CHM142 Exam 2
Which types of intermolecular forces contribute to attractive interactions between difluoromethane (CH2F2) molecules? A. hydrogen bonding B. dispersion C. dipole-dipole D. dipole-induced dipole
B, C and D
Consider three solutions characterized by [H+], [OH-] and pOH: A: [H+] = 3.2 x 10-7 M B: [OH-] = 2.2 x 10-8 M C: pOH = 7.41 Arrange them in order of increasing acidity (from the least to the most acidic).
C, A , B
what state is chemical equilibrium in? Dynamic or stationary?
Dynamic
The dependence of rate constants on temperature is given by the Arrhenius equation k = Ae-Ea/RT . Under what conditions will k have the largest value?
Ea = 65 kJ/mol; T = 400 ºC
Which of the following arrangements of two diatomic molecules exhibits hydrogen bonding? F-H . . . H-F H-F . . . H-F H-H . . . F-H H-H . . . H-F H-F . . . F-H
H-F . . . H-F
The rate law for a decomposition of H2O2 in an aqueous solution that contains iodide ions, I-(aq), is Rate = k[H2O2][I-]. Which of the following elementary reactions could be the rate-determining step? H2O2(aq) + I-(aq) → H2O(l) + OI-(aq) H2O2(aq) → H2O(l) + O(g) H2O2(aq) + H+(aq) + I-(aq) → H2O(l) + HOI(aq) 2H2O2(aq) → 2H2O(l) + O2(g) H2O2(aq) + 2I-(aq) → 2OH-(aq) + I2(s)
H2O2(aq) + I-(aq) → H2O(l) + OI-(aq)
Which of the following is the strongest acid? HNO2 (Ka = 4.5 x 10-4) HN3 (Ka = 1.9 x 10-5) HCN (Ka = 4.9 x 10-10) HClO2 (Ka = 1.1 x 10-2) HF (Ka = 6.8 x 10-4)
HClO2 (Ka = 1.1 x 10^-2)
Which is the correct equilibrium constant Kp for the following reaction? Na2CO3(s) + SO2(g) + (1/2)O2(g) ⇌ Na2SO4(s) + CO2(g)
Kp = PCO2 / [ PSO2 · (PO2)^1/2 ]
if a system at equilibrium is disturbed, the system will move to restore equilibrium
Le Chateliers Principle
For which of the following reactions a decrease of pressure at constant temperature will shift the equilibrium to the left? 2H2S(g) + CH4(g) → 4H2(g) + CS2(g) 2NO2(g) → 2NO(g) + O2(g) 4NH3(g) + 3O2(g) → 2N2(g) + 6H2O(g) N2(g) + 3H2(g) → 2NH3(g) 2NOCl(g) → 2NO(g) + Cl2(g)
N2(g) + 3H2(g) → 2NH3(g)
The rate law for the reaction 2NO(g) + Cl2(g) → 2NOCl(g) is: Rate = k [NO][Cl2]. Which of the following is the rate-determining step for this reaction? NOCl2(g) + NO(g) → 2NOCl(g) NOCl2(g) → NO(g) + Cl2(g) NO(g) + NO(g) → N2O2(g) 2NO(g) + Cl2(g) → 2NOCl(g) NO(g) + Cl2(g) → NOCl2(g)
NO(g) + Cl2(g) → NOCl2(g)
Which statement is true about the following reaction? 2NO(g) + O2(g) → 2NO2(g) The reaction occurs in a single step. The rate-determining step is termolecular. None of the other statements can be determined from the information given. The reaction is third order overall. The rate law is: Rate = k[NO]2[O2].
None of the other statements can be determined from the information given.
The mechanism of the reaction between gaseous NO and Br2 is thought to be NO(g) + Br2(g) ⇌ NOBr2(g) (rapid equilibrium) NOBr2(g) + NO(g) → 2NOBr(g) (slow) What rate law is predicted by the mechanism when the rate-determining step approximation is used?
Rate = k[NO]2[Br2]
The reaction rates of many spontaneous reactions are actually very slow. Which of the following is the best explanation for this observation? - Such reactions are endothermic. - Such reactions have extremely small equilibrium constants. - Such reactions are exothermic. - Such reactions have extremely large equilibrium constants. - Such reactions have large activation energies.
Such reactions have large activation energies
At 927.0 ºC, the reaction CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g) has an equilibrium constant Kc = 3.92. A mixture was prepared in which, initially, the following concentrations were present [CO] = 0.010 M, [H2] = 0.10 M, [CH4] = 0.010 M, [H2O] = 0.010 M. Which one of the following statements is true? The system is at equilibrium, no change. You Answered - The concentration of CO will fall as the system approaches equilibrium. - The concentration of CO and CH4 will fall as the system approaches equilibrium. - The concentrations of CH4 and H2O will fall as the system approaches equilibrium. - The concentration of CH4 and H2O will increase as the system approaches equilibrium.
The concentrations of CH4 and H2O will fall as the system approaches equilibrium
When temperature was raised and pressure was kept constant the amount of products in the equilibrium mixture decreased. Which of the following is the best explanation of why that happened? The reaction quotient decreased so the equilibrium shifted to the left The value of the equilibrium constant increased so the amount of products in the equilibrium mixture decreased. The value of the equilibrium constant decreased so the amount of products in the equilibrium mixture decreased. Heat was absorbed by the reaction so the equilibrium shifted to the left The reaction quotient increased so the equilibrium shifted to the left
The value of the equilibrium constant decreased so the amount of products in the equilibrium mixture decreased.
Which of the following plots is linear for a second-order reaction? ln[A] versus t [A]-1 versus t [A] versus t [A] versus t-1 [A]-1 versus t-1
[A]-1 versus t
large Ka value indicates
a strong acid
Which of the following cannot act a Brønsted-Lowry acid? HPO42- (H3C)3N HF NH4+ HCOOH
(H3C)3N
A reaction has the activation energies of 34.5 and 52.7 kJ/mol for the forward and reverse steps, respectively. What is the energy change (∆E = Eproducts - Ereactants) for this reaction?
-18.2 kJ/mol
The equilibrium constant Kc for the reaction H2(g) + I2(g) ⇌ 2HI(g) is 50.2 at 445 ºC. Find the equilibrium concentration of HI knowing that the initial concentrations of all the species were equal to 0.0200 M.
0.0468 M
The rate constant for the reaction 2N2O5(g) → 4NO2(g) + O2(g) is equal to 3.41 x 10-5 s-1 at 30 ºC. If the initial concentration of N2O5 is 0.446 M what concentration of NO2 will be observed after 175 minutes? Assume that initially no NO2 was present in the reaction vessel.
0.268 M
The reaction 2N2O(g) → 2N2(g) + O2(g) is a first-order reaction. If the initial concentration N2O is equal to 0.372 M and the rate constant is 7.54 x 10-3 M s-1, what will the concentration be after 11.5 s?
0.341 M
The rate constant for a reaction involving reactant A is 3.14 x 10-4 M s-1. If the initial concentration of A is 0.626 M, what will be the concentration of A after 195 seconds?
0.565 M
What is the molarity of a solution of Ba(OH)2 that has the pH=12.30?
1.0 x 10^-2 M
Consider the following reaction 4NH3(g) + 7O2(g) → 4NO2(g) + 6H2O(g) If O2(g) is being consumed at a rate of 8.33 x 10-5 M s-1, what is the rate of the reaction?
1.19 x 10-5 M s-1
The activation energy for the reaction 2HI(g) → H2(g) + I2(g) is 184.0 kJ/mol. If the rate constant for this reaction is 2.70 x 10-4 M-1 s-1 at 327.0 ºC what would be the rate constant at 352.0 ºC?
1.2 x 10-3 M^-1 s^-1
The initial partial pressures of NO, N2O and NO2 in the reaction vessel were 0.977, 0.211 and 0.179 atm, respectively. The following reaction was allowed to come to equilibrium 3NO(g) ⇌ N2O(g) + NO2(g) and the equilibrium partial pressure of NO was found to be 0.059 atm. Find the value of Kp for this reaction.
1.2 x 10^3
Consider the following first-order reaction: 2N2O(g) → 2N2(g) + O2(g) If the concentration of N2O drops from 3.76 x 10-3 M to 2.28 x 10-3 M in 327 s, what will the concentration of N2O be after 654 s?
1.38 x 10-3 M
The value of Kc for the following reaction is 78.0 SO2(g) + NO2(g) ⇌ SO3(g) + NO(g) What is the value of Kc for the reaction 2SO3(g) + 2NO(g) ⇌ 2SO2(g) + 2NO2(g)
1.64 x 10^-4
What is the pH of a 1.7 x 10-3 M solution of NaOH at 50.0 ºC? (At 50.0 ºC, Kw = 5.47 x 10-14)
10.49
What is the pH of a solution obtained by dissolving 1.5 x 10-3 mol of Ba(OH)2 in 200.0 mL in water?
12.18
The half-life for the first-order reaction A(g) → B(g) + C(g) is 125 s at an initial concentration of A of 0.325 M. The concentration of A will be reduced to 37.0% of its original concentration after
179 s
The half-life for the first-order reaction A(g) → B(g) + C(g) is 115 s at an initial concentration of A of 0.286 M. How long will it take for 69.0% of A to react?
194 s
Consider the two gaseous equilibria and the associated KP values 2SO2(g) + O2(g) → 2SO3(g) KP = 6.79 x 1024 SO2(g) + NO2(g) → SO3(g) + NO(g) KP = 1.75 x 106 What is the value of KP for the following equilibrium 2NO(g) + O2(g) → 2NO2(g)
2.23 x 10^12
Initially, a 200.0 L vessel contained 2.864 mol of SO2, 3.352 mol of O2 and 1.556 mol of SO3. The following reaction was allowed to come to equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g) and the equilibrium mixture was found to contain 2.672 mol of O2. Find the value of Kc for this reaction.
281
The value of Kc for the following reaction is 3.57 at 900.0 ºC. CH4(g) + 2H2S(g) ⇌ CS2(g) + 4H2(g) What is the value of Kp at this temperature?
3.3 x 10^4
Consider the two gaseous equilibria 2SO2(g) + O2(g) ⇌ 2SO3(g) Kc = 4.4 x 106 SO2(g) + NO2(g) ⇌ SO3(g) + NO(g) Kc = 7.8 x 101 What is the equilibrium constant for the following reaction? NO2(g) ⇌ NO(g) + (1/2)O2(g)
3.7 x 10^-2
The decomposition of NO2 2NO2(g) → 2NO(g) + O2(g) is second-order in NO2. Given that the concentration of NO2 decreases from 5.46 x 10-2 M to 3.74 x 10-2 M in 21.3 s find the half-life of the reaction when [NO2]0 = 5.46 x 10-2 M.
46.3 s
At 40 ºC Kw is equal to 2.92 x 10-14. At that temperature a solution is neutral if it has a pH of
6.77
For the reaction N2O4(g) → 2NO2(g) measurement of the compositions of equilibrium mixtures gave Kp = 0.144 at 25.00 ºC and Kp = 0.321 at 35.00 ºC. Find ∆Hº for this reaction.
61.2 kJ/mol
The rate constant for the reaction 2NO2(g) → 2NO(g) + O2(g) is 0.17 M-1 s-1. What is the half-life for this reaction when the initial concentration of NO2 is 0.0640 M?
92 s
substance with H in its formula that dissociates to yield H3O+.
acid
Which of the following changes would cause the equilibrium Fe2O3(s) + 3CO(g) ⇌ 2Fe(s) + 3CO2(g) ∆Hº = -24.74 kJ/mol to shift to the right? adding more Fe2O3 adding more CO2 adding more CO adding more Fe adding a catalyst
adding more CO
if Q = K
at equilibrium
substance with OH in its formula that dissociates to yield OH-.
base
a substance that reacts in the first step and is still around at the end
catalyst
that particles must collide in order to react.
collision theory
Addition of H2 to the reaction vessel in which N2 reacts with H2 to form NH3 N2(g) + 3H2(g) → 2NH3(g) while keeping the temperature and volume constant will
decrease the concentration of N2 but will not affect Kp for the reaction.
pressure and equilibrium
favors the side with fewer molecules
ln [A]t = -kt + ln[A]0
first order
t0.5 = ln2/k
half life first order
t0.5 = 1/k[A]0
half life second order
t0.5 = [A]0/2k
half life zero order
Consider the following reaction at equilibrium 2CO2(g) ⇌ 2CO(g) + O2(g) ∆Hº = 566 kJ/mol The amount of CO(g) produced by this reaction can be maximized by carrying out the reaction at
high temperature and low pressure.
higher T and larger K mean...
increase reaction rate
The rate law of the overall reaction NO2(g) + CO(g) → NO(g) + CO2(g) is Rate = k[NO2]2 . Which of the following will not increase the rate of the reaction? All other answers are correct. increasing the concentration of CO running the reaction at higher temperature adding a catalyst to the reaction mixture increasing the concentration of NO2
increasing the concentration of CO
formed in the first step but disappears
intermediate
smaller Ea means
larger K and increased rate
what does a large k value indicate?
leaves little reactants, so favors products
Convert the following exponential function into a logarithmic form and choose the plot that is linear. z = Ae ^ (Bt^2) (z and t are variables, and A and B are constants)
ln z vs. t2
a catalyst provides an alternate reaction path that has a ____ total activation energy than the uncatalyzed reaction
lower
Which of the following relationships is true for pure water at any temperature? pKw = 14.0 pH = pOH pH = 7.0 [H3O+] = [OH-] = 1.0 x 10-7 M pOH = 14.0 - pH
pH = pOH
if Q is smaller than K...
reactants decreased and products increase - moves to the right
if Q is larger than K...
reactants increase and products decrease - moves to the left
1/[A]t = kt + 1/[A]0
second order
if a product is added to the equation...
shift to the left
if a reactant is removed from the equation
shift to the left
if a product is removed from the equation...
shift to the right
if a reactant is added to the reaction...
shift to the right
Convert the following exponential function into a logarithimic form and determine the slope and the y-intercept of the linear plot. z = Ae ^ (Bt^2) (z and t are variables, and A and B are constants)
slope: -B; y-intercept: ln A
acid dissociates completely into ions in water
strong acid
how is the reaction quotient different from the equilibrium constant?
the reaction quotient uses the initial concentrations of the reactants and products whilst the equilibrium constant uses the equilibrium concentrations
a decrease in temperature will shift the reaction...
to the left
an increase in temperature will shift the reaction...
to the right
dissociates slightly to form ions in water
weak acid
a smaller Ka value indicated
weaker acid
what does a small K value indicate?
yields little product, so favors reactants
[A]t-[A]0 = -kt
zero order
Choose the reaction that at equilibrium is described by the following equilibrium constant expression Kc = [HCl] / ( [H2]½ [Cl2]½ ) H2(g) + Cl2(g) ⇌ 2HCl(g) ¼H2(g) + ¼Cl2(g) ⇌ ½HCl(g) HCl(g) ⇌ H2(g) + Cl2(g) HCl(g) ⇌ ½H2(g) + ½Cl2(g) ½H2(g) + ½Cl2(g) ⇌ HCl(g)
½H2(g) + ½Cl2(g) ⇌ HCl(g)
