JAMB Chemistry 2020 Question 13

Question 13

Energy Changes

2CO_(g) + O_2(g) → 2CO_2(g)
In the above reaction, the standard heats of formation of CO_(g) and CO_2(g) are −297KJmol⁻¹ and −396KJmol⁻¹ respectively. The heat change of the reaction is

A.−99KJmol⁻¹
B.+198KJmol⁻¹
C.−198KJmol⁻¹
D.+683KJmol⁻¹

Show the answer and explanation

Answer: C (−198KJmol⁻¹)

Explanation

ΔH = Σ products − Σ reactants = 2(−396) − 2(−297) = −792 + 594 = −198 kJ mol⁻¹ (O₂ is an element, so its value is 0).