[Maximum number: 4]

Ethane-1,2-diol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ , has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

(a)

(i)

$\Delta S^{\ominus}$ for the reaction in (b)(i) is $-620.1 \mathrm{JK}^{-1}$ . Comment on the decrease in entropy.

[ 1 ]

(ii)

Calculate the value of $\Delta G^{\ominus}$ , in kJ , for this reaction at 298 K using your answer to (b)(i). (If you did not obtain an answer to (b)(i), use -244.0 kJ , but this is not the correct value.)

[ 2 ]

(iii)

Comment on the statement that the reaction becomes less spontaneous as temperature is increased.

[ 1 ]

[Maximum number: 2]

Urea, $\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}$ , is excreted by mammals and can be used as a fertilizer.

(a)

The combustion of urea produces water, carbon dioxide and nitrogen.

Formulate a balanced equation for the reaction.

[ 2 ]

[Maximum number: 4]

Urea, $\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}$ , is excreted by mammals and can be used as a fertilizer.

(a)

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

2 \mathrm{NH}_{3}(\mathrm{~g})+\mathrm{CO}_{2}(\mathrm{~g}) \rightleftharpoons\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{CO}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \quad \Delta H<0

[ 2 ]

(i)

Determine an approximate order of magnitude for $K_{\mathrm{c}}$ , using sections 1 and 2 of the data booklet. Assume $\Delta G^{\ominus}$ for the forward reaction is approximately +50 kJ at 298 K .

[ 2 ]

(b)

The combustion of urea produces water, carbon dioxide and nitrogen.

Formulate a balanced equation for the reaction.

[ 2 ]

[Maximum number: 1]

Ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}$ , reacts with oxygen in welding torches.

(a)

Write an equation for the complete combustion of ethyne.

[ 1 ]

[Maximum number: 1]

Ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}$ , reacts with oxygen in welding torches.

(a)

Write an equation for the complete combustion of ethyne.

[ 1 ]

[Maximum number: 7]

Ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$ , is used as a high nitrogen fertilizer.

(a)

Cold packs contain ammonium nitrate and water separated by a membrane.

[ 5 ]

(i)

Calculate the standard entropy change, $\Delta S^{\ominus}$ , for the dissolution of ammonium nitrate.

\begin{aligned} \mathrm{S}^{\ominus} \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{~s}) & =151.1 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1} \\ \mathrm{~S}^{\ominus} \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{aq}) & =259.8 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1} \end{aligned}

[ 1 ]

(ii)

Calculate the standard Gibbs free energy change, $\Delta G^{\ominus}$ , in $\mathrm{kJ} \mathrm{mol}^{-1}$ , for the dissolution of ammonium nitrate at 298 K . Use sections 1 and 19 of the data booklet as well as your answer for question part (d)(v).

If you did not obtain an answer in (d)(v), use $102.3 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$ , although this is not the correct answer.

[ 1 ]

(iii)

Calculate the value of the equilibrium constant for the dissolution of ammonium nitrate at 298 K using the answer to question part (d)(vi) and section 1 of the data booklet.

\mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{~s}) \rightleftharpoons \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{aq})

If you did not obtain an answer in (d)(vi), use $-7.84 \mathrm{~kJ} / \mathrm{mol}$ , although this is not the correct answer.

[ 2 ]

(iv)

Deduce, with a reason, the position of the equilibrium.

[ 1 ]

(b)

Solid ammonium nitrate can decompose to gaseous dinitrogen monoxide and liquid water.

[ 2 ]

(i)

Predict, with a reason, the signs for the entropy change, $\Delta S^{\ominus}$ , and Gibbs free energy change, $\Delta G^{\ominus}$ , of the reaction.

Entropy change:
Gibbs free energy change:

[ 2 ]

[Maximum number: 1]

Which hydrocarbon would produce equal numbers of moles of $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ upon complete combustion?

A

$\mathrm{CH}_{4}$

B

$\mathrm{C}_{2} \mathrm{H}_{2}$

C

$\mathrm{C}_{3} \mathrm{H}_{8}$

D

$\mathrm{C}_{4} \mathrm{H}_{8}$

[Maximum number: 1]

Which expression gives the sum of all the coefficients for the general equation for the complete combustion of hydrocarbons?

{ }_{-} \mathrm{C}_{x} \mathrm{H}_{y}(\mathrm{~g})+\ldots \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \ldots \mathrm{CO}_{2}(\mathrm{~g})+\ldots \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

A

$1+x+\frac{y}{4}$

B

$1+x+\frac{y}{2}$

C

$1+2 x+\frac{3 y}{4}$

D

$1+2 x+\frac{3 y}{2}$

[Maximum number: 1]

What is the sum of the integer coefficients when propene undergoes complete combustion?

-\mathrm{C}_{3} \mathrm{H}_{6}(\mathrm{~g})+\ldots \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \underline{\hspace{1.8em}} \mathrm{CO}_{2}(\mathrm{~g})+\underline{\hspace{0.9em}} \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

A

11

B

17

C

21

D

23

[Maximum number: 1]

The equation for the complete combustion of propene, $\mathrm{C}_{3} \mathrm{H}_{6}$ , is shown below.

2 \mathrm{C}_{3} \mathrm{H}_{6}(\mathrm{~g})+9 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 6 \mathrm{CO}_{2}(\mathrm{~g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

Which mixture, when ignited, will lead to incomplete combustion and the formation of CO(g) ?

A

$2 \mathrm{dm}^{3}$ of propene and $10 \mathrm{dm}^{3}$ of oxygen

B

$0.5 \mathrm{dm}^{3}$ of propene and $2.3 \mathrm{dm}^{3}$ of oxygen

C

$1 \mathrm{dm}^{3}$ of propene and $4 \mathrm{dm}^{3}$ of oxygen

D

$3 \mathrm{dm}^{3}$ of propene and $14 \mathrm{dm}^{3}$ of oxygen