[Maximum number: 2]

Calcium, magnesium and radium are Group 2 elements. Radium follows the same trends as the other members of Group 2.

(a)

Cold water reacts slowly with a piece of Mg to produce bubbles of $\mathrm{H}_{2}(\mathrm{~g})$ . Cold water reacts rapidly with burning Mg to produce $\mathrm{H}_{2}(\mathrm{~g})$ in an explosive mixture.

\mathrm{Mg}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2}+\mathrm{H}_{2}

Explain why the rate of reaction of cold water with burning magnesium is greater.

[ 2 ]

[Maximum number: 3]

The elements sodium to chlorine, in the third period, all form oxides.

(a)

$\mathrm{SO}_{3}$ is produced by the reaction between $\mathrm{SO}_{2}$ and $\mathrm{O}_{2}$ in the Contact process. A dynamic equilibrium is established.

2 \mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{SO}_{3}(\mathrm{~g}) \quad \Delta H=-196 \mathrm{~kJ} \mathrm{~mol}^{-1}

[ 3 ]

(i)

Explain why the gradients of the $\mathrm{SO}_{2}$ and $\mathrm{O}_{2}$ lines decrease with time.

[ 2 ]

(ii)

Suggest a reason why the initial gradient of the $\mathrm{SO}_{2}$ line is steeper than that of the $\mathrm{O}_{2}$ line.

[ 1 ]

[Maximum number: 3]

Sulfuric acid is manufactured by the Contact process.
One stage in this process is the conversion of sulfur dioxide into sulfur trioxide in the presence of a heterogeneous catalyst of vanadium(V) oxide, $\mathrm{V}_{2} \mathrm{O}_{5}$ .

(a)

(i)

State and explain the effect of increasing temperature on the rate of production of $\mathrm{SO}_{3}$ .

[ 3 ]

[Maximum number: 1]

The rate of the reaction $\mathrm{H}_{2}(\mathrm{~g})+\mathrm{I}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{HI}(\mathrm{g})$ is studied.

(a)

A small amount of $\mathrm{H}_{2}(\mathrm{~g})$ is mixed with a large excess of $\mathrm{I}_{2}(\mathrm{~g})$ at a temperature of 400 K and the reaction is monitored. The graph obtained is shown.

[ 1 ]

(i)

Suggest why a large excess of $\mathrm{I}_{2}(\mathrm{~g})$ is used in this experiment.

[ 1 ]

[Maximum number: 12]

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$ , can be used as a rocket fuel and is stored as a liquid. It reacts exothermically with oxygen to give only gaseous products.

The enthalpy change of a reaction such as that between hydrazine and oxygen may be calculated by using standard enthalpy changes of formation.

(a)

Hydrazine reacts with oxygen according to the following equation.

\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

(i)

Although the above reaction is highly exothermic, hydrazine does not burn spontaneously in oxygen.
Suggest a reason for this.

[Maximum number: 1]

A student carries out four experiments to investigate the rate of reaction between 3.0 g of calcium carbonate and hydrochloric acid.

\mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})

experiment $1 \quad \mathrm{CaCO}_{3}$ powder $+2.0 \mathrm{moldm}^{-3} \mathrm{HCl}$ at $35^{\circ} \mathrm{C}$
experiment $2 \mathrm{CaCO}_{3}$ powder $+2.0 \mathrm{moldm}^{-3} \mathrm{HCl}$ at $35^{\circ} \mathrm{C}$
experiment 3 large chips of $\mathrm{CaCO}_{3}+1.0 \mathrm{moldm}^{-3} \mathrm{HCl}$ at room temperature
experiment 4 large chips of $\mathrm{CaCO}_{3}+1.0 \mathrm{moldm}^{-3} \mathrm{HCl}$ at $35^{\circ} \mathrm{C}$

The student collects the $\mathrm{CO}_{2}(\mathrm{~g})$ and times how long it takes to produce the same volume of gas for each experiment.

What could be the correct times for the four experiments?

experiment 1 /s

experiment 2 /s

experiment 3 /s

experiment 4 /s

5

10

30

95

5

10

95

30

5

30

95

10

95

30

10

5

[Maximum number: 1]

An autocatalytic reaction is a reaction in which one of the products catalyses the reaction.
Which curve was obtained if the rate of reaction was plotted against time for an autocatalytic reaction?

A

B

C

D

[Maximum number: 1]

$\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ reacts with dilute HCl to give a pale yellow precipitate. If $1 \mathrm{~cm}^{3}$ of $0.1 \mathrm{moldm}^{-3} \mathrm{HCl}$ is added to $10 \mathrm{~cm}^{3}$ of $0.02 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ the precipitate forms slowly.

If the experiment is repeated with $1 \mathrm{~cm}^{3}$ of $0.1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{HCl}$ and $10 \mathrm{~cm}^{3}$ of $0.05 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ the precipitate forms more quickly.

Why is this?

A

The activation energy of the reaction is lower when $0.05 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ is used.

B

The collisions between reactant particles are more violent when $0.05 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ is used.

C

The reactant particles collide more frequently when $0.05 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ is used.

D

The reaction proceeds by a different pathway when $0.05 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$ is used.

[Maximum number: 1]

In the diagram, curve X was obtained by observing the decomposition of $100 \mathrm{~cm}^{3}$ of $1.0 \mathrm{~mol} \mathrm{dm}^{-3}$ hydrogen peroxide, catalysed by manganese(IV) oxide.

Which alteration to the original experimental conditions would produce curve Y ?

A

adding more manganese(IV) oxide

B

adding some $0.1 \mathrm{~mol} \mathrm{dm}^{-3}$ hydrogen peroxide

C

adding water

D

raising the temperature

[Maximum number: 1]

In the diagram, curve X was obtained by observing the decomposition of $100 \mathrm{~cm}^{3}$ of $1.0 \mathrm{~mol} \mathrm{dm}^{-3}$ hydrogen peroxide, catalysed by manganese(IV) oxide.

Which alteration to the original experimental conditions would produce curve Y ?

A

adding some $0.1 \mathrm{~mol} \mathrm{dm}^{-3}$ hydrogen peroxide

B

adding water

C

lowering the temperature

D

using less manganese(IV) oxide