# How is an endothermic reaction identified in an equation?

Jul 20, 2018

Well, how is an exothermic reaction represented?

#### Explanation:

We use the symbol $\Delta$ to represent heat...i.e. for a combustion reaction....

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

And certainly $\Delta {H}_{\text{rxn"=DeltaH_"combustion of methane}}$...and this could be very accurately measured. And we represent an endothermic reaction equivalently but energy appears on the left hand side as we face the equation. That is energy, $\Delta H$, is A REACTANT.

And an example of spontaneous endothermic change...the which will probably be demonstrated in your lab..

$B a {\left(O H\right)}_{2} \cdot 8 {H}_{2} O \left(s\right) + 2 N {H}_{4} C l \left(s\right) + \Delta \rightarrow B a C {l}_{2} \cdot 2 {H}_{2} O \left(s\right) + 2 N {H}_{3} \left(a q\right) + 8 {H}_{2} O \left(l\right)$

The two solids are mixed, and we get a slurry of barium salt, a whiff of ammonia gas, and the sides of the flask ice up as the entropy-driven reaction extracts heat from the surroundings...