9701 MCQ Solution 10

Question 10: [Physical > Chemical Energetics]:

At 600°C oxides of nitrogen react with un-burnt hydrocarbons in a catalytic converter in a car exhaust. The equation using methane as representative of a hydrocarbon molecule would be as follows.

4NO + CH₄ à2N₂ + CO₂ + 2H₂O

Which statement is likely to be true about the energy change of this reaction?

A It is endothermic as heat energy is converted into chemical energy.

B It is exothermic as a high temperature is required.

C It is exothermic as the triple bond NO is broken.

D It is exothermic as the products have large negative enthalpy changes of formation.

Reference: Past Exam Paper – November 2002 Paper 1 Q10

Solution 10:

Answer: D.

A cannot be answer because conversion of energy is not endothermic
B cannot be an answer because exothermic reactions do not require a high temperature to start unlike endothermic reactions because exothermic reactions have a smaller activation energy compared to endothermic reactions . Exothermic reactions have s smaller activation energy and therefore do not require high temperature and therefore exothermic reactions occur more readily and at a faster rate than endothermic reactions
C cannot be answer because breaking of a bond is endothermic