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. $



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