Exam 2
If Kc is the equilibrium constant for a forward reaction, 2A⇌B2A⇌B, what is Kc for the reaction 4A⇌2B?
(Kc)2
If Kc is the equilibrium constant for a forward reaction what is Kc′ for the reverse reaction?
(Kc)−1
Comment on the following statement: "A catalyst increases the rate of a reaction, but it is not consumed because it does not participate in the reaction."
A catalyst does participate in the reaction, but it is not consumed because it reacts in one step of the reaction and is regenerated in a subsequent step.
Which of the following changes in reaction conditions will alter the composition of an equilibrium mixture of gases for a reaction having unequal moles of gaseous products and gaseous reactants? increasing the temperature decreasing the pressure adding of reactants All of these will alter the equilibrium concentrations.
All of these will alter the equilibrium concentrations.
Which of the statements about equilibrium is correct? Reactants and products will have the same concentration at equilibrium. At equilibrium, the forward reaction and reverse reaction will have the same reaction rate. A chemical reaction stops when it reaches equilibrium. When all reactants turn into products, the chemical reaction reaches equilibrium.
At equilibrium, the forward reaction and reverse reaction will have the same reaction rate.
What are the Brønsted-Lowry bases in the following chemical reaction?
C5H5N, OH-
Which acid of the following set has the strongest conjugate base? HF H2O NH3 CH4
CH4
For Cu2+ and CO2, which will behave as a Lewis acid toward OH- in water?
Cu2+ and CO2
From the following chemical reactions determine the relative Brønsted-Lowry base strengths (strongest to weakest).
F- > H2O > NO3 -
What integrated rate law correspond with Rate = k [A]
First order
When dissolved in water, which compound is generally considered to be an Arrhenius acid?
H2S
From the following chemical reactions determine the relative Brønsted-Lowry acid strengths (strongest to weakest).
HCl > H3O+ > HCN
Which of the following Brønsted-Lowry acids does not behave as a strong acid when it is dissolved in water?
HNO2
Are reaction rates higher or lower at higher temperatures?
Higher
What is half-life independent of?
Initial concentration
how are the methods of initial rates used to determine reaction order in a reactant?
Initial rates allow the values of reactions orders to be found by running the reaction multiple time under controlled conditions and measuring the rate if reaction in each case. All variables are held constant from one run to the next except for the concentration of one reactant.
What unit is R in in Arrhenius equation?
J/(K*mol)
Which of the following statements is false regarding the equilibrium constant, K c? K c for the reverse reaction is the negative of K c for the forward reaction. The numerical value of K c depends on the form of the balanced equation. K c for a reaction at a particular temperature always has the same value. When quoting K c it is customary to omit units.
K c for the reverse reaction is the negative of K c for the forward reaction.
What temperature unit is Arrhenius equation in?
Kelvins
The compound BF3 can be described as a(n) ________.
Lewis acid
If the units for rate are M s-1, what are the units for the rate constant, k, for a zeroth-order reaction?
M s-1
Which of the following does not affect the rate of a bimolecular reaction?
None. Concentrations of reactants, presence of a catalyst, temperature all affect the rate
Spontaneous reactions (∆G < 0) ______ fast.
Not necessarily fast
For the reaction CaCO3(s)⇌CaO(s)+CO2(g)CaCO3(�)⇌CaO(�)+CO2(�) the equilibrium expression is Kp = ________.
PCO2
As a rule, which of the following phases are not included in the equilibrium constant expression? I. pure liquids II. pure solids III. aqueous solutions IV. gases
Pure liquids & pure solids
Which general rate law below corresponds to an elementary bimolecular reaction?
Rate = k[A][B]
What is the rate law for the elementary reaction shown below? 2 HI → H2 + I2
Rate = k[HI]2
The exothermic reaction 2A(g) + B(s) ⇌ C(g) + H2O(g) is at equilibrium. Predict which one of the following actions will cause [C] to increase.
Remove half of the product H2O.
What integrated rate law correspond with Rate = k[A][B]
Second order
Which one of the following statements does not describe the equilibrium state? The concentration of the reactants is always equal to the concentration of the products. The rate of the forward reaction is equal to the rate of the reverse reaction. Equilibrium is dynamic and there is no net conversion to reactants and products. The concentration of the reactants and products reach a constant level.
The concentration of the reactants is always equal to the concentration of the products.
Know the units of the rate constant k for first-order and second-order reactions.
Units of first - 1/s Units of second - 1/(m*s)
For the zeroth-order reaction: C → products, -Δ[C]/Δt = k, which of the following graphs would be expected to give a straight line?
[C] vs. t In a zeroth-order reaction where the rate of the reaction is independent of the concentration of the reactant
What is the minimum energy barrier that must be overcome for a chemical reaction to occur?
activation energy
For a homogeneous equilibrium of gases, which of the following changes in reaction conditions will not alter the equilibrium concentrations? increasing the temperature additional of reactants decreasing the pressure addition of an inert gas to the reaction mixture
addition of an inert gas to the reaction mixture
The elementary reaction: 2 HCl → H2 + Cl2, is an example of a ________ reaction.
bimolecular
A catalyst increases the overall rate of reaction by lowering the activation energy, Ea, for
both the forward reaction and the reverse reaction.
For the reaction shown below, what is the order of reaction with respect to ClO−ClO−ClO−2(aq)+4 Br−(aq)+4 H+(aq)→Cl−(aq)+2 Br2(aq)+2 H2O(l)
can't tell from the information provided the order cannot be determined using the balanced reaction only. It has to be determined experimentally
form of a differential rate law ________ predicted from the stoichiometry of the reaction
cannot
Instantaneous rate
change in the rate at a particular instant. It is the same as the change in derivative value at a specific point.
What factor affects the rate of a chemical reaction?
collision frequency, fraction of collisions with sufficient energy, orientation of molecules
elementary step is a _________ mechanism
concerted - only one transition state
heterogeneous catalyst
different phase than the reactants
Chemical equilibrium, the rates of the forward and reverse reactions are ______.
equal
A catalyst increases the rate of a chemical reaction by providing a lower-energy mechanism for the reaction. When this occurs, which one of the following is not affected?
equilibrium constant
how does Steric factor affect reaction rate?
fraction of collisions with right orientation. The ratio between the experimental value of the rate constant and the one predicted by collision theory. This steric factor is usually always less than 1 because the steric requirement lowers the probability of the reaction occurring. If the steric factor is equal to 1, that means both atoms can collide with each other in any orientation and produce a reaction.
Homogeneous catalyst
in the same phases as reactants
For a reaction that follows the general rate law, Rate = k[A][B]2, what will happen to the rate of reaction if the concentration of B is increased by a factor of 5.00? The rate will
increase by a factor of 25.00.
For a reaction that follows the general rate law, Rate = k[A][B]2, what will happen to the rate of reaction if the concentration of A is increased by a factor of 5.00? The rate will
increase by a factor of 5.00.
What alters the composition of an equilibrium mixture?
increase the pressure, increase the volume, and increase the temperature
Which of the following will result in an increase in the amount of NH4Cl? NH4Cl (s) ↔ NH3 (g) + HCl (g)
increasing the amount of NH3 (g)
The first-order decomposition of hydrogen peroxide occurs according to the equation 2 H2O2(aq) → 2 H2O(l) + O2(g) Using data from a concentration-time study of this reaction, which plot will produce a straight line?
ln[H2O2] versus time
A catalyst increases the rate of a reaction by providing a different reaction pathway that
lowers only the activation energy.
Elementary step
one step in a series of simple reactions that show the progress of a reaction at the molecular level.
Activation energy (transition state)
potential energy of reactants
how does collision frequency affect reaction rate?
proportional to the number of collisions over time. increasing the concentration of either reactant increases the number of collisions, and therefore increases the number of successful collisions and the reaction rate
Reaction mechanisms
sequence of elementary steps by which a chemical reaction occurs.
On an integrated rate law graph, what does the slope equal?
slope = -k
Rate-determining step
slowest step within the chemical reaction
Chemical equilibrium
state in which the rate of the forward reaction equals the rate of the backwards reaction.
Catalyst
substance that increase the rate of a chemical reaction without itself undergoing any permanent
The elementary reaction representing the formation of ozone: O2(g) + O(g) + M(g) → O3(g) + M*(g) is an example of a ________ reaction.
termolecular
Unimolecular and bimolecular elementary reactions are common, but __________ are very rare
termolecular ones
Order of reaction
the power dependence of rate on the concentration of all reactants.
Reaction rate & unit
the speed at which a chemical reaction proceeds. Change in concentration/change in time. Unit m/s
how does collision energy affect reaction rate?
the speed at which reactant molecules must be moving to get over transition. More collisions mean a faster reaction rate, assuming the energy of the collisions is adequate
Total reaction order
the sum of orders for each reactant
What is the overall reaction order for the reaction that has the rate law: Rate=k[Br2][NO2]2
third order
Transition state (activated complex)
where some bonds are being formed and others broken has higher potential energy than either reactants or products
The decomposition of ammonia to nitrogen and hydrogen on a tungsten filament at 800°C is independent of the concentration of ammonia at high pressures of ammonia. What is the order of the reaction with respect to ammonia?
zero
