Effect of Reactant Concentration on Reaction Rate questions

Which of the following shows the conditions needed to increase the rate of the reaction of magnesium with nitric acid at its start?

1. A Doubling the concentration of the acid and halving the surface area of magnesium.
2. B Doubling the concentration of the acid and doubling the surface area of magnesium.
3. C Halving the concentration of the acid and halving the surface area of magnesium.
4. D Halving the concentration of the acid and doubling the surface area of magnesium.

Four identical masses of zinc react with acids under different conditions.
Which of the following represents the reaction conditions that lead to the greatest increase in the rate of the reaction?
(form of zinc / acid used / volume of acid / concentration of acid)

1. A strips / HCl / 20 mL / 2 M
2. B powder / HCl / 20 mL / 2 M
3. C strips / H₂SO₄ / 40 mL / 1 M
4. D powder / H₂SO₄ / 20 mL / 2 M

Two cubes of calcium carbonate have the same volume. 25 mL of 1 M hydrochloric acid (at 40°C) were added to one of them.
What is the effect of adding 60 mL of 0.5 M hydrochloric acid (at 40°C) to the second cube, compared with the reaction of the first cube?

1. A The rate of reaction decreases and a larger amount is produced.
2. B The rate of reaction increases and a smaller amount is produced.
3. C The rate of reaction increases and a larger amount is produced.
4. D The rate of reaction decreases and a smaller amount is produced.

The opposite figure represents two experiments at their start.
Which of the following represents each of the two acids (1) and (2)?

1. A (1) : 0.01 M CH₃COOH , (2) : 0.01 M H₂SO₄
2. B (1) : 0.01 M HCl , (2) : 0.1 M HCl
3. C (1) : 0.1 M CH₃COOH , (2) : 0.1 M HCl
4. D (1) : 0.1 M H₂SO₄ , (2) : 0.01 M H₂SO₄

Curve (X) in the opposite graph represents the volume of gas produced with time when excess calcium carbonate reacts with 100 mL of 1 M hydrochloric acid. When the reaction was repeated using the same acid with another volume and concentration under the same conditions of pressure and temperature, curve (Y) was obtained.
What are the volume and the concentration of the acid that produced curve (Y)?

1. A 50 mL , 1 mol/L
2. B 25 mL , 1 mol/L
3. C 50 mL , 2 mol/L
4. D 25 mL , 2 mol/L

Curve (1) in the opposite graph represents the volume of gas given off with time when excess iron reacts with 100 mL of 0.1 M HCl acid, while curve (2) represents adding excess ..........

1. A scandium to 100 mL of 0.1 M HCl acid
2. B iron to 100 mL of 0.1 M H₂SO₄ acid
3. C scandium to 100 mL of 0.2 M CH₃COOH acid
4. D iron to 100 mL of 0.2 M HCl acid

Two experiments were carried out to measure the rate of oxygen gas given off from the decomposition of hydrogen peroxide under suitable conditions, as shown in the following table:
Experiment (X) : 100 mL of 2 M H₂O₂ solution
Experiment (Y) : 100 mL of 2 M H₂O₂ solution + 50 mL of 1 M H₂O₂ solution
Which graph represents the results of both experiments?

1. A A
2. B B
3. C C
4. D D

Four experiments (1), (2), (3) and (4) were carried out on the reaction of a fixed volume of nitric acid with identical pieces of calcium carbonate. The concentration of the acid was different from one experiment to another, and the opposite graph shows the volume of CO₂ gas produced in each experiment with time.
Which of the following can be concluded from this graph?

1. A The concentration of the acid used in experiment (3) is less than that used in experiment (1).
2. B The rate of reaction in experiment (4) is faster than in experiment (3).
3. C The concentration of the acid used in experiment (2) is greater than that used in experiment (1).
4. D The concentration of the acid used in experiment (2) is less than that used in experiment (4).

The opposite reversible reaction: 2N₂O(g) + 3O₂(g) ⇌ 4NO₂(g)
is represented by the equilibrium constant expression ..........

1. A Kc = ([2N₂O][3O₂]) / [4NO₂]
2. B Kc = ([N₂O]²[O₂]³) / [NO₂]⁴
3. C Kc = [4NO₂] / ([2N₂O][3O₂])
4. D Kc = [NO₂]⁴ / ([N₂O]²[O₂]³)

In the equilibrium reaction: 2KClO₃(s) ⇌ 2KCl(s) + 3O₂(g)
Which of the following represents the equilibrium constant of this reaction?

1. A Kc = [O₂]³
2. B Kc = 1 / [O₂]³
3. C Kc = [KClO₃]² / ([KCl]²[O₂]³)
4. D Kc = ([KCl]²[O₂]³) / [KClO₃]²

In the opposite equation: 2H₂(g) + O₂(g) ⇌ 2H₂O(v)
Which of the following represents the rate of the forward reaction (r₁)?

1. A r₁ = K [H₂O]²
2. B r₁ = K [H₂][O₂]
3. C r₁ = K [H₂]²[O₂]
4. D r₁ = K [H₂O]² / ([H₂]²[O₂])

In the equilibrium reaction: CO₂(g) + 2H₂O(v) ⇌ CH₄(g) + 2O₂(g)
Which of the following indicates that the reverse reaction is dominant?

1. A r₁ < r₂ , 1 > Kc
2. B r₁ < r₂ , 1 < Kc
3. C K₁ < K₂ , 1 > Kc
4. D K₁ < K₂ , 1 < Kc

An experiment was carried out on the reaction: 2A(g) + B(g) ⇌ C(g) , Kc = 1 × 10⁻²⁰
using 1 mol of each of the substances (A) and (B) in an empty 1 L vessel.
Which of the following represents the concentrations of the substances used when the state of equilibrium is reached?

1. A [A] < [B] < [C]
2. B [A] > [B] > [C]
3. C [A] = [B] < [C]
4. D [B] > [A] > [C]

The following reaction was carried out in a closed vessel (at STP):
2H₂O(v) + 2Cl₂(g) ⇌ 4HCl(g) + O₂(g) , Kc = 5 × 10⁻⁴
Which of the following represents the relation between the concentrations of the reaction substances when the state of equilibrium is reached?

1. A [Cl₂]²[H₂O]² < [O₂][HCl]⁴
2. B [O₂][HCl]⁴ < [H₂O]²[Cl₂]²
3. C [2Cl₂][2H₂O] < [O₂][4HCl]
4. D [O₂][4HCl] < [2H₂O][2Cl₂]

In the opposite equilibrium reaction: Cl₂(g) + 2NO(g) ⇌ 2NOCl(g) , Kc = 5
If [Cl₂] equals 1 M and [NO] equals 2 M, then [NOCl] equals ..........

1. A 0.8 M
2. B 0.89 M
3. C 4.5 M
4. D 10 M

0.2 mol of SO₂ gas were mixed with 0.2 mol of O₂ gas in a closed 1 L vessel, and at equilibrium the number of moles of SO₃ was 0.1 mol
What is the value of Kc for this reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)?

1. A 0.15
2. B 0.8
3. C 1.25
4. D 6.67

The opposite reaction was carried out in a closed 2 L vessel: A₂(g) + B₂(g) ⇌ 2AB(g)
At equilibrium the vessel contained:
• 0.7 mol of A₂
• 0.5 mol of B₂
• 0.2 mol of AB
What is the value of Kc for this reaction?

1. A 1.14
2. B 0.57
3. C 0.11
4. D 0.055

The opposite process was carried out in a closed vessel: I₂(v) ⇌ 2I(g) , Kc = 0.01
At equilibrium the number of moles of I₂ was 1 mol and the number of moles of I was 0.5 mol
What is the volume of the closed reaction vessel?

1. A 12.5 L
2. B 15 L
3. C 25 L
4. D 40 L

Given Kc for the reaction: A(g) + 2B(g) ⇌ C(g) + ⁵⁄₂ D(g) , Kc = 4
What is the value of Kc for the opposite reaction, assuming constant concentrations: 2C(g) + 5D(g) ⇌ 2A(g) + 4B(g)?

1. A 0.25
2. B 0.063
3. C 8
4. D 16

From the process: Cl₂(g) ⇌ 2Cl(g) , Kc = 1.13 × 10⁻⁶
What is the value of Kc for the reaction 2Cl(g) ⇌ Cl₂(g) at the same temperature?

1. A 8.85 × 10⁵
2. B 4.42 × 10⁵
3. C 2.26 × 10⁻⁶
4. D 1.13 × 10⁻⁶

In the reversible reaction: 2ICl(g) ⇌ Cl₂(g) + I₂(v)
the initial concentration of ICl gas was 0.75 M and the equilibrium constant Kc was 16
What percentage of ICl decomposed at equilibrium?

1. A 44%
2. B 88%
3. C 60%
4. D 80%

Iron(III) chloride solution was added to ammonium thiocyanate solution until the system reached the state of equilibrium.
What is the effect of adding excess ammonia solution to the equilibrium system?

1. A The system is activated in the reverse direction.
2. B The equilibrium is disturbed and the reaction stops.
3. C The concentration of ammonium thiocyanate increases.
4. D The concentration of ammonium thiocyanate decreases.

The following equation represents a reversible reaction in a state of equilibrium:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) , Kc = 1.2 × 10⁴
What happens to the direction of the reaction and to the value of Kc when more SO₂ is added to this reaction?

1. A The reaction shifts to the left / the value of Kc decreases
2. B The reaction shifts to the right / the value of Kc increases
3. C The reaction shifts to the right / the value of Kc does not change
4. D The reaction shifts to the left / the value of Kc does not change

In the reversible reaction: Ni(s) + 4CO(g) ⇌ Ni(CO)₄(s)
What is the effect of increasing [CO] on this equilibrium reaction?

1. A [Ni(CO)₄] decreases.
2. B [Ni] decreases.
3. C The mass of Ni decreases
4. D The value of Kc increases

In the equilibrium reaction: 4NH₃(g) + 5O₂(g) ⇌ 4NO(g) + 6H₂O(v)
What happens when NH₃ gas is withdrawn from the reaction vessel?

1. A The rate of the forward reaction increases.
2. B The reaction is activated to the right.
3. C The production of NO gas increases
4. D The reaction is activated to the left.

In the equilibrium reaction: N₂(g) + O₂(g) ⇌ 2NO(g)
When an amount of NO gas is removed from the reaction space,
which of the following graphs shows the system returning to the state of equilibrium at the same temperature?

1. A A
2. B B
3. C C
4. D D

When iron salt (X) is dissolved in water, a pale yellow solution forms:
(1) What is the colour of the precipitate formed when a strong base is added to the solution of salt (X)?
(2) What is the colour of the solution produced by adding a solution of thiocyanate ion to the solution of salt (X)?

The opposite graph shows the effect of adding more SCN⁻(aq) to the following equilibrium system:
Fe³⁺(aq) + SCN⁻(aq) ⇌ Fe(SCN)²⁺(aq)
(Fe³⁺ : pale yellow) , (SCN⁻ : colourless) , (Fe(SCN)²⁺ : red)
(1) Replace the numbers shown on the graph with the suitable ions.
(2) Describe the change in the colour of the reaction medium after adding SCN⁻(aq)

The opposite graph represents the change that happened (at 10 min) in the following reversible reaction:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) , ΔH = −192 kJ/mol
(1) What is the state of the reaction (at equilibrium or not at equilibrium) at 5 min? Explain.
(2) Which two substances are represented by the symbols (X) and (Y) on the graph when [O₂] is increased at 10 min? Explain.

The opposite graph represents the reversible reaction: A(g) ⇌ 2B(g)
Calculate the equilibrium constant of this reaction.

A reaction was carried out between 0.5 mol of H₂ gas and 0.5 mol of I₂ vapour (at 430°C) in a closed 1 L vessel,
according to the equation: H₂(g) + I₂(v) ⇌ 2HI(g) , Kc = 54.3
At equilibrium [H₂] was 0.107 M
Deduce the concentration of each of the following at equilibrium, with explanation.
(1) [I₂]
(2) [HI]

From the reversible reactions:
(1) Cl₂(g) + 2NO(g) ⇌ 2NOCl(g) , Kc = 3.7 × 10⁸
(2) 2HCl(g) ⇌ H₂(g) + Cl₂(g) , Kc = 2 × 10⁻⁷
(1) Write the equilibrium constant expression for reaction (1).
(2) State, with explanation, which of the forward and reverse reactions is dominant in:
(a) reaction (1).
(b) reaction (2).

The following two graphs represent the rates of the forward and reverse reactions («not in order») of a reversible gaseous reaction involving the gases: O₂ , SO₂ , SO₃
Write the numbers of the two curves that represent each of the following, with explanation:
(1) the concentration of O₂ gas
(2) the concentration of SO₃ gas

100 mL of 0.1 M HCl acid were added to 4 g of calcium carbonate powder, and the amount of CO₂ gas given off was recorded every 30 s in the following table:
[CaCO₃ = 100 g/mol]
Time (s) : 30 , 60 , 90 , 120 , 150 , 180 , 210 , 240
Amount of CO₂ gas given off (mL) : 40 , 70 , 88 , 101 , 110 , 112 , 112 , 112
(1) What happens to the rate of collisions between the reactant molecules with time?
(2) Why does the reaction stop at 180 s?

In the following equilibrium reaction: Ca(OH)₂(s) ⇌ CaO(s) + H₂O(v)
Which of the following changes leads to an increase in the mass of calcium oxide?

1. A Halving the mass of calcium oxide.
2. B Withdrawing 10 mL of water vapour.
3. C Doubling the mass of calcium hydroxide.
4. D Adding 10 mL of water vapour.

In which of the following reactions is the value of Kc equal to the concentration of the products?

1. A C(s) + O₂(g) ⇌ CO₂(g)
2. B CaCO₃(s) ⇌ CaO(s) + CO₂(g)
3. C H₂(g) + O₂(g) ⇌ 2H₂O(g)
4. D N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

The following table shows the number of moles of the reactants and products at a certain temperature in the following equilibrium reaction:
2NOCl(g) ⇌ 2NO(g) + Cl₂(g)
Number of moles at equilibrium: NOCl = 3 , NO = 1.5 , Cl₂ = 3
If the value of Kc for the reaction at the same temperature = 0.25, then the volume of the reaction vessel in litres is ..........

1. A 1
2. B 2
3. C 3
4. D 4

One mole of each of hydrogen and iodine gases were mixed at a certain temperature, and the volume of the vessel was 2 L
At equilibrium the amount remaining of each of hydrogen and iodine was 0.3 mol
Which of the following represents the equilibrium constant of this reaction at the same temperature?

1. A 4
2. B 16
3. C 0.8711
4. D 21.78

The opposite figure represents a reversible reaction.
Which of the following represents the equation of the reverse reaction of the reaction shown, and the value of its equilibrium constant?

1. A A ⇌ C , and the value of Kc = 0.75
2. B C ⇌ A , and the value of Kc = 1.33
3. C A ⇌ C , and the value of Kc = 1.33
4. D C ⇌ A , and the value of Kc = 0.75

In the equilibrium reaction: A(g) + B(g) ⇌ 2C(g)
Given that the concentrations of the reactants and products at 200°C in a 1 L vessel are:
[A] = 0.200 M , [B] = 3.00 M , [C] = 0.500 M
Which of the following represents the number of moles of A that must be added so that [C] = 0.700 M at the same temperature?

1. A 0.225 mol
2. B 0.305 mol
3. C 0.417 mol
4. D 0.610 mol

The following equilibrium reaction at a certain temperature:
2A(aq) + 3B(aq) ⇌ 2C(aq) + 3D(aq)
The concentrations of the reactants and products at equilibrium are: [A] = 1.5 M , [B] = 2.3 M , [C] = 3 M , [D] = 4.5 M
When the concentration of substance (A) was increased and the reaction reached equilibrium again at the same temperature, the concentrations at equilibrium became: [A] = 2.5 M , [C] = 4 M , [D] = 6 M
Which of the following represents the concentration of substance (B) at equilibrium?

1. A 29.96 M
2. B 6.98 M
3. C 3.83 M
4. D 2.64 M

0.8 mol of substance (A) was placed in a 1 L vessel, and when the state of equilibrium was reached according to the following equation: A(aq) ⇌ 2B(aq), it was found that 0.4 mol of substance (A) had changed into (B).
Which of the following graphs represents the state of equilibrium and the equilibrium constant of this reaction?

1. A A
2. B B
3. C C
4. D D

To which of the following reactions does the law of mass action apply?

1. A HCl(aq) + KOH(aq) = KCl(aq) + H₂O(l) (in an open vessel)
2. B 2NaNO₃(s) = 2NaNO₂(s) + O₂(g) (in an open vessel)
3. C CaCl₂(aq) + (NH₄)₂CO₃(aq) = 2NH₄Cl(aq) + CaCO₃(s) (in a closed vessel)
4. D CaCO₃(s) = CaO(s) + CO₂(g) (in a closed vessel)

The following reaction: NO + ½O₂ ⇌ NO₂ takes place in a closed vessel at 25°C
When the state of equilibrium is reached, the value of Kc = 6.33
At a certain moment the amount of substance of NO = 0.3 mol, of O₂ = 0.3 mol and of NO₂ = 0.5 mol in a 2 L vessel at 25°C
Which of the following represents the state of the reaction at this moment?

1. A The reaction is at equilibrium and the equilibrium constant > 6.33
2. B The reaction is not at equilibrium and the equilibrium constant < 6.33
3. C The reaction is faster in the reverse direction.
4. D The reaction is faster in the forward direction.

In the following equilibrium reaction: 2NO + O₂ ⇌ 2NO₂
Which of the following is correct?

1. A O₂ and NO react in equal mass ratios.
2. B The rate of formation of NO₂ equals twice the rate of consumption of O₂
3. C The rate of consumption of NO₂ equals the rate of formation of O₂
4. D The volume of the reactants equals the volume of the products.

The following equation represents the reaction between nitric oxide and hydrogen under certain conditions:
2NO(g) + 2H₂(g) ⇌ N₂(g) + 2H₂O(v)
When 0.1 mol of nitric oxide was mixed with 0.05 mol of hydrogen in a closed 1 L vessel at a certain temperature, the number of moles of nitric oxide in the vessel at equilibrium was found to be 0.062 mol
Which of the following represents the value of Kc for this reaction at the same temperature?

1. A 1.86
2. B 3.13
3. C 49.56
4. D 94.62

The following equilibrium reaction at a certain temperature:
CH₃COOH(aq) + C₂H₅OH(aq) ⇌ CH₃COOC₂H₅(l) + H₂O(l) , Kc = 10⁻³
At equilibrium the concentration of acetic acid was 0.5 M and the concentration of ethyl alcohol was 0.01 M
The concentration of ethyl acetate equals ..........

1. A 5 × 10⁻⁶ M
2. B 1 × 10⁻⁶ M
3. C 0.5 × 10⁻⁴ M
4. D 5 × 10⁻³ M

Four flasks of equal volume contained the amounts shown in the following figures:
The correct order of the reactions according to their speed (the choices are in the figure) ..........

1. A A
2. B B
3. C C
4. D D

In the equilibrium reaction: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
Given that the numbers of moles of PCl₅ , PCl₃ and Cl₂ at equilibrium are (0.008 , 0.0114 , 0.0114) respectively
and the volume of the vessel = 10 L, then the value of the equilibrium constant Kc is ..........

1. A 615.5
2. B 1.62 × 10⁻³
3. C 16.24 × 10⁻³
4. D 61.55

When ammonia gas was prepared from its elements at a certain temperature,
it was found at equilibrium that: [N₂] = 0.5 M , [H₂] = 0.7 M , Kc = 3.7 × 10⁻⁴
so [NH₃] = ..........

1. A 7.97 × 10⁻³ M
2. B 63.36 × 10⁻⁶ M
3. C 3.9 × 10⁻² M
4. D 7.8 × 10⁻⁴ M

When equal concentrations of H₂ and A₂ were mixed, the following equilibrium took place: H₂(g) + A₂(g) ⇌ 2HA(g)
If [HA] equals 1.563 M at equilibrium and the equilibrium constant equals 40,
then [A₂] equals ..........

1. A 0.247 M
2. B 0.039 M
3. C 62.52 M
4. D 42.52 M

The opposite graph represents the equilibrium state A + 3B ⇌ 2C
so the value of Kc equals ..........

1. A 6.66
2. B 14.81
3. C 0.9
4. D 15.49

In the reaction: I₂(g) + H₂(g) ⇌ 2HI(g)
If the equilibrium constant of this reaction equals 1.55 and the concentration of hydrogen iodide is (1.035 M),
then the concentrations of hydrogen and iodine respectively are ..........

1. A [H₂] = 0.79 M , [I₂] = 0.83 M
2. B [H₂] = 0.83 M , [I₂] = 0.79 M
3. C [H₂] = 0.83 M , [I₂] = 0.83 M
4. D [H₂] = 0.135 M , [I₂] = 0.135 M

A 2 L solution contains 0.6 mol of HA, 0.7 mol of BOH, 1 mol of BA and 100 mol of water:
HA(aq) + BOH(aq) ⇌ BA(aq) + H₂O(l)
The value of the equilibrium constant of the previous reaction is ..........

1. A 238
2. B 476
3. C 2.38
4. D 4.76

When a solution of substance (Y) is added to a pale yellow solution of substance (X), a solution of a certain colour forms,
and when more of the solution of substance (Y) is added to the same reaction, the colour produced becomes deeper.
The two substances (X) and (Y) are ..........

1. A (X) : FeCl₃ , (Y) : NH₄SCN
2. B (X) : NH₄SCN , (Y) : FeCl₃
3. C (X) : NH₄OH , (Y) : FeCl₃
4. D (X) : FeCl₃ , (Y) : NH₄OH

In the reaction: N₂O₄(g) ⇌ 2NO₂(g)
(N₂O₄ : colourless) , (NO₂ : reddish brown)
When more N₂O₄ gas is added, ..........

1. A the colour increases and the value of Kc stays constant.
2. B the colour increases and the value of Kc increases
3. C the colour decreases and the value of Kc stays constant.
4. D the colour decreases and the value of Kc decreases

In the opposite equilibrium reaction: 4NH₃(g) + 3O₂(g) ⇌ 2N₂(g) + 6H₂O(v)
When a little of the mixture (O₂ + 2N₂(g)) is added to the previous reaction, it is activated in the ..........

1. A forward direction and [NH₃] increases.
2. B reverse direction and [O₂] decreases.
3. C reverse direction and [NH₃] increases.
4. D forward direction and [N₂] decreases.

In the two opposite equilibrium reactions:
(1) N₂O₄(g) ⇌ 2NO₂(g) , Kc₁
(2) 2NO₂(g) ⇌ N₂O₄(g) , Kc₂
the mathematical relation between the equilibrium constants is ..........

1. A Kc₁ + Kc₂ = 1
2. B Kc₁ × Kc₂ = 1
3. C Kc₁ ÷ Kc₂ = 1
4. D Kc₁ − Kc₂ = 1