DP Chemistry Questionbank

CT values are influenced by temperature and by pH. The table below shows the CT values for chlorine needed to achieve 99% inactivation of a specific bacterium at stated values of pH and temperature.

(i) With reference to the temperature data in the table, suggest why it may be more difficult to treat water effectively with chlorine in cold climates.

(ii) Sketch a graph on the axes below to show how the CT value (at any temperature) varies with pH.

(iii) Comment on the relative CT values at pH 6.0 and pH 9.0 at each temperature.

(iv) Chlorine reacts with water as follows:

Cl₂ (g) + H₂O (l) $\rightleftharpoons$ HOCl (aq) + HCl (aq)

HOCl (aq) $\rightleftharpoons$ OCl⁻ (aq) + H⁺ (aq)

Predict how the concentrations of each of the species HOCl (aq) and OCl⁻ (aq) will change if the pH of the disinfected water increases.

What happens when the temperature of the following equilibrium system is increased? 

CO(g) + 2H₂(g)  CH₃OH(g)         ΔH^θ = -91kJ

Ethane-1,2-diol can be formed according to the following reaction.

2CO (g) + 3H₂ (g) $\rightleftharpoons$ HOCH₂CH₂OH (g)

(i) Deduce the equilibrium constant expression, K_c, for this reaction.

(ii) State how increasing the pressure of the reaction mixture at constant temperature will affect the position of equilibrium and the value of K_c.

Position of equilibrium:

K_c:

(iii) Calculate the enthalpy change, ΔH^θ, in kJ, for this reaction using section 11 of the data booklet. The bond enthalpy of the carbon–oxygen bond in CO (g) is 1077kJmol^-1.

(iv) The enthalpy change, ΔH^θ, for the following similar reaction is –233.8 kJ.

2CO(g) + 3H₂(g) $\rightleftharpoons$ HOCH₂CH₂OH (l)

Deduce why this value differs from your answer to (a)(iii).

Consider the equilibrium between N₂O₄(g) and NO₂(g).

N₂O₄(g) $\rightleftharpoons$ 2NO₂(g)          ΔH = +58 kJ$$mol⁻¹

Which changes shift the position of equilibrium to the right?

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

Hydrazine reacts with water in a similar way to ammonia. Deduce an equation for the reaction of hydrazine with water.

Explain the effect of a large amount of aspirin on the pH of blood.

Outline, giving the appropriate equation(s), how increasing levels of carbon dioxide will affect the pH of the oceans.

What is the equilibrium constant expression, K_c, for the following reaction?

2NH₃(g) + 2O₂(g) $\rightleftharpoons$ N₂O(g) + 3H₂O(g)

A.     $\frac{3\left[{\text{H}}_2\text{O}\right]\left[{\text{N}}_2\text{O}\right]}{2\left[\text{N}{\text{H}}_3\right]2\left[{\text{O}}_2\right]}$

B.     $\frac{{\left[\text{N}{\text{H}}_3\right]}^2{\left[{\text{O}}_2\right]}^2}{\left[{\text{N}}_2\text{O}\right]{\left[{\text{H}}_2\text{O}\right]}^3}$

C.     $\frac{2\left[\text{N}{\text{H}}_3\right]2\left[{\text{O}}_2\right]}{3\left[{\text{H}}_2\text{O}\right]\left[{\text{N}}_2\text{O}\right]}$

D.     $\frac{\left[{\text{N}}_2\text{O}\right]{\left[{\text{H}}_2\text{O}\right]}^3}{{\left[\text{N}{\text{H}}_3\right]}^2{\left[{\text{O}}_2\right]}^2}$

Deduce the equilibrium constant expression, K_c, for the decomposition of PCl₅(g).

Deduce, giving a reason, the factor responsible for establishing the new equilibrium after 14 minutes.

The equilibrium expression for O₂ exchange between the atmosphere and ocean is O₂(g) $\rightleftharpoons$ O₂(aq). Identify one factor which shifts the equilibrium to the right.

Describe how large amounts of CO₂ could reduce the pH of the ocean using an equation to support your answer.

Ammonia reacts reversibly with water.

NH₃(g) + H₂O(l) $\rightleftharpoons$ NH₄⁺(aq) + OH⁻(aq)

Explain the effect of adding H⁺(aq) ions on the position of the equilibrium.

Suggest one improvement to the investigation.

What is correct when temperature increases in this reaction at equilibrium?

$2\mathrm{NOCl} \left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{NO} \left(\mathrm{g}\right)+{\mathrm{Cl}}_2 \left(\mathrm{g}\right)$    $∆H^{⦵}=+75.5 \mathrm{kJ}$

The equilibrium constant, $K_{\mathrm{c}}$, for the conversion of A to B is $1.0\times {10}^8$ in water at $298 \mathrm{K}$.

Deduce, giving a reason, which compound, A or B, is present in greater concentration when equilibrium is reached.

The equilibrium constant, $K_{\mathrm{c}}$, for the conversion of A to B is $1.0\times {10}^8$ in water at $298 \mathrm{K}$.

Deduce, giving a reason, which compound, A or B, is present in greater concentration when equilibrium is reached.

State the $K_{\mathrm{a}}$ expression for ethanoic acid.

State the equilibrium constant expression, K_c , for this reaction.

What will happen if the pressure is increased in the following reaction mixture at equilibrium?

CO₂ (g) + H₂O (l) $\rightleftharpoons$ H⁺ (aq) + HCO₃⁻ (aq)

A. The equilibrium will shift to the right and pH will decrease.

B. The equilibrium will shift to the right and pH will increase.

C. The equilibrium will shift to the left and pH will increase.

D. The equilibrium will shift to the left and pH will decrease.

The following reaction was allowed to reach equilibrium at 761 K.

H₂ (g) + I₂ (g) $\rightleftharpoons$ 2HI (g)               ΔH^θ < 0

Outline the effect, if any, of each of the following changes on the position of equilibrium, giving a reason in each case.

Which changes produce the greatest increase in the percentage conversion of methane?

CH₄(g) + H₂O (g) $\rightleftharpoons$ CO (g) + 3H₂(g)

Sulfur dioxide reacts with oxygen to form sulfur trioxide.

2SO₂ (g) + O₂ (g) $\rightleftharpoons$ 2SO₃ (g)           ΔH = −197 kJ

Which change increases the value of K_c?

A.  increasing the temperature

B.  decreasing the temperature

C.  decreasing [SO₂ (g)]

D.  decreasing [SO₃ (g)]

State the expression for K_c for this stage of the reaction.

State the expression for K_c for this stage of the reaction.

Consider the following equilibrium reaction:

2SO₂(g) + O₂(g) $\rightleftharpoons$ 2SO₃(g)

State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.

State the equilibrium constant expression, K_c, for the reaction above.

What occurs when the pressure on the given equilibrium is increased at constant temperature?

N₂(g) + O₂(g) $\rightleftharpoons$ 2NO(g)     ΔH = +180 kJ

A.     K_c increases and the position of equilibrium moves to the right.

B.     K_c stays the same and the position of equilibrium is unchanged.

C.     K_c stays the same and the position of equilibrium moves to the left.

D.     K_c decreases and the position of equilibrium moves to the left.

What is the effect of increasing the temperature in this reaction?

CO₂(g) + H₂O(l) $\rightleftharpoons$ H⁺(aq) + HCO₃⁻(aq)     ΔH < 0

A.     The pH will decrease.

B.     The pH will increase.

C.     CO₂ pressure will decrease.

D.     The equilibrium position will shift to the right.

State the equilibrium constant expression, K_c.

Predict, with a reason, the effect on the equilibrium constant, K_c, when the temperature is increased.

Nitrogen oxide is in equilibrium with dinitrogen dioxide.

2NO(g) $\rightleftharpoons$ N₂O₂(g)     ΔH^Θ < 0

Deduce, giving a reason, the effect of increasing the temperature on the concentration of N₂O₂.

The equilibrium constant for N₂(g) + 3H₂(g) $\rightleftharpoons$ 2NH₃(g) is K.

What is the equilibrium constant for this equation?

2N₂(g) + 6H₂(g) $\rightleftharpoons$ 4NH₃(g)

A.     K

B.     2K

C.     K²

D.     2K²

Urea can also be made by the direct combination of ammonia and carbon dioxide gases.

                                   2NH₃(g) + CO₂(g) $\rightleftharpoons$ (H₂N)₂CO(g) + H₂O(g)     ΔH < 0

Predict, with a reason, the effect on the equilibrium constant, K_c, when the temperature is increased.

Which factor does not affect the position of equilibrium in this reaction?

2NO₂(g) $\rightleftharpoons$ N₂O₄(g)     ΔH = −58 kJ mol⁻¹

A.     Change in volume of the container

B.     Change in temperature

C.     Addition of a catalyst

D.     Change in pressure

Distinguish between the terms reaction quotient, Q, and equilibrium constant, K_c.

The equilibrium constant, K_c, is 0.282 at temperature T.

Deduce, showing your work, the direction of the initial reaction.

The equilibrium 2H₂ (g) + N₂(g) $\rightleftharpoons$ N₂H₄(g) has an equilibrium constant, K, at 150 °C. 

What is the equilibrium constant at 150 °C, for the reverse reaction?

N₂H₄(g) $\rightleftharpoons$ 2H₂ (g) + N₂(g)

A.  K

B.  K⁻¹

C.  −K

D.  2K

A reversible reaction has a reaction quotient, Q, of 4.5 and equilibrium constant, K_c, of 6.2.

2A (g) $\rightleftharpoons$ A₂(g)

Which statement describes the reaction at this time?

A.  The system has reached equilibrium.

B.  The rate of the forward reaction is greater than the rate of the reverse reaction.

C.  The concentration of reactant is greater than the concentration of product.

D.  At equilibrium, the concentration of reactant is greater than the concentration of product.

State the equilibrium constant expression, K_c, for this reaction.

State the equilibrium constant expression, K_c, for this reaction.

$\frac{1}{2}$Cl₂(g) + $\frac{1}{2}{\text{I}}_2$(g) $\rightleftharpoons$ $\text{I}$Cl (g)    K_c = 454

What is the K_c value for the reaction below?

2 $\text{I}$Cl (g) $\rightleftharpoons$ Cl₂(g) + ${\text{I}}_{\text{2}}$(g)

A.  $2\times 454$

B.  $\frac{1}{2\times 454}$

C.  ${454}^2$

D.  $\frac{1}{{454}^2}$

Which species are acids in the equilibrium below?

CH₃NH₂ + H₂O $\rightleftharpoons$ CH₃NH₃⁺ + OH^–

A.  CH₃NH₂ and H₂O

B.  H₂O and CH₃NH₃⁺

C.  H₂O and OH^–

D.  CH₃NH₂ and CH₃NH₃⁺

0.200 mol sulfur dioxide, 0.300 mol oxygen and 0.500 mol sulfur trioxide were mixed in a 1.00 dm³ flask at 1000 K.

Predict the direction of the reaction showing your working.

Consider the reaction:

2N₂O (g) $\rightleftharpoons$ 2N₂ (g) + O₂ (g)

The values of K_c at different temperatures are:

Which statement is correct at higher temperature?

A.   The forward reaction is favoured.

B.   The reverse reaction is favoured.

C.   The rate of the reverse reaction is greater than the rate of the forward reaction.

D.   The concentration of both reactants and products increase.

0.200 mol sulfur dioxide, 0.300 mol oxygen and 0.500 mol sulfur trioxide were mixed in a 1.00 dm³ flask at 1000 K.

Predict the direction of the reaction showing your working.

At equilibrium, the concentrations of chlorine and iodine are both 0.02 mol dm^–3.

$\frac{1}{2}$Cl₂ (g) + $\frac{1}{2}$${\text{I}}_2$ (g) $\rightleftharpoons$ $\text{I}$Cl (g)       K_c = 454

What is the concentration of iodine monochloride, $\text{I}$Cl?

A.  $\frac{454}{0.02}$

B.  $454\times 0.02$

C.  $\frac{454}{0.04}$

D.  $454\times 0.04$

The equilibrium constant, K_c, for the reaction 2A + 4B $\rightleftharpoons$ 2C + 4D has a value of 4.0. What is the value of K_c for the reaction below at the same temperature?

C + 2D $\rightleftharpoons$ A + 2B

A.  0.25

B.  0.50

C.  1.0

D.  16

0.50 mol of ${\text{I}}_2$ (g) and 0.50 mol of Br₂(g) are placed in a closed flask. The following equilibrium is established.

${\text{I}}_2$(g) + Br₂(g) $\rightleftharpoons$ 2$\text{I}$Br (g)

The equilibrium mixture contains 0.80 mol of $\text{I}$Br (g). What is the value of K_c?

A.  0.64

B.  1.3

C.  2.6

D.  64

Deduce the expression for the equilibrium constant, K_c, for this equation.

Explain why an increase in pressure shifts the position of equilibrium towards the products and how this affects the value of the equilibrium constant, K_c.

With reference to the reaction quotient, Q, explain why the percentage yield increases as the pressure is increased at constant temperature.

Demonstrate that your answer to (b)(i) is consistent with the effect of an increase in temperature on the percentage yield, as shown in the graph.

Deduce the expression for the equilibrium constant, K_c, for this equation.

State the equilibrium constant expression, K_c, for this reaction.

Comment on why peracetic acid, CH3COOOH, is always sold in solution with ethanoic acid and hydrogen peroxide.

H₂O₂ (aq) + CH₃COOH (aq) ⇌ CH₃COOOH (aq) + H₂O (l)

A solution of bleach can be made by reacting chlorine gas with a sodium hydroxide solution.

Cl₂ (g) + 2NaOH (aq) ⇌ NaOCl (aq) + NaCl (aq) + H₂O (l)

Suggest, with reference to Le Châtelier’s principle, why it is dangerous to mix vinegar and bleach together as cleaners.

When a bottle of carbonated water is opened, these equilibria are disturbed.

State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).

Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)

Lead(II) chloride, PbCl₂, has very low solubility in water.

PbCl₂ (s) $\rightleftharpoons$ Pb²⁺ (aq) + 2Cl⁻ (aq)

Explain why the presence of chloride ions in beverages affects lead concentrations.

Suggest why the relationship between time and lead concentration for Cola at 16 °C is not linear.

Consider the following equilibrium reaction.

2N₂O (g) + O₂ (g) $\rightleftharpoons$ 4NO (g)        ΔH = +16 kJ

Which change will move the equilibrium to the right?

A. Decrease in pressure

B. Decrease in temperature

C. Increase in [NO]

D. Decrease in [O₂]

K_c for 2N₂O (g) $\rightleftharpoons$ 2N₂ (g) + O₂ (g) is 7.3 × 10³⁴.

What is K_c for the following reaction, at the same temperature?

N₂ (g) + $\frac{1}{2}$O₂ (g) $\rightleftharpoons$ N₂O (g)

A. 7.3 × 10³⁴

B. $\frac{1}{\sqrt{7.3\times {10}^{34}}}$

C. $\frac{1}{7.3\times {10}^{34}}$

D. $\frac{1}{2\times 7.3\times {10}^{34}}$

A solution of bleach can be made by reacting chlorine gas with a sodium hydroxide solution.

Cl2 (g) + 2NaOH (aq) $\rightleftharpoons$ NaOCl (aq) + NaCl (aq) + H₂O (l)

Suggest, with reference to Le Châtelier’s principle, why it is dangerous to mix vinegar and bleach together as cleaners.

Comment on why peracetic acid, CH₃COOOH, is always sold in solution with ethanoic acid and hydrogen peroxide.

H₂O₂ (aq) + CH₃COOH (aq) $\rightleftharpoons$ CH₃COOOH (aq) + H₂O (l)

Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)

When a bottle of carbonated water is opened, these equilibria are disturbed.

State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).

Suggest why the relationship between time and lead concentration for Cola at 16 °C is not linear.

Lead(II) chloride, PbCl2, has very low solubility in water.

PbCl₂ (s) $\rightleftharpoons$ Pb²⁺ (aq) + 2Cl⁻ (aq)

Explain why the presence of chloride ions in beverages affects lead concentrations.

What is the equilibrium constant expression for the following equation?

2NO₂ (g) + F₂ (g) $\rightleftharpoons$ 2NO₂F (g)

A. $\frac{2[\text{N}{\text{O}}_2\text{F]}}{2[\text{N}{\text{O}}_2]+[{\text{F}}_2]}$

B. $\frac{2[\text{N}{\text{O}}_2\text{F]}}{2[\text{N}{\text{O}}_2][{\text{F}}_2]}$

C. $\frac{{[\text{N}{\text{O}}_2\text{]}}^2\text{[}{\text{F}}_2\text{]}}{{[\text{N}{\text{O}}_2\text{F}]}^2}$

D. $\frac{{[\text{N}{\text{O}}_2\text{F]}}^2}{{[\text{N}{\text{O}}_2]}^2[{\text{F}}_2]}$

K_c for 2N₂O (g) $\rightleftharpoons$ 2N₂ (g) + O₂ (g) is 7.3 × 10³⁴.

What is K_c for the following reaction, at the same temperature?

N₂ (g) + $\frac{1}{2}$O₂ (g) $\rightleftharpoons$ N₂O (g)

A. 7.3 × 10³⁴

B. $\frac{1}{\sqrt{7.3\times {10}^{34}}}$

C. $\frac{2}{7.3\times {10}^{34}}$

D. $\frac{1}{2\times 7.3\times {10}^{34}}$

The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H⁺], and on K_a, of increasing the temperature.

What effect does increasing both pressure and temperature have on the equilibrium constant, K_c?

N₂ (g) + 3H₂ (g) $\rightleftharpoons$ 2NH₃ (g)           ΔH = −45.9 kJ

A.  Decreases

B.  Increases

C.  Remains constant

D.  Cannot be predicted as effects are opposite

The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H⁺], and on the equilibrium constant, of increasing the temperature.