Question

Two reactions are given below :
$C_{\left(graphite\right)} + O_{2\left(g\right)} \to CO_{2\left(g\right)}; \Delta H = - 393.7 \,kj$ ;
$C_{\left(diamond\right)} ^{ }\to C_{\left(graphite\right)}; \Delta H = -2.1 \,kj$
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 1

Answer: (A)

$C_{\left(diamond\right)} \to O_{2\left(g\right)} \to CO_{2\left(g\right)}$
$= -393.7 + \left(-2.1\right) = -395.8 \,kj$
$12\, g$ diamond gives $395.8\, kj$.
$800 \,kj$ will be given by $\frac{12}{395.8}\times800 = 24.25\,g$