Question

Consider the generic chemical equation below. X + Ymc021-1.jpg W + Z Reactant X contains 199.3 J of chemical energy. Reactant Y contains 272.3 J of chemical energy. Product W contains 41.9 J of chemical energy. If the reaction loses 111.6 J of chemical energy as it proceeds, how much chemical energy must product Z contain?

Answer 1

The reaction is:

X + Y → W + Z

Chemical energy of reactant X = 199.3 J = Ux

Chemical energy of reactant Y = 272.3 J = Uy

Chemical energy of Product W = 41.9 J = Uw

Chemical energy of Product Z = ? = Uz

Where reaction loses energy = 111.6 J = ΔU

By using the equation:

(Ux + Uy) – (Uw + Uz) = ΔU

Ux + Uy – Uw – Uz = ΔU

Uz = Ux + Uy – Uw –ΔU

Uz = 199.3 + 272.3 – 41.9 – 111.6

Uz = 318.1 J

Product Z must contain 318.1 J chemical energy.