Chemistry - Thermochemistry Question with Solution | TestHub
When carbon is burnt in a limited supply of oxygen the product is CO, and with excess O2 it is CO2. The enthalpies of formation of CO(g) and CO2(g) are -26 and -94 kcal/mol, respectively. In which of the following cases will the heat evolved be maximum?
Options:
Answer:
Solution:
(a) When carbon (C) is in excess, 2 mol of O₂ yields 4 mol of CO. The heat produced is 4 × 26 = 104 kcal.
(b) When O₂ is sufficient for CO₂ formation, 2.5 mol of O₂ burns 2.5 mol of C to form CO₂. The heat produced is 2.5 × 94 = 235 kcal.
(c) When 1 mol of C reacts with 1 mol of O₂, 1 mol of CO₂ is formed. The heat produced is 94 kcal.
(d) When 2 mol of C reacts with 1.5 mol of O₂, 1.5 mol of CO₂ is formed. The heat produced is 1.5 × 94 = 141 kcal.
The maximum heat produced occurs in case (b).
