Chapter 14 Practice Test Flashcards
Hydrofluoric acid is a weak acid with an equilibrium constant (at 25°C) of Ka = 7.2 x 10^-4 . What is the pH of a 1.00 M solution of this acid?
1.57
Using the graph below, calculate the instantaneous reaction rate for the formation of NO at 100.0 s, and tell whether the instantaneous rate at 100.0 s is faster or slower than the instantaneous rate at 50.0 s.
1.34 × 10^−4 M / s, slower at 100s
Mercury(II) chloride (HgCl2 ) reacts with oxalate ions (C2O42− ) according to the following equation.
2HgCl2(aq) + C2O42− (aq) → 2Cl − (aq) + 2CO2(g) + Hg2Cl2(s)
If Δ[CO2 ] / Δt = 5.2 × 10−7 M / s,
what is the value of Δ[C2O42− ] / Δt at the
same instant?
−2.6 × 10^−7 M / s
Chlorine gas(Cl2 ) reacts with fluorine gas (F2 ) according to the following equation.
Cl2(g) + 3F2(g) → 2ClF3(g)
Suppose you combine one mole of Cl2 with three moles of F2, and then made a graph of the concentration of the reactants and the products versus time. Which of the following statements would be true of the graph at time = t ?
The slope of the curve for ClF3 will equal twice the rate of the reaction.
Suppose you are studying the following reaction.
2A + B → 2C + D
You gather the following initial rate data for the reaction:
What will be the rate of formation of C when [A] is 0.040 M and [B] is 0.040 M?
0.084 M / s
Suppose you are studying the following reaction:
2A + 2B → C + 2D
You find that when you double the concentration of A while keeping the concentration of B fixed, the rate of the reaction increases by a factor of 2. What conclusion can you draw about the rate law of this reaction?
The rate law is first order in [A].
The following data are gathered for the radioactive decay of flourine-20
Time 0.0 2.0 4.0 6.0
Concentration 0.24 0.21 0.18 0.16
If the decay of 20F is a first-order reaction, which of the following is the best estimate of its half-life
10 s
Consider the following first-order reaction.
A → B + C
The half-life of this reaction is 6.40 hours. Suppose you define the third-life (t1/3 ) of the reaction as the time at which one-third of the original amount of A remains. What is t1/3 for this reaction?
10 hours
The reaction 2D -> 2E + F is second order in [D] and second order overall. The rate constant of this reaction at a particular temperature is 4.88 * 10^-3 M^-1s^-1. If the initial concentration of D is 1.95 M, what will be the rate of reaction a t = 900 s?
5.69 × 10^−5 M / s
Suppose you are studying the following pair of reactions.
A → D + E
2B → D + E
The first reaction is first order in [A] and first order overall with a rate constant of 0.30 s−1. The second reaction is second order in [B] and second order overall with a rate constant of 0.30 M −1s−1. If [A]0 = [B]0 = 0.10 M, how much longer will the half-life of the second reaction be than the half-life of the first reaction at t = 0?
14 s
Calculate the concentration of a sucrose solution that had an original concentration of 5.00 g / L after 6.00 hours and 20.0 minutes. The rate constant for this reaction at 300 K is 4.10 × 10−2 hr−1.
3.86 g / L
Compound XY decomposes to form X and Y in a reaction that is first order with respect to XY and first order overall. The half-life for the reaction is 15.4s. What is the specific rate constant of this reaction as 25 degrees C?
XY -> X + Y
4.50 × 10−2 s−1
If the temperature of the reactants is increased by 30° C, and all other factors remain constant, how will this affect the reaction rate?
It will increase 8 fold
Consider the relationship among activation energy, temperature, and the specific rate constant of a reaction:
k = A
If Ea decreases, the effect will be all of the following except:
The reaction slows down.
In the formula for the rate of a chemical reaction, which expression changes with temperature?
rate = k[A]m[B]n
k
Which of the following is the Arrhenius equation for reaction rate?
k = Ae ^−Ea/RT
Which of the following is not a constant in the Arrhenius equation?
T
Given the following information, find the activation energy for the decomposition of acetaldehyde.
k1 = 1.05 × 10−3 M −1/2s−1 at 759 K k2 = 2.14 × 10−2 M −1/2s−1 at 836 K
2.06 × 10^5 J / mol
The molecularity of an elementary step of a reaction refers to:
the number of molecules that collide in the elementary step of a reaction.
What is the molecularity of each step in the following reaction sequence? Step 1a: Cl2 → 2Cl
Step 1b: 2Cl → Cl2
Step 2: Cl + CHCl3 → HCl + CCl3
Step 3: Cl + CCl3 → CCl3
Step 1a: Unimolecular, Step 1b: Bimolecular, Step 2: Bimolecular, Step 3: Bimolecular
Which of the following is the rate law expression for the following chemical reaction? This reaction occurs in one step and has no reaction intermediates.
2 NO(g) + O2(g) → 2 NO2(g)
k[ NO]2 [O2 ]
In the formula for the rate of a chemical reaction, which expression changes with temperature?
rate = k[A]m [B]n
k
In a proposed two-step mechanism for the reaction, CO(g) + NO2(g) → CO2(g) + NO(g), the second, fast, step is NO3 + CO → NO2 + CO2. What is the expected rate law of this reaction?
rate of reaction = k[ NO2 ]2
The rate law for the reaction, 2NO(g) + O2(g) → 2NO2(g), is found to be: rate of reaction = k [ NO]2 [O2 ]2.
The first, fast step is 2NO(g) ↔ N2O2(g).
What is the value of Δ[ N2O2 ] / Δt ?
0
A catalyst has which of the following properties?
A catalyst increases the rate of a reaction.
