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Q.
The heat of combustion of carbon to $CO_2$ is $- 393.5 \, kJ/mol$. The heat released upon formation of 35.2 g of $CO_2$ from carbon and oxygen gas is:
AIPMTAIPMT 2015Thermodynamics
Solution:
Formation of $CO_2$ from carbon and dioxygen gas can be represented as
$C(s) + O_{2(g)} \rightarrow CO_{2(g)} ; \Delta_fH = - 393.5 \; kJ \; mol^{-1}$
(1 mole = 44 g)
Heat released on formation of 44 g $CO_2$
$ = -393.5 \; kJ \; mol^{-1}$
$ = \frac{-393.5 \; kJ \; mol^{-1}}{44g} \times 35.2 g $
$ = - 315 \; kJ$