Chemical Thermodynamics Question 292
Question: Heats of combustion $ (\Delta H^{o}) $ for $ C(s),,H_2(g) $ and $ CH_4(g) $ are $ -94,,-68 $ and $ -213,kcal/mol. $ respectively. The value of $ \Delta H^{o} $ for the reaction, $ C(s)+2H_2(g),\to ,CH_4(g) $ is [CBSE PMT 2002]
Options:
A) - 85 kcal
B) - 111 kcal
C) - 17 kcal
D) - 170 kcal
Show Answer
Answer:
Correct Answer: C
Solution:
$ C_s+2H _{2g} \to CH _{4g} $ -..(i)
$ {C_{(s)}}+{O_{2(g)}}\to C{O_{2(g)}},\Delta H=-94,kcal,mo{{l}^{-1}} $ -..(ii) $ {H_{2(g)}}+\frac{1}{2}{O_{2(g)}}\to H_2{O_{(l)}},\Delta H=-68,kcal,mo{{l}^{-1}} $ - (iii) $ CH_4+3{/_2}O_2\to CO_2+2H_2O $
$ \Delta H=-213,kcal,mo{{l}^{-1}} $ - (iv) to obtain equation (i) operate-(ii) + 2 × (iii) - (iv).
