Question 1

Marks: 1

The first stage in the industrial production of nitric acid from ammonia can be represented by the following equation.

4NH₃(g) + 5O₂(g) ⇌ 4NO(g) + 6H₂O(g)

Using the following standard enthalpy change of formation data, what is the value of the standard enthalpy change $∆ H^{⦵}$ for this reaction?

Compound	$∆ H_{f}^{⦵}$ /kJ mol^{– 1}
NH₃ (g)	-46.1
NO (g)	+90.3
H₂O (g)	-241.8

$(4 \times (- 46.1)) + ((4 \times 90.3) + (6 \times (- 241.8))$
$((4 \times 90.3) + (6 \times (- 241.8)) - (4 \times (- 46.1))$
$(4 \times (- 46.1)) - ((4 \times 90.3) + (6 \times (- 241.8)))$
$(- 46.1) - (90.3) + (- 241.8)$

Question 2

Marks: 1

Titanium occurs naturally as the mineral rutile, TiO₂. One possible method of extraction of titanium is to reduce the rutile by heating with carbon.

TiO₂(s) + 2C(s) → Ti(s) + 2CO(g)

The standard enthalpy changes of formation of TiO₂(s) and CO(g) are –890 kJ mol^-1 and –110.5 kJ mol^-1 respectively.

What is the standard enthalpy change of the extraction of titanium?

+ 669 kJ mol^–1
+ 779.5 kJ mol^–1
– 779.5 kJ mol^–1
– 669 kJ mol^–1

Question 3

Marks: 1

The combustion of ethanol (C₂H₅OH) is increasingly being used to fuel cars. The combustion reaction is shown below

C₂H₅OH(l) + 3O₂ (g) → 2CO₂(g) + 3H₂O(l)

The standard enthalpy change of formation of carbon dioxide is a kJ mol^–1.

The standard enthalpy change of formation of water is b kJ mol^–1.

The standard enthalpy change of formation of ethanol is c kJ mol^–1.

What is the standard enthalpy change of combustion for ethanol?

2a + 3b + c
2a + 3b − c
−2a − 3b + c
−2a − 3b −c

Question 4

Marks: 1

Propanone has the molecular formula C₃H₆O. Use the following information to calculate the enthalpy change for the formation of propanone?

The enthalpy change of combustion of carbon is x kJ mol ^-1

The enthalpy change of combustion of hydrogen is y kJ mol ^-1

The enthalpy change of combustion of propanone is z kJ mol ^-1

x + y - z
3x + 3y - z
z - 3x + 3y
3x + 3y + z

Question 5

Marks: 1

Combustion of ethene proceeds via the reaction shown in the Hess cycle diagram. q5_5-2_ib_sl_medium_mcq

What are the correct elements missing from the Hess cycle?

2C (g) + 2H₂ (g) + 3O₂ (g)
C (s) + H₂ (g) + O₂ (g)
2C (s) + 2H₂ (g) + 3O₂ (g)
C₂ (s) + 2H₂ (g) + 3O₂ (g)

Question 6

Marks: 1

Combustion of propene proceeds via the reaction shown in the Hess cycle diagram. q6_5-2_ib_sl_medium_mcq

Which are the correct labels for the enthalpies shown in the Hess cycle?

	P	Q	R	S
A	ΔH^Ө_c	ΔH^Ө_r	ΔH^Ө_c	ΔH^Ө_c
B	ΔH^Ө_c	ΔH^Ө_f	ΔH^Ө_r	ΔH^Ө_r
C	ΔH^Ө_c	ΔH^Ө_f	ΔH^Ө_c	ΔH^Ө_f
D	ΔH^Ө_r	ΔH^Ө_r	ΔH^Ө_f	ΔH^Ө_f

Question 7

Marks: 1

Hess’s Law can be used to calculate the enthalpy change for reactions that are difficult to measure experimentally, such as the conversion of graphite to diamond.

Which enthalpy data could be used to calculate the enthalpy change for the conversion of graphite to diamond?

Enthalpy of reaction
Enthalpy of combustion
Enthalpy of formation

I and II only
I and III only
II and III only
I, II and III

Question 8

Marks: 1

A basic definition of Hess’s Law states that the overall enthalpy change for a reaction is the same independent of the route taken.

The addition of which of the following statements makes the definition of Hess’s Law more complete?

Providing that the reactants are the same
Providing that the products are the same
Providing that the conditions at the start and the end of the reaction are the same

I and II only
I and III only
II and III only
I, II and III

Question 9

Marks: 1

The hydration enthalpy of anhydrous copper(II) sulfate cannot be measured directly. It can be found indirectly by determining the solution enthalpies of anhydrous and hydrated copper(II) sulfate. q9_5-2_mcq_medium_ib-chemistry-sl

Which are the correct labels for the enthalpies shown in the Hess cycle?

	1	2	3
A	ΔH^Ө_sol	ΔH^Ө_hyd	ΔH^Ө_hyd
B	ΔH^Ө_r	ΔH^Ө_hyd	ΔH^Ө_hyd
C	ΔH^Ө_hyd	ΔH^Ө_sol	ΔH^Ө_hyd
D	ΔH^Ө_r	ΔH^Ө_sol	ΔH^Ө_sol

Question 10

Marks: 1

The hydration enthalpy of anhydrous copper(II) sulfate, labelled as ΔH_exp, cannot be measured directly. It can be found indirectly by determining the solution enthalpies of anhydrous and hydrated copper(II) sulfate.

q10_5-2_mcq_medium_ib-chemistry-sl

Which of the following statements correctly explains why the value for ΔH_exp for this reaction cannot be measured directly?

Measuring the temperature change in a solid is difficult
The reaction is very slow
The reaction has high energy requirements
The reaction is endothermic

DP IB Chemistry: HL

Topic Questions

5.2 Hess's Law

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

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