Chemical Thermodynamics Question 209
Question: The heat of combustion of $ C{H_{4(g)}},,{C_{(graphite)}} $ and $ {H_{2(g)}} $ are $ 20,kcal,,-40,kcal $ and $ -10,kcal $ respectively. The heat of formation of methane is [EAMCET 1998]
Options:
A) $ -4.0,kcal $
B) $ +40,kcal $
C) $ -80,kcal $
D) $ +80,kcal $
Show Answer
Answer:
Correct Answer: C
Solution:
Given, (i) $ CH_4+2O_2\to CO_2+2H_2O $ , $ \Delta H=+20 $ kcal (ii) $ C+O_2\to CO_2 $ , $ \Delta H=-40kcal. $ (iii) $ H_2+\frac{1}{2}O_2\to H_2O $ , $ \Delta H=-10kcal. $ Aim: $ C+2H_2\to CH_4 $ (ii) + 2 × (iii) - (i) gives. $ \Delta H=-40+2,(-10)-(+,20)=-80, & ,kcal. $
