GCSE / O Levels Chemistry

Under certain conditions nitrogen reacts with oxygen to form N20.
2N2(g) + O2(g)= 2N20(g)
The energy profile diagram for this reaction is shown.
energy
2N,0(g)
+447 kJ/mol
+164 kJ/mol
2N,(g) + 0,(g)
progress of reaction
What is the activation energy for the reverse reaction?
A -447 kJ/mol
B
-283 kJ/mol
C +141.5 kJ/mol
D +283 kJ/mol


Choice D is correct because:

Since the forward reaction is endothermic, the enthalpy change for the reaction will be: ΔH = +164 kJ/mol

The reverse reaction will therefore be exothermic.

The enthalpy change for the reverse reaction will be: ΔH = -164 kJ/mol

The activation energy is always positive, irrespective of whether the reaction proceeds forward or backward.

To calculate the activation energy for the reverse reaction: +447 kJ/mol + (-164 kJ/mol) = +283 kJ/mol

Choices A, B and C are incorrect because they do not state the correct value of the activation energy for the reverse reaction.

Reaction Pathway diagrams | 2017 - O/N - 5070/11 | Q17