R1.2 Energy cycles in reactions questions for IB Chemistry

144 questions on Energy cycles in reactions, 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 R1 What drives chemical reactions?
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	30	27	57
Paper 1B	7	10	17
Paper 2	33	37	70
Every paper	70	74	144

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-00184Paper 1A · HL only · 1 mark

The following data relate to potassium chloride.

Process	ΔH / kJ mol⁻¹
Enthalpy of atomization of potassium	+89
First ionization energy of potassium	+419
Cl–Cl bond enthalpy	+242
First electron affinity of chlorine	−349
Enthalpy of formation of KCl(s)	−437

What is the lattice enthalpy of potassium chloride, in kJ mol⁻¹?

A
−157
B
+717
C
+838
D
+1415

The answer and whyCheck this one with a free account

Question 2 · CHEM-00810Paper 1B · 12 marks

The enthalpy change for the hydration of anhydrous copper(II) sulfate cannot be measured directly.

C u S O_{4} (s) + 5 H_{2} O (l) \to C u S O_{4} \cdot 5 H_{2} O (s) Δ H_{hyd}

A student determined it indirectly from two experiments. In each, the solid was added to 50.0 cm³ of water in a polystyrene cup, stirred, and the highest or lowest temperature was recorded.

Experiment 1: 4.00 g of anhydrous $C u S O_{4}$ dissolved, giving $Δ H_{1}$ .
Experiment 2: 6.25 g of $C u S O_{4} \cdot 5 H_{2} O$ dissolved, giving $Δ H_{2}$ .

	Experiment 1	Experiment 2
Mass of solid / g ± 0.01 g	4.00	6.25
Initial temperature / °C ± 0.1 °C	21.3	21.5
Final temperature / °C ± 0.1 °C	28.7	20.2

Assume the specific heat capacity of the solution is that of water (section 2 of the data booklet) and that only the 50.0 g of water is heated or cooled.

(a)
Suggest why $Δ H_{hyd}$ cannot be measured directly in a calorimeter.
1 mark
(b)
Calculate $Δ H_{1}$ , in kJ mol⁻¹.
3 marks
(c)
Calculate $Δ H_{2}$ , in kJ mol⁻¹.
2 marks
(d)
Construct a Hess's law cycle linking $Δ H_{hyd}$ , $Δ H_{1}$ and $Δ H_{2}$ , and use it to determine $Δ H_{hyd}$ , in kJ mol⁻¹.
2 marks
(e)
The literature value of $Δ H_{hyd}$ is −78.2 kJ mol⁻¹. Calculate the percentage error in the student's value.
1 mark
(f)
Calculate the percentage uncertainty in the temperature change in Experiment 2 and state its effect on the reliability of $Δ H_{hyd}$ .
2 marks
(g)
Suggest one modification to Experiment 2 that would reduce the percentage uncertainty in its temperature change.
1 mark

The markschemeCheck this one with a free account

Question 3 · CHEM-00289Paper 2 · 8 marks

Carbon monoxide, CO, is a toxic gas formed by the incomplete combustion of fuels. In a catalytic converter it is oxidized to carbon dioxide.

2 C O (g) + O_{2} (g) \to 2 C O_{2} (g)

(a)
Draw the Lewis (electron dot) formula of carbon monoxide and identify the coordination bond in it.
2 marks
(b)(i)
Using section 11 of the data booklet, list the carbon–oxygen bonds in CO, CO₂ and CH₃OH in order of increasing bond length.
1 mark
(b)(ii)
Outline the reason for the order in (b)(i).
1 mark
(c)
Calculate the enthalpy change, in kJ, for the oxidation of carbon monoxide shown in the equation, using section 12 of the data booklet.
3 marks
(d)
Using section 9 of the data booklet, state, giving a reason, whether a molecule of carbon monoxide is polar.
1 mark

The markschemeCheck this one with a free account

Question 4 · CHEM-00322Paper 1A · HL only · 1 mark

The standard enthalpies of combustion of carbon (graphite), hydrogen and ethanol are given.

Substance	ΔH_c^⦵ / kJ mol⁻¹
C(s, graphite)	−394
H₂(g)	−286
C₂H₅OH(l)	−1367

What is the standard enthalpy of formation of ethanol, in kJ mol⁻¹?

2 C (s) + 3 H_{2} (g) + \frac{1}{2} O_{2} (g) \to C_{2} H_{5} O H (l)

A
−3013
B
−279
C
+279
D
+687

The answer and whyCheck this one with a free account

Question 5 · CHEM-00811Paper 1B · 10 marks

The enthalpy change for the reaction $M g (s) + \frac{1}{2} O_{2} (g) \to M g O (s)$ was determined indirectly. A student carried out two experiments, each with 50.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid (an excess) in a polystyrene cup with a lid.

Reaction 1: $M g (s) + 2 H C l (a q) \to M g C l_{2} (a q) + H_{2} (g)$ $Δ H_{1}$
Reaction 2: $M g O (s) + 2 H C l (a q) \to M g C l_{2} (a q) + H_{2} O (l)$ $Δ H_{2}$
Reaction 3: $H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l)$ $Δ H_{3} = - 286 {kJ mol}^{- 1}$

	Reaction 1	Reaction 2
Solid added	Mg ribbon	MgO powder
Mass of solid / g ± 0.001 g	0.240	0.400
Temperature rise / °C ± 0.2 °C	20.6	6.6

(a)
Show that hydrochloric acid is in excess in Reaction 1.
1 mark
(b)
Calculate $Δ H_{1}$ , in kJ mol⁻¹. Assume the solution has the density and specific heat capacity of water.
2 marks
(c)
Calculate $Δ H_{2}$ , in kJ mol⁻¹.
1 mark
(d)
Determine the enthalpy change, in kJ mol⁻¹, for the formation of magnesium oxide from magnesium and oxygen.
2 marks
(e)
The literature value is −602 kJ mol⁻¹. Calculate the percentage error.
1 mark
(f)
Outline why the magnesium ribbon is cleaned with sandpaper before it is weighed, and the effect on $Δ H_{1}$ if this step were left out.
2 marks
(g)
Suggest one source of systematic error, other than heat loss, in Reaction 1.
1 mark

The markschemeCheck this one with a free account

Question 6 · CHEM-00294Paper 2 · 8 marks

Phosphorus trichloride, PCl₃, is a colourless liquid used to make pesticides. Nitrogen trichloride, NCl₃, is a yellow oil that can decompose explosively.

(a)
Draw the Lewis (electron dot) formula of PCl₃.
1 mark
(b)
Deduce the molecular geometry of PCl₃ and predict its Cl–P–Cl bond angle.
2 marks
(c)
Using section 9 of the data booklet, compare the polarity of the N–Cl bond with that of the P–Cl bond. Include the direction of each bond dipole.
2 marks
(d)
Calculate the enthalpy change, in kJ, for the decomposition of gaseous nitrogen trichloride, using section 12 of the data booklet.
$2 N C l_{3} (g) \to N_{2} (g) + 3 C l_{2} (g)$
2 marks
(e)
Suggest, with reference to bonding, why the decomposition in (d) releases so much energy.
1 mark

The markschemeCheck this one with a free account

Practice all 144 in Augment

Free with an account. Every question has its markscheme, and Augment keeps the ones you got wrong so you can come back to them.

Start free Log in

The notes on R1.2 Energy cycles in reactions

Check your answers in Augment

A free account opens all 144 questions on Energy cycles in reactions with their markschemes, and keeps a record of what you have marked.

Start free

Questions by paper and level

Questions to try

Practice all 144 in Augment

More questions in What drives chemical reactions?

Check your answers in Augment