefficient of -1/2 and NOCl would have a coefficient of 1/2 (Cl dispersal twice as fast)
-What does the graph of a zero order RXN look like? (give the equation and what your x & y would be)
[x] = -kt + [x]₀ y = mx + b plot [x] vs time
What is the Integrated zero order Rate Law equation?
[x]₀ - [x] = kt where: *[x]₀ is the initial concentration at t=0 *[x] is the current concentration *t=time *k= rate law constant
What is Solvation? What is the rule as far as polarity of solutes/solvents and whether they dissolve or not?
a process by which solutes dissolve in solvents -Hydration = term used when solvent is water "Like dissolves like" (applies to solids too) -Polar solvents dissolve polar solutes -Non-polar solvents dissolve non-polar solutes
What is Concentration (c)? What are the 4 different units of concentration we covered?
amount of a solute present in a solution per standard amount of solvent 1. molarity (M) 2. molality (m) 3. parts per million (ppm) 4. parts per billion (ppb)
What is reverse osmosis? What are its uses and how is it reached?
another method of obtaining freshwater from seawater or groundwater (membrane serves as filter) -pressure greater than the osmotic pressure of the impure water is applied to force water through a semipermeable membrane from a region of high solute concentration to one of lower solute concentration, that is, in the reverse direction that the water would move by osmosis.
-What is a hydrophilic colloid?
are strongly attracted to water molecules -often have groups such as -OH and -NH₂ on their surfaces -form strong hydrogen bonds to water, thereby stabilizing the colloid
How can Colloids with water as their dispersing medium be classified?
as hydrophobic or hydrophilic
1. How do Solute-solvent interactions affect solubility?
as stated earlier, like dissolves like
What is the Transition state?
at the transition state, sufficient energy has been concentrated in the appropriate bonds; bonds in the reactants can now break, and new bonds can form to give products -point at which E is at its max and has flat point to it
How is a hydrophobic colloid stabilized?
by positive ions adsorbed onto each particle and a secondary layer of negative ions -the particles bear similar charges, repel one another, and precipitation is prevented.
What is the Tyndall effect?
calloids scatter visible light when dispersed in a solvent, making the mixture appear cloudy
What does it mean to say two liquids are miscible?
can be mixed in any proportion to form a homogeneous mixture
What is the RXN Rate? How can it be measured?
change of a product or reactant concentration per unit of time Δ[product]/ΔT or -Δ[reactant]/ΔT (reactants go away so -) Measured experimentally by either how quickly reactants dissapear or how quickly products appear with time
How are the different types of Colloids classified?
classified according to the state of the dispersed phase and the dispersing medium
-What is an Emulsion?
colloidal dispersions of one liquid in another, such as oil or fat in water
What is the mole fraction (X)?
defined as the amount of that component divided by the total amount of all of the components of the mixture -do not multiply by 100 here, NOTasking for percent
What does it mean to say two liquids are immiscible?
do not fully mix in all proportions; they exist in contact with each other as separate layers
What is the rule of thumb for a 10 °C increase in Temperature?
doubles the rate
If a RXN has a constant half life, what order is it?
first order half life RXN
How do you find the Overall RXN order?
found when you add all the individual orders Ex: rate = k[A]¹[B]¹[C]⁰ Overall order = 1+1+0 = 2
What is a detergent?
function of a suracfant is to lower the surface tension of water, which enhances the cleansing action of the detergent
What is an Energy coordinate or "reaction coordinate" diagram? What does it tell us?
gives the E level as a RXN progresses with time -tells us Ea, Transition state, ∆E change
2. What is the Boiling point elevation (∆Tbp)?
helps find the change in boiling point after the addition of a solute
3. What is the Freezing point depression (∆Tfp)
helps find the change in freezing point after the addition of a solute
2. How does Pressure affect solubility?
higher Pressure of gas = higher solubility -pressure does not affects solid or liquid solubility
How does concentration affect the frequency of molecular collisions?
higher concentration = higher frequency
How does the Surface area of a solid affect the RXN Rate?
increasing surface area of a solid reactant = faster chemical RXN -Ex: Cutting the substance into small pieces, or grinding it into a powder *If the surface area of a reactant is increased then more particles are exposed to the other reactants*
What are the uses of the Aerhenius equation?
it can be used to: -calculate Ea from the temperature dependence of the rate constant -calculate the rate constant k, if Ea, T, and A are known. -calculate Ea from rates measured at two different Temperatures by substratcing them
What happens to a cation that exists in solution of water?
it is surrounded by the negative dipole ends of water molecules
What happens to an anion that exists in solution of water?
it is surrounded by the positive dipole ends of water molecules
What does the k in the Rate Law mean?
it is the Rate Law constant that relates rate and concentration at a given temperature -temperature dependant
-For a 1st order RXN, what are the units for k?
k =1/s
-For a 2nd order RXN, what are the units for k?
k= 1 /M × s
-For a 0th order RXN, what are the units for k?
k=M/s
*What determines the solubility of a gas in a liquid?
the partial pressure of the solute gas determines the solubility
What is the two point form of the Arrhenius equation that deals with T?
ln (k₂/k₁) = -(Ea/R) x (1/T₂ - 1/T₁) where: k2 and k1 = rate constant T2 and T1 = Kelvin temperatures Ea = activation energy R = ideal gas constant *when solving for anything on the right side of the equation plug in all values first, make sure you leave the easiest one to solve for *When solving for an ln try to solve for k₂ and rewrite the left side as ln k₂ - ln k₁
What is the Integrated first order Rate Law equation?
ln [x]/[x]₀ = -kt where: [x]₀ is the initial concentration at t=0 [x] is the current concentration t=time k= rate law constant
What equation is given if you take the ln of both sides? What are its uses?
ln k = -(Ea/R) x (1/T) + ln a y = m x + b Can be used to find the rate constant or Ea if you have the slope of a line
-What does the graph of a first order RXN look like? (give the equation and what your x & y would be)
ln[R] = −kt + ln[R]₀ y = mx + b ln[R] vs t (yields straight negative line)
3. What is parts per million (ppm)?
mass of solute over mass of solution...times 1,000,000 Ex: 1 ppm represents a solution containing 1.0 mg of a substance in a sample with a total mass of 1 kg ppm = mg of solute/kg of solution
4. What is parts per billion (ppb)?
mass of solute over mass of solution...times 1,000,000,0000 ppb = one microgram per liter (µg/L)
What is Percent by mass?
mass of solute/mass of solution
Why does solubility decrease in gases as temperature increases?
more Kinetic energy = easier for gas molecules to escape solution
How does the graph of a first order RXN look like?
negative but straight line ln [x] vs time
How does the graph of a zero order RXN look like?
negative curved line [x] vs time
What is Dissolution?
the process by which a solute forms a solution in a solvent
What is the normal boiling point of a liquid? How does vapor pressure affect it?
normal boiling point of a liquid is the temperature at which its vapor pressure is equal to 1 atm or 760 mm Hg - vapor pressure lowering leads to an increase in the boiling point
-What is a hydrophobic colloid?
one in which only weak attractive forces exist between the water and the surfaces of the colloidal particles Ex: dispersions of metals and of nearly insoluble salts in water (form precipitates)
What is a Termolecular elementary step?
one in which there are three reactants (can be same or different) -highly unlikely due to orientation Ex: 2Cl + B → something
What is a Bimolecular elementary step?
one in which there are two reactants (can be same or different) Ex: 2Cl → something or Cl + B → something
What is a Unimolecular elementary step?
one in which there is only one reactant Ex: O₂ → something or Cl → something
When there is a Chemical RXN where your rate law includes a RXN intermediate, how do you replace it? (since you can only include measurable concentration)
replace it by setting k₁=k⁻₁ (of the reversible RXN) *Do that by getting the original "fast" k (not the rds) and finding the rate law of the two reverse RXNs and setting their rate law = to each other, then solve for the intermediate...replace it into the rds rate law and make all the k's just be represented as k (like in Brosius)
--What are Colloids?
represent a state intermediate between a solution and a suspension (Particles that are suspended but not dissolved) -Dispersed phase particles distributed uniformly through a continuous phase
What is the Order of a RXN?
represented by a super scripted number and tells how rate depends upon concentration of reactants -NOT related to the stoichiometric coefficients
3. What is the Instantaneous Rate?
slope (m) of a tangent line at a certain time slope= (y₂-y₁)/(x₂-x₁) when you have two points after drawing your line
How can you find the Ea if given the slope?
slope = -Ea/R so just solve for Ea -----> Ea = -(slope × R)
-What is the RXN intermediate?
species that is first formed then consumed -cannot be attained, is in between RXN and is canceled out when elementary steps are added to find RXN mechanism
What is Le Chatelier's principle?
states that a change in any of the factors determining an equilibrium causes the system to adjust by shifting in the direction that reduces or counteracts the effect of the change
What is Henry's Law?
states that the solubility of a gas is directly proportional to the gas pressure Sg = kHPg (each has 2nd letter sub-scripted) Sg = solubility of gas (usually mol/kg) Pg = partial pressure of the gas over the solution kH = Henry's Law constant (always given in test)
What does stirring due to a solution with a solvent?
stirring prevents the build up of concentrated solvent at the surface and therefore decreases the rate of crystallization and increases the rate of dissolving
How does the graph of a second order RXN look like?
straight positive line 1/[x] vs time
What is the solute?
substance dissolved -minor component
What is the solvent?
substance doing dissolving -major component -H2O — solvent in most General Chemistry applications
What is a Catalyst and what does it do?
substances that accelerate chemical reactions but are not themselves consumed (lower the Ea required for a reaction to occur)
What is the Arrhenius equation?
summarizes the observation that RXN rates depend on the E and frequency of collisions between reacting molecules, on the temperature, and on whether the collisions have the correct geometry k = the rate constant, R = the gas constant T = the kelvin temperature *A = the frequency factor & It is related to the number of collisions and to the fraction of collisions that have the correct geometry; A is specific to each reaction and is temperature dependent. *The factor with the e = the fraction of molecules having the minimum energy required for reaction (always less than 1)
What is the half-life of a second order RXN?
t1/2 = 1/k[x]₀
What is Osmotic Pressure (π)?
the difference between the height of the solution in the tube and the level of pure water in the beaker π = cRTi or MRTi π = osmotic pressure (atm) M or c = Molarity R = gas constant (0.0821 L atm mol-1 K-1) T = absolute temperature (K) I = number of particles per formula unit
1. What is the Initial Rate?
the instantaneous rate at the start of the reaction (i.e., when t = 0) slope (m) of a tangent line at t=0
What is the weight percent?
the mass of one component divided by the total mass of the mixture, multiplied by 100
What is Activation Energy? (Ea)
the minimum energy required to initiate a chemical reaction -Ea is specific to a particular reaction. -A low Ea means fast RXN, high Ea means slow RXN
What is the mole percent?
the mol fraction times 100
4. What is Osmosis?
the movement of solvent molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration *solvent can move through the membrane *solute can't move through the membrane
What is the Molecularity of an elementary step? What three are the most common?
the number of reactants in an elementary step -whole, positive number 1. Unimolecular 2. Bimolecular 3. Termolecular
--What is the Reaction Mechanism for a chemical reaction?
the sequence of bond-making and bond-breaking steps that occurs during the conversion of reactants to products --Series of elementary steps *add elementary steps to get overall RXN stoichiometry (cancel out RXN intermediates)
-What is the rate determining step (rds)?
the slowest step in the sequence **rate law is based off of this step, NOT the overall RXN
What is chemical kinetics?
the study of how fast (Rates) chemical reactions occur
What is the enthalpy of solution?
the sum of the two enthalpy changes -The enthalpy of the overall reaction ∆solutionH = -∆latticeH + ∆hydrationH
What is the half-life of a RXN?
the time required for the concentration of a reactant to decrease to one-half of its initial value
Why is the 1st order RXN special?
the units of k (1/s) allow it to be completely independent from concentration (no M in it)
What is the half-life of a first order RXN?
t½ = 0.693/k side note: ln is applied to earlier half life equation to make it a first order and therefore independent of concentration
What is the Method of Initial Rates?
used when one or none of the compounds are constant and instead vary
What is the Rate Law order by inspection?
you find the Rate Law order by inspection by comparing experiments where one of the reagent's concentration is constant which allows you to assume the rate is affected solely by the other reagent's concentration
How is Roult's law used to find the new vapor pressure?
∆P = P°₁ - P₁ P₁ = vapor pressure of solvent in the solution P°₁ = vapor pressure of pure solvent
What is the formula for calculating the elevation of the boiling point?
∆Tbp = ∆Kbp × msolute × i solute *Where i is 1 for NONELECTROLYTES because they do not dissociate in solution -For soluble ionic solutes i equals the number of ions per formula unit *m = molality of solute K = constant of solvent
What is the formula for calculating the depression of the freezing point?
∆Tfp = ∆Kfp × msolute × i solute *Where i is 1 for NONELECTROLYTES because they do not dissociate in solution -For soluble ionic solutes i equals the number of ions per formula unit *m = molality of solute *K = constant of solvent