Chemical Thermodynamics Question 227
Question: For the allotropic change represented by equation $ C(diamond)\to C(graphite) $ ; the enthalpy change is $ \Delta H=-1.89,kJ $ . If $ 6,g $ of diamond and $ 6,g $ of graphite are separately burnt to yield carbon dioxide, the heat liberated in the first case is [KCET 1988; DPMT 2000]
Options:
A) Less than in the second case by $ 1.89,kJ $
B) More than in the second case by $ 1.89,kJ $
C) Less than in the second case by $ 11.34,kJ $
D) More than in the second case by $ 0.945,kJ $
Show Answer
Answer:
Correct Answer: D
Solution:
$ {C_{(graphite)}}\to {C_{(diamond)}},\Delta H=1.9,kJ $
$ {C_{(graphite)}}+O_2\to CO_2,\Delta H=-\Delta H_1 $
$ {C_{(diamond)}}+O_2\to CO_2,,\Delta H=-\Delta H_2 $
$ (,-\Delta H_1)-(,-\Delta H_2)=1.9,kJ $ or $ \Delta H_2=\Delta H_1+1.9 $ For combustion of $ 6g,\Delta H_2>\Delta H_1 $ by $ 1.9/2=0.95,kJ. $
