Edexcel IGCSE Chemistry 3 Physical Chemistry Questions

Practise energy changes, reaction rates and equilibrium ideas through calculations, graphs, diagrams and explanations using particle models.

Covered syllabus points

(a) Energetics (b) Rates of reaction (c) Reversible reactions and equilibria

[Maximum number: 1]

The teacher demonstrates the reaction between aluminium and iron(III) oxide.

Figure for Question 1 — Edexcel IGCSE Chemistry

The teacher ignites the magnesium fuse. A very exothermic reaction then occurs between aluminium powder and iron(III) oxide.

The products of the reaction are iron and aluminium oxide.

State what is meant by the term exothermic.

[Maximum number: 9]

Dilute hydrochloric acid reacts with a solution of sodium thiosulfate $\left(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\right)$ to form a precipitate.

The equation for the reaction is

\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow 2 \mathrm{NaCl}(\mathrm{aq})+\mathrm{S}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{SO}_{2}(\mathrm{~g})

(a)

The reaction is often used to investigate rates of reaction.

The diagram shows the apparatus a student uses to investigate the effect of temperature on the rate of the reaction.

Figure for Question (a) — Edexcel IGCSE Chemistry

This is the student's method.
- pour $50 \mathrm{~cm}^{3}$ of cold sodium thiosulfate solution into a conical flask and heat it to $20^{\circ} \mathrm{C}$
- draw a cross ( X ) on a piece of paper and place it under the flask
- add $5 \mathrm{~cm}^{3}$ of dilute hydrochloric acid to the flask
- look at the cross from above and record the time taken until the cross cannot be seen

The student repeats the experiment four times, using sodium thiosulfate solution at a different temperature each time.

He keeps the volumes of sodium thiosulfate solution and hydrochloric acid constant in each experiment.

Give two other factors that the student should keep constant.

1
2

[ 2 ]

(b)

The table shows the student's results.

Table for Question (b) — Edexcel IGCSE Chemistry

The highest temperature the student uses is 60 °C because he thinks the results might not be as accurate at temperatures higher than 60 °C.

Suggest a reason why the results might not be as accurate at temperatures higher than 60 °C.

[ 1 ]

(c)

Calculate the time that it would take for the cross not to be seen at 45 °C.

time = ................................ s

[ 2 ]

(d)

Describe the relationship between rate of reaction and temperature shown by the graph.

[ 1 ]

(e)

Explain, in terms of particle collision theory, the effect that increasing the temperature has on the rate of a reaction.

[ 3 ]

[Maximum number: 2]

(a)

Methanoic acid also reacts with propanol to form an ester.

The equation for the reaction is

\mathrm{HCOOH}+\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} \rightleftharpoons \mathrm{HCOOC}_{3} \mathrm{H}_{7}+\mathrm{H}_{2} \mathrm{O}

[ 2 ]

(i)

State what is meant by the ⇌ symbol.

[ 1 ]

(ii)

When this reaction occurs in a sealed container, the reaction can reach dynamic equilibrium.

Give one characteristic of a reaction at dynamic equilibrium.

[ 1 ]

[Maximum number: 9]

A student investigates the reaction between zinc and copper(II) sulfate solution.
This is the equation for the reaction.

\mathrm{Zn}(\mathrm{~s})+\mathrm{CuSO}_{4}(\mathrm{aq}) \rightarrow \mathrm{ZnSO}_{4}(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})

This is the student's method.
Step 1 add $25.0 \mathrm{~cm}^{3}$ of copper(II) sulfate solution to a glass beaker
Step 2 record the temperature of the solution
Step 3 add between 5 g and 6 g of zinc powder (an excess) and stir the mixture
Step 4 record the highest temperature reached

(a)

Explain an improvement to step 1 to produce a more accurate temperature rise.

[ 2 ]

(b)

The table shows the student's results.

Calculate the heat energy change ( Q ) in joules (J).
[for the solution, $\mathrm{c}=4.2 \mathrm{~J} / \mathrm{g} /{ }^{\circ} \mathrm{C}$ ]
[mass of $1.0 \mathrm{~cm}^{3}$ of solution $=1.0 \mathrm{~g}$ ]

Q=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . .

[ 3 ]

$\mathrm{M} 1 \Delta \mathrm{~T}=30.1\left({ }^{\circ} \mathrm{C}\right)$

M2 $25 \times 4.2 \times 30.1$

ALLOW ecf from M1

M3 3160.5(J)

ALLOW any number of
significant figures from
2

(c)

The student repeats the experiment and calculates Q as 3800 J.

The solution used contains 6.38 g of copper(II) sulfate.
Calculate the molar enthalpy change, $\Delta H$ , in kJ / mol.
Include a sign in your answer.
[for $\mathrm{CuSO}_{4}, M_{\mathrm{r}}=159.5$ ]

[ 4 ]

- moles of $\ce{CuSO4}$ = 6.38 / 159.5 = 0.04 mol
- 3800 / 0.04 = 95000
- divide by 1000 = 95 kJ
- molar enthalpy change = -95 kJ/mol

Allow:
- ECF from moles
- ECF from energy per mole

Marking guidance:
- Correct answer -95 scores 4.
- ECF -79 scores 3 if using the energy change from 10(b)(i).

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question 3

Question (a)

Question (i)

Question (ii)

Question 4

Question (a)

Question (b)

Question (c)