Question

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`

Answer 1

Clearly, the reaction is `"exothermic"`.

Explanation:

You are burning ethane; normally, the gas supplied to homes and labs is methane, `CH_4`.

`CH_4(g) +2O_2(g) rarr CO_2(g) +2H_2O(g)`

The stability of the `C=O` and `O-H` bonds means that energy is released upon their formation, and the reaction is `"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 `"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.

`CH_4(g) +2O_2(g) rarr CO_2(g) +2H_2O(g)` `;DeltaH^@ =-2855*kJ*mol^-1`