JAMB Chemistry 2003 Question 28

Question 28

Energy Changes

CO_(g) + H₂O_(g) → CO_2(g) + H_2(g)
From the reaction above, calculate the standard heat change if the standard enthalpies of formation of CO_2(g), H₂O_(g) and CO_(g) in kJ mol^-1 are –394, –242 and –110 respectively.

A.–262 kJ mol^-1
B.–42 kJ mol^-1
C.+42 kJ mol^-1
D.+262 kJ mol^-1

Show the answer and explanation

Answer: B (–42 kJ mol^-1)

Explanation

ΔH = (products) – (reactants) = (–394 + 0) – (–110 + –242) = –394 + 352 = –42 kJ mol^-1.