Chemical Thermodynamics Question 232
Question: If enthalpies of formation of $ C_2H_4(g),,CO_2(g) $ and $ H_2O(l) $ at $ 25^{o}C $ and $ 1,atm $ pressure be 52, - 394 and $ -286,kJ,mo{{l}^{-1}} $ respectively, the enthalpy of combustion of $ C_2H_4(g) $ will be [CBSE PMT 1995; AIIMS 1998; Pb. PMT 1999]
Options:
A) $ +1412,kJ,mo{{l}^{-1}} $
B) $ -1412,kJ,mo{{l}^{-1}} $
C) $ +141.2,kJ,mo{{l}^{-1}} $
D) $ -141.2,kJ,mo{{l}^{-1}} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ C_2H_4+3O_2\to 2CO_2+2H_2O $
$ \Delta {H_{reaction}}=[2\times \Delta H_{f}^{o}(CO_2)+2\times \Delta H_{f}^{o},(H_2O)] $
$ -[\Delta H_{f}^{o},(C_2H_4)+,3\times \Delta H_{f}^{o},(O_2)] $
$ =[,2,(,-394)+2,(,-286)]-[52+0]=-1412,kJ $ .
