# How do you find delta h in a thermochemical equation?

May 26, 2018

How else but by measurement...?

#### Explanation:

And so for a combustion reaction....say the following...

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

...a given mass of methane gas would be combusted, and the heat output used to warm a calorimeter, which may be as simple as a beaker filled with a known mass of water. You will certainly perform this sort of reaction as an undergrad. The point is that this is an experimental phenomenon....and using the heat capacity of water we could access $\Delta {H}_{\text{rxn}}^{\circ}$ as a measurable quantity.

We could approach the $\Delta {H}_{\text{rxn}}^{\circ}$ on the basis of....

DeltaH_"rxn"^@-=DeltaH_f("products")^@-DeltaH_f("reactants")^@

...but we would need more data...