Question
Two reactions are given below :
$$\eqalign{
& {C_{{\text{(graphite)}}}} + {O_{2\left( g \right)}} \to C{O_{2\left( g \right)}};\Delta H = - 393.7\,kJ; \cr
& {C_{{\text{(diamond)}}}} \to {C_{{\text{(graphite)}}}};\Delta H = - 2.1\,kJ \cr} $$
What quantity of diamond will give 800$$\,kJ$$ of heat on burning ?
A.
24.25$$\,g$$
B.
15.24$$\,g$$
C.
2$$\,g$$
D.
12.12$$\,g$$
Answer :
24.25$$\,g$$
Solution :
$$\eqalign{
& {C_{{\text{(diarmond)}}}} + {O_{2\left( g \right)}} \to C{O_{2\left( g \right)}} \cr
& \Delta H = - 393.7 + \left( { - 2.1} \right) = - 395.8\,kJ \cr
& 12\,g\,\,{\text{diamond gives}}\,\,395.8\,kJ. \cr
& 800\,kJ\,\,{\text{will be given by}}\,\,\frac{{12}}{{395.8}} \times 800 = 24.25\,g \cr} $$