# Is this reaction endothermic or exothermic? Gas burning in a Bunsen burner: C_2H_6(g) + 3.5O_2(g) -> 2CO_2(g) + 3H2O(g) + 2855kJ

Dec 11, 2016

Clearly, the reaction is $\text{exothermic}$.

#### Explanation:

You are burning ethane; normally, the gas supplied to homes and labs is methane, $C {H}_{4}$.

$C {H}_{4} \left(g\right) + 2 {O}_{2} \left(g\right) \rightarrow C {O}_{2} \left(g\right) + 2 {H}_{2} O \left(g\right)$

The stability of the $C = O$ and $O - H$ bonds means that energy is released upon their formation, and the reaction is $\text{exothermic}$. Most combustion reactions, e.g burning coal, burning hydrocarbon in an internal combustion engine, lighting a barbeque, are exothermic. The way the problem was set out, with energy listed as a $\text{PRODUCT}$ also suggests that energy was a product, a result of reaction.

Usually, when energy output is reported, the energy associated with an exothermic reaction would be quoted as negative, i.e.

$C {H}_{4} \left(g\right) + 2 {O}_{2} \left(g\right) \rightarrow C {O}_{2} \left(g\right) + 2 {H}_{2} O \left(g\right)$ ;DeltaH^@ =-2855*kJ*mol^-1