How is an endothermic reaction identified in an equation?

1 Answer
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....

CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(l) + Delta.

And certainly DeltaH_"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, DeltaH, is A REACTANT.

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

Ba(OH)_2*8H_2O(s) + 2NH_4Cl(s) +Deltararr BaCl_2*2H_2O(s) + 2NH_3(aq) + 8H_2O (l)

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...