R2.3 How far? The extent of chemical change questions for IB Chemistry

157 questions on How far? The extent of chemical change, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Chemistry
Part of R2 How much, how fast and how far?
SL and HL

Questions by paper and level

SL and HL questions are for students at either level. HL only questions cover what only HL students study.

Paper	SL and HL	HL only	All
Paper 1A	32	33	65
Paper 1B	8	11	19
Paper 2	34	39	73
Every paper	74	83	157

Counted on 10 November 2026

Questions to try

Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · CHEM-01015Paper 1A · HL only · 1 mark

Which statement is correct for a reaction mixture that has reached equilibrium at constant temperature and pressure?

A
$Δ G^{⊖} = 0$
B
$Δ G = 0$
C
$K = 0$
D
$Δ G = Δ G^{⊖}$

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Question 2 · CHEM-01056Paper 1B · 10 marks

A student modelled ocean acidification. Carbon dioxide was bubbled at a constant rate into 200 cm³ of seawater and, separately, into 200 cm³ of deionized water. The pH was recorded with a data logger.

Time / min	0	1	2	3	4	5	6	8	10
pH of deionized water ± 0.1	6.9	5.2	4.8	4.6	4.5	4.4	4.3	4.2	4.2
pH of seawater ± 0.1	8.2	7.6	7.2	6.9	6.6	6.4	6.2	6.0	5.9

A fragment of shell made of calcium carbonate was then placed in the acidified seawater. Its mass fell from 2.415 g to 2.302 g after seven days.

(a)
State the dependent variable in the first part of the experiment.
1 mark
(b)
Write two equations to show how dissolving carbon dioxide lowers the pH of water.
2 marks
(c)
Compare the changes in pH of the two samples.
2 marks
(d)
Calculate the factor by which the hydrogen ion concentration of the seawater increased over the 10 minutes.
1 mark
(e)
Suggest why the pH of seawater falls more slowly than that of deionized water.
2 marks
(f)
Calculate the percentage loss in mass of the shell.
1 mark
(g)
Suggest why this model may overestimate the effect of ocean acidification on shells.
1 mark

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Question 3 · CHEM-00439Paper 2 · 8 marks

The concentration of carbon dioxide in the atmosphere has risen from about 280 ppm before industrialization to over 420 ppm today. Over the same period, the average pH of surface seawater has fallen from about 8.2 to 8.1.

(a)
Write the equation for the reaction of carbon dioxide with water.
1 mark
(b)
Write an equation to show how the product in (a) releases hydrogen ions.
1 mark
(c)
Calculate the factor by which the hydrogen ion concentration of surface seawater has increased.
2 marks
(d)
Corals and shellfish build their skeletons and shells from calcium carbonate.
$C a^{2 +} (a q) + C O_{3}^{2 -} (a q) ⇌ C a C O_{3} (s)$
Explain, using an equation, why increasing hydrogen ion concentration makes it harder for these organisms to form shells.
3 marks
(e)
Outline why carbon dioxide is described as an acidic oxide.
1 mark

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Question 4 · CHEM-01019Paper 1A · HL only · 1 mark

For a reaction at 298 K, $Δ G^{⊖} = - 11.4 {kJ mol}^{- 1}$ . What is the value of the equilibrium constant, $K$ , at 298 K?

A
0.010
B
1.00
C
4.60
D
100

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Question 5 · CHEM-01899Paper 1B · HL only · 12 marks

A student determined $Δ H^{⊖}$ and $Δ S^{⊖}$ for dissolving potassium nitrate from its solubility at different temperatures.

K N O_{3} (s) ⇌ K^{+} (a q) + N O_{3}^{-} (a q) K = [K^{+}] [N O_{3}^{-}] = s^{2}

where $s$ is the concentration of the saturated solution in mol dm⁻³.

Method:

A known mass of $K N O_{3}$ was added to 10.0 cm³ of water in a graduated boiling tube.
The tube was heated in a water bath until all the solid dissolved, and the total volume of solution was read.
The tube was removed and the solution stirred with a thermometer as it cooled. The temperature at which crystals first appeared was recorded.

Mass of KNO₃ / g ± 0.01 g	Volume of solution / cm³ ± 0.2 cm³	Crystallization temperature / °C ± 0.5 °C	$s$ / mol dm⁻³	$\ln K$	$\frac{1}{T}$ / $10^{- 3}$ K⁻¹
4.00	11.6	28.0	3.41	2.45	3.321
5.00	12.0	36.5	4.12	2.83	3.229
6.00	12.4	41.5
7.00	12.8	47.0	5.41	3.38	3.124
8.00	13.2	51.5	5.99	3.58	3.080

Combining $Δ G^{⊖} = - R T \ln K$ with $Δ G^{⊖} = Δ H^{⊖} - T Δ S^{⊖}$ gives:

\ln K = - \frac{Δ H^{⊖}}{R} (\frac{1}{T}) + \frac{Δ S^{⊖}}{R}

The graph shows all five results with a line of best fit.

best fit

ln K (y-axis) against 1/T in 10⁻³ K⁻¹ (x-axis) for dissolving KNO₃

(a)
Identify the independent and the dependent variable in this experiment.
1 mark
(b)
Explain why the temperature at which crystals first appear is used.
1 mark
(c)
Calculate the missing values of $s$ , $\ln K$ and $\frac{1}{T}$ for the 6.00 g sample. $M (K N O_{3}) = 101.11 {g mol}^{- 1}$ .
2 marks
(d)
Calculate the percentage uncertainty in $K$ for the 4.00 g sample, using section 23 of the data booklet.
2 marks
(e)
Determine $Δ H^{⊖}$ , in kJ mol⁻¹, for dissolving potassium nitrate, using the gradient of the line of best fit.
2 marks
(f)
Calculate $Δ G^{⊖}$ at 320.1 K, using the value of $\ln K$ for the 7.00 g sample, and hence determine $Δ S^{⊖}$ , in J K⁻¹ mol⁻¹.
2 marks
(g)
Explain the sign of $Δ S^{⊖}$ for dissolving potassium nitrate.
1 mark
(h)
Suggest one source of random error in the method and an improvement to reduce its effect.
1 mark

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Question 6 · CHEM-00763Paper 2 · HL only · 9 marks

A solution of cobalt(II) chloride in water is pink because it contains $[C o (H_{2} O)_{6}]^{2 +}$ . When concentrated hydrochloric acid is added, the solution turns blue.

[C o (H_{2} O)_{6}]^{2 +} (a q) + 4 C l^{-} (a q) ⇌ [C o C l_{4}]^{2 -} (a q) + 6 H_{2} O (l)

Complex	Wavelength of maximum absorption / nm
$[C o (H_{2} O)_{6}]^{2 +}$	515
$[C o C l_{4}]^{2 -}$	625

(a)
Deduce the condensed electron configuration of the cobalt ion in these complexes.
1 mark
(b)
Deduce the oxidation state of cobalt in $[C o C l_{4}]^{2 -}$ .
1 mark
(c)
Using section 15 of the data booklet, deduce the colour of light absorbed by $[C o C l_{4}]^{2 -}$ and the colour expected to be observed.
2 marks
(d)
Calculate the energy, in J, of one photon of light of wavelength 625 nm. Use sections 1 and 2 of the data booklet.
2 marks
(e)
Suggest why the two complexes have different colours.
2 marks
(f)
Deduce, giving a reason, in which complex the energy gap between the split d orbitals is larger.
1 mark

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