1.This question is about the manufacture of

ammonia. The equation for the formation of

ammonia is N2(g) + 3H2(g) → 2NH3(g)

The standard enthalpy of formation of ammonia

is –46.2 kJ mol–1.

(a)(i) By reference to ammonia, define the term

standard enthalpy of formation.

(ii) Use the standard enthalpy of formation of

ammonia to calculate the enthalpy change for the

reaction shown in the equation above.

(iii) Use the bond enthalpies below to calculate

another value for the enthalpy change for the

reaction shown in the equation above. [Bond

enthalpies / kJ mol–1: N=N = +944; H—H = +436;

N—H = +388]

(iv) Suggest why the two values obtained for the

enthalpy change that you have calculated in

parts a) (ii) and iii are different, even though the

data in both cases are measured under standard

conditions.

(b)Draw an energy level diagram for the

formation reaction of ammonia.

2. Some standard enthalpy of combustion values are given below.

(i) Define standard enthalpy change of combustion of propane.(ii) Write a thermochemical equation for the standard enthalpy change of combustion of propane.

Substance ∆HCӨ/kJ mol─1

C (graphite) –393.5

H2(g) –285.8

propane C3H8(g) –2060.0

(iii) Use the data to calculate the standard

enthalpy change of propane. Draw a Hess’s Law

cycle as part of your answer. 3. Calculate the enthalpy of combustion of ane

by drawing an energy cycle and using the

following enthalpy of formation data:

Substance ∆Hf/kJ mol─1

methane ─75

Carbon dioxide ─394

water ─286

Relative abundance %

69 27 4

m/z 58 60 62

4. (a) Define the term relative atomic mass of an

element.

(b) A sample of nickel was analysed in a mass

spectrometer. Three peaks were observed with the

properties shown in the following table.

(i) Calculate the relative atomic mass of this

sample of nickel.

(ii) Identify species which was responsible for the

peak at m/z = 58.

(iii) What is the function of the electron gun and

the magnet in the mass spectrometer?