Chem 2 Test 2

For the reaction 2AsH3 (g) → As2 (g) + 3H2 (g), the reaction rate can be given by ______ .

+∆[As2]/∆t

The reaction below is exothermic: 2SO2 (g) + O2 (g) ↔ 2SO3 (g) Le Châtelier's Principle predicts that _______ will result in an increase in the number of moles of SO3 (g) in the reaction container. increasing the volume of the container decreasing the pressure increasing the temperature decreasing the temperature removing some oxygen

...

Which of the following expressions is the correct equilibrium-constant expression for the reaction below? HF (aq) + H2O (l) ↔ H3O+ (aq) + F- (aq) [H3O+][F-] / [HF][H2O] [HF][H2O] / [H3O+][F-] [H3O+][F-] / [HF] 1 / [HF] [F-]/[HF]

...

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) → B(g). The following data are obtained for [A] as the reaction proceeds: Time (s) 0.00 10.0 20.0 30.0 40.0 Moles of A 0.124 0.110 0.088 0.073 0.054 How many moles of B are present at 30 s?

0.051 mol

The combustion of ethylene proceeds by the reaction C2 H4(g) + 3O2 (g) → 2CO2 (g) + 2H2O(g) When the rate of disappearance of O2 is 0.18 M s−1, the rate of disappearance of C2 H4 is _______ M s−1. 0.36 0.27 0.060 0.12 0.54

0.060

Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution: HC2H3O2 (aq) ↔ C2H3O2 - (aq) + H+ (aq) At equilibrium at 25 °C a 0.100 M solution of acetic acid has the following concentrations: [HC2H3O2] = 0.0990 M, [C2H3O2 -] = 1.33 ⋅ 10-3 M, and [H+] = 1.33 ⋅ 10-3 M. The equilibrium constant, Keq, for the ionization of acetic acid at 25°C is . 1.75 ⋅ 10-7 1.79 ⋅ 10-5 5.71 ⋅ 106 0.100 5.71 ⋅ 104

1.79 ⋅10-5

The equilibrium constant for reaction 1 is K. The equilibrium constant for reaction 2 is: (1) SO2 (g) + (1/2) O2 (g) ⇌ SO3 (g) (2) 2SO3 (g) ⇌ 2SO2 (g) + O2 (g) 2K K2 -K2 1/K2 1/2K

1/K2

The data in the table below were obtained for the reaction: 2ClO2 (aq) + 2OH- (aq) → ClO3 - (aq) + ClO2 - (aq) + H2O (1) What is the order of the reaction with respect to ClO2? Experiment Number [ClO2] (M) [OH-] (M) Initial Rate (M/s) 1 0.060 0.030 0.0248 2 0.020 0.030 0.00276 3 0.020 0.090 0.00828

2

Of the following equilibria, only _____ will shift to the left in response to a decrease in volume. H2 (g) + Cl2 (g) ↔ 2 HCl (g) 4 Fe (s) + 3 O2 (g) ↔ 2 Fe2O3 (s) 2 SO3 (g) ↔ 2 SO2 (g) + O2 (g) 2HI (g) ↔ H2 (g) + I2 (g) N2 (g) + 3H2 (g) ↔ 2 NH3 (g)

2 SO3 (g) ↔ 2 SO2 (g) + O2 (g)

Consider the following chemical reaction: CO (g) + 2H2(g) ↔ CH3OH(g) At equilibrium in a particular experiment, the concentrations of CO and H2 were 0.15 M and 0.36 M, respectively. What is the equilibrium concentration of CH3OH? The value of Keq for this reaction is 14.5 at the temperature of the experiment. 3.72 ⋅ 10-3 14.5 7.61 ⋅ 10-3 1.34 ⋅ 10-3 2.82 ⋅ 10-1

2.82 ⋅ 10-1

The diagram shown here represents the equilibrium state for the reaction A2(g) + 2B(g) ⇌ 2AB(g). Assuming the volume is 2 L, calculate the equilibrium constant Kc for the reaction. If the volume of the equilibrium mixture is decreased, will the number of AB molecules increase or decrease? The number of AB molecules decrease. The number of AB molecules increase

4, The number of AB molecules increase.

For the reaction: CH3OH(g) ⇌ CO(g) + 2H2(g), with the equilibrium concentrations for [CH3OH] = 0.20 M, [CO] = 0.44 M, and [H2] = 2.7 M, determine the gas phase equilibrium constant (K p) at 400 0C? 16 4.9 x 106 0.49 x 103 4.9 x 104

4.9 x 104

Nitrogen dioxide decomposes to nitric oxide and oxygen via the reaction: 2NO2 → 2NO + O2 In a particular experiment at 300 ∘ C, [NO2 ] drops from 0.0269 to 0.00896 M in 243 s . The rate of disappearance of NO2 for this period is ________ M/s. 1.48×10−4 3.69×10−5 −1.48×10−4 7.38×10−5 1.35×104

7.38x10-5

A second-order reaction has a half-life of 18 s when the initial concentration of reactant is 0.71 M. The rate constant for this reaction is ______ M-1s-1.

7.8 ⋅ 10-2

The half-life of a first-order reaction is 13 min. If the initial concentration of reactant is 0.085 M, it takes _______ min for it to decrease to 0.055 M. 8.2 8.4 3.6 0.048 11

8.2

Under constant conditions, the half-life of a first-order reaction _________. does not depend on the initial reactant concentration is constant is the time necessary for the reactant concentration to drop to half its original value can be calculated from the reaction rate constant All of the above are correct.

All of the above are correct.

As a reaction proceeds, does the instantaneous reaction rate increase or decrease? As a reaction proceeds, the instantaneous reaction rate decreases. As a reaction proceeds, the instantaneous reaction rate increases.

As a reaction proceeds, the instantaneous reaction rate decreases.

As the temperature increases, does the reaction rate increase or decrease? As temperature increases, reaction rate increases. As temperature increases, reaction rate decreases.

As temperature increases, reaction rate increases.

A certain reaction A ⇌ B reaches equilibrium. Which of the following statements about the equilibrium is or are true? At equilibrium, the concentrations of A and B in the reaction mixture must be equal. At equilibrium, the processes A ➔ B and B ➔ A have the same reaction rates. At equilibrium, molecules of A are no longer converted into molecules of B.

At equilibrium, the processes A ➔ B and B ➔ A have the same reaction rates.

What is the molecularity of the elementary reaction? NO(g) + Cl2 (g) ⟶ NOCl(g) + Cl(g) Unimolecular Bimolecular Termolecular No such reaction will take place.

Bimolecular

Adding heat to an exothermic reaction will have what effect? Reactants ↔ products + heat Causes the equilibrium to shift to the right, in the direction of making more reactants, and K increases. No effect and K doesn't change. Causes the equilibrium to shift to the left, in favor of making more reactants, and K decreases. Causes the equilibrium to shift to the right, in the direction of making more products, and K increases.

Causes the equilibrium to shift to the left, in favor of making more reactants, and K decreases

Rates of reaction can be positive or negative. True False

False

Units of the rate constant of a reaction are independent of the overall reaction order. True False

False

If the rate = [P]2[G][O] then the overall reaction order is what? Fourth order overall Third order overall First order overall Second order overall

Fourth order overall

For C2H2(g) + 2 H2(g) ⇌ C2H6(g). Which of the following is the correct relationship between K c and K p for this equilibrium? Kp = Kc / (RT)2 Kp = Kc(RT)2 Kp = Kc Kp = Kc / (RT) Kp = Kc(RT)

K p = K c / (RT)2

The rate law of a reaction is rate = k[D][X]. The units of the rate constant are______ . L2 mol-2s-1 mol L-1s-1 L mol-1s-1 mol2 L-2s-1 mol L-1s-2

L mol-1s-1

Of the units below, ________ are appropriate for a third-order reaction rate constant. Ms−1 M-1s-1 s-1 M-2s-1

M-2s-1

What is the unit usually used to express the rates of reactions occurring in solution? kg/min L/s M/s kg/s

M/s

Of the following equilibria, only _____ will shift to the right in response to a decrease in volume. H2 (g) + Cl2 (g) ↔ 2 HCl (g) N2 (g) + 3H2 (g) ↔ 2NH3 (g) 2HI (g) ↔ H2 (g) + I2 (g) 2 SO3 (g) ↔ 2 SO2 (g) + O2 (g) 2 Fe2O3 (s) ↔ 4 Fe (s) + 3O2 (g)

N2 (g) + 3H2 (g) ↔ 2NH3 (g)

In which of the following reactions would increasing pressure at constant temperature not change the concentrations of reactants and products, based on Le Châtelier's principle? 2N2 (g) + O2 (g) ↔ 2N2O (g) N2 (g) + 3H2 (g) ↔ 2NH3 (g) N2 (g) + 2O2 (g) ↔ 2NO2 (g) N2 (g) + O2 (g) ↔ 2NO (g) N2O4 (g) ↔ 2NO2 (g)

N2 (g) + O2 (g) ↔ 2NO (g)

Is the rate of disappearance of reactants always the same as the rate of appearance of products? No Yes

No

Does the rate constant have the same units as the rate? Yes, the units for both the rate constant and the rate depend on the specific rate law. No, the units for the rate constant depend on the specific rate law, while the rate has units of M/s. Yes, the rate constant and the rate both have units of M/s. No, the rate constant has units of M/s, while the units for the rate depend on the specific rate law.

No, the units for the rate constant depend on the specific rate law, while the rate has units of M/s.

Which substance in the reaction below either appears or disappears the fastest? 4NH3 + 7O2 →→ 4NO2 + 6H2O O2 NO2 H2O NH3 The rates of appearance/disappearance are the same for all of these.

O2

What factors determine whether a collision between two molecules will lead to a chemical reaction? Concentration of the molecules Energy of the collision Masses of the colliding molecules Orientation of the molecules Atmospheric pressure

Orientation of the molecules,Energy of the collision

Which of the following statements is true? Q does not depend on the concentrations or partial pressures of reaction components. Q does not change with temperature. Keq does not change with temperature, whereas Q is temperature dependent. Q is the same as Keq when a reaction is at equilibrium. K does not depend on the concentrations or partial pressures of reaction components.

Q is the same as Keq when a reaction is at equilibrium.

What is the Le Châtelier's Principle ? States: that the position of the equilibrium will shift in a direction to increase any change imposed on a system. States: that if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction to reduce that change. States: that no change can be imposed on chemical reaction at equilibrium. States: that if a change is imposed on a system at equilibrium, the position of the equilibrium will not shift in a direction to reduce that change.

States: that if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction to reduce that change.

Does the equilibrium 2 NO (g) + O2 (g) ⇋ 2 NO2 (g) shift to the right (more products) or left (more reactants) if NO is removed? The equilibrium shifts to the right. The equilibrium shifts to the left. There will be no changes.

The equilibrium shifts to the left.

Does the equilibrium 2 NO (g) + O2 (g) ⇋ 2 NO2 (g) shift to the right (more products) or left (more reactants) if O2 is added to the system? The equilibrium shifts to the right. The equilibrium shifts to the left. There will be no changes.

The equilibrium shifts to the right.

In a chemical reaction dynamic equilibrium occurs when? The rate of the reverse reaction exceeds the rate of the forward reaction. The rate of the forward reaction equals the rate of the reverse reaction. The rate of the forward reaction exceeds the rate of the reverse reaction. When the rates of forward and reverse reactions are irreversible.

The rate of the forward reaction equals the rate of the reverse reaction.

In a reaction involving reactants in the gas state, how does increasing the partial pressures of the gases affect the reaction rate? The rate will increase The rate will decrease The rate will not change

The rate will increase

Considering the reaction below at equilibrium, which of the following statements is correct? N2O4 (g) ⇄ 2NO2 (g) The ratio of [NO2]2/[N2O4] is not changing. The concentration of N2O4 is equal to the concentration of NO2. N2O4 can no longer react to form NO2. NO2 is being formed more quickly than N2O4.

The ratio of [NO2]2/[N2O4] is not changing.

If the equilibrium constant (K) is less than 1 then what occurs? The products predominate. Equilibrium is not achieved. Neither products or reactants predominate. The reactants predominate.

The reactants predominate.

How is the reaction quotient used to determine whether a system is at equilibrium? At equilibrium, the reaction quotient is undefined. The reaction quotient must be satisfied for equilibrium to be achieved. The reaction is at equilibrium when Q = Keq. The reaction is at equilibrium when Q < Keq. The reaction is at equilibrium when Q > Keq.

The reaction is at equilibrium when Q = Keq.

The rate law for a reaction is: rate = k[A][B]2 Which one of the following statements is false? If [A] is doubled, the reaction rate will increase by a factor of 2. The reaction is second order overall. The reaction is second order in [B]. k is the reaction rate constant. The reaction is first order in [A].

The reaction is second order overall.

The rate limiting step in a reaction is the slowest step in the reaction sequence. True False

True

Which statement below does not much affect the rate at which solid and liquid reaction occurs? Volume of reaction container Reactant concentrations and temperature Physical state of the reactants The presence of a catalyst

Volume of reaction container

The expression of Keq for the following reaction will not include __________. A (g) + B (s) ↔ C (g) + D(g) [C] [D] [A] [B] none of the above

[C]

Which of the following expressions is the correct equilibrium-constant expression for the reaction below? CO2 (s) + H2O (l) ↔ H+ (aq) + HCO3 - (aq) [CO2][H2O] / [H+][HCO3 -] [H+][HCO3 -] / [CO2] [H+][HCO3 -] [H+][HCO3 -] / [CO2][H2O] [CO2] / [H+][HCO3 -]

[H+][HCO3 -]

Which of the following expressions is the correct equilibrium-constant expression for the reaction below? (NH4)2Se (s) ⇌ 2NH3 (g) + H2Se (g) [(NH4)2Se] / [NH3]2[H2Se] [NH3]2[H2Se] / [(NH4)2Se] [NH3][H2Se] / [(NH4)2Se] 1 / [(NH4)2Se] [NH3]2[H2Se]

[NH3]2[H2Se]

Consider the following reaction at equilibrium: 2NH3 (g) ↔ N2 (g) + 3H2 (g) Δ H° = +92.4 kJ Le Châtelier's principle predicts that adding N2 (g) to the system at equilibrium will result in . removal of all of the H2 a lower partial pressure of N2 a decrease in the concentration of H2 an increase in the value of the equilibrium constant an increase in the concentration of H2

a decrease in the concentration of H2

Consider the following reaction at equilibrium: 2NH3 (g) ↔ N2 (g) + 3H2 (g) What effect you expect in the equilibrium when the following changes are made? some removal of NH3 from the reaction vessel (V and T constant) an increase in total pressure by the addition of helium gas (V and T constant) addition of some N2 to the reaction vessel (V and T constant) a decrease in the total pressure (T constant) a decrease in the total volume of the reaction vessel (T constant)

a decrease in the total pressure (T constant)

According to the equation below, which of the following will cause the concentration of H2SO4 to increase? 2NaHCO3 (s) + H2SO4 (aq) ⇄ Na2SO4 (aq) + 2H2O (l) + 2CO2 (g) removal of some CO2 (g) removal of some H2O (l) addition of some Na2SO4 (aq) addition of some NaHCO3 (s)

addition of some Na2SO4 (aq)

Which one of the following will change the value of an equilibrium constant? varying the initial concentrations of products varying the initial concentrations of reactants changing the volume of the reaction vessel adding other substances that do not react with any of the species involved in the equilibrium changing temperature

changing temperature

Name three main factors that can affect the rate of a chemical reaction. physical state of reactants concentration of reactants stirring rate concentration of products presence of catalyst

concentration of reactants, physical state of reactants, presence of catalyst

In general, as activation energy increases, reaction rate ___________ . stays the same regardless of whether the reaction is exothermic or endothermic goes down if the reaction is exothermic goes down regardless of whether the reaction is exothermic or endothermic goes down if the reaction is endothermic none of the above

goes down regardless of whether the reaction is exothermic or endothermic

In general, as temperature goes up, reaction rate _________. stays the same if the reaction is first order goes up if the reaction is endothermic goes up if the reaction is exothermic goes up regardless of whether the reaction is exothermic or endothermic stays the same regardless of whether the reaction is exothermic or endothermic

goes up regardless of whether the reaction is exothermic or endothermic

Consider the following reaction at equilibrium: 2CO2 (g) ↔ 2CO (g) + O2 (g) ∆H° = -514 kJ Le Châtelier's principle predicts that adding O2(g) to the reaction container will______ . decrease the partial pressure of CO2 increase the partial pressure of CO2 increase the partial pressure of CO at equilibrium decrease the value of the equilibrium constant increase the value of the equilibrium constant

increase the partial pressure of CO

The effect of a catalyst on an equilibrium is to ________ . increase the equilibrium constant so that products are favored increase the rate at which equilibrium is achieved without changing the composition of the equilibrium mixture slow the reverse reaction only increase the rate of the forward reaction only shift the equilibrium to the right

increase the rate at which equilibrium is achieved without changing the composition of the equilibrium mixture

Which of the following would lead to an increased rate of reaction for gaseous reactants? decreasing the partial pressures of the reactants increasing the temperature of the reactants decreasing the concentration of the reactants increasing the volume of the reaction container

increasing the temperature of the reactants

If the rate law for the reaction: 2A + 3B → products is first order in A and second order in B, then the rate law is rate = ________ . k[A]2[B]2 k[A]2[B]3 k[A]2[B] k[A][B] k[A][B]2

k[A][B]2

For a first-order reaction, a plot of _______ versus _______ is linear.

ln [A]t, t

Of the following, all are valid units for a reaction rate except ________. g/s mol/hr mol/L M/s mol/L-hr

mol/L

A burning splint will burn more vigorously in pure oxygen than in air because ________. oxygen is a reactant in combustion and concentration of oxygen is higher in pure oxygen than is in air oxygen is a catalyst for combustion nitrogen is a product of combustion and the system reaches equilibrium at a lower temperature oxygen is a product of combustion nitrogen is a reactant in combustion and its low concentration in pure oxygen catalyzes the combustion

oxygen is a reactant in combustion and concentration of oxygen is higher in pure oxygen than is in air

As the temperature of a reaction is increased, the rate of the reaction increases because the _______ . reactant molecules collide more frequently and with greater energy per collision reactant molecules collide less frequently activation energy is lowered reactant molecules collide more frequently with less energy per collision reactant molecules collide less frequently and with greater energy per collision

reactant molecules collide more frequently and with greater energy per collision

What is the molecularity of an elementary step, given its rate law is as follows: Rate = k[A]2[B]? bimolecular termolecular trimolecular unimolecular

termolecular

At equilibrium, . the rates of the forward and reverse reactions are equal all chemical reactions have ceased the rate constants of the forward and reverse reactions are equal the value of the equilibrium constant is 1 the limiting reagent has been consumed

the rates of the forward and reverse reactions are equal