Chemistry - Thermochemistry Question with Solution | TestHub
ΔH of which of the following reaction(s) may be directly taken as enthalpy of combustion of the concerned substance? (one or more than one correct)
Options:(select one or more)
Answer:
Solution:
The enthalpy of combustion is defined as the heat change that occurs when exactly 1 mole of a substance completely burns in excess O₂ to form stable oxides such as CO₂(g) and H₂O(l).
Let's analyze the given options:
(a) 1 mole of C (graphite) reacts to produce CO₂. This reaction represents the complete combustion of carbon.
(b) This reaction involves the combustion of 2 moles of ethane, meaning the Δ H value would be twice the molar enthalpy of combustion.
(c) This reaction produces CO, indicating incomplete combustion.
(d) This reaction is a formation reaction, not a combustion reaction.
Based on these analyses, only option (a) qualifies as an enthalpy of combustion. The answer is (a).
