Reactant A contains 85.1 J of chemical energy. Reactant B contains 87.9 J of chemical energy. Product C contains 38.7 J of chemical energy. If the reaction absorbs 104.3 J of chemical energy as it proceeds, how much chemical energy must product D contain?

The reaction would proceed like: A + B - - > C + D. We then consider that each has a stoichiometric coefficient of 1 for each of the reactant and product. Hence, algebraically, this problem can be presented as follows:

(38.7+X) - (85.1+87.9) = - 104.3

Then x = 31 J

This is the amount of energy D must contain.

Answer: 238.6 J

Explanation:

1) Chemical energy is indicated as enthalpy

2) Energy balance:

∑ enthalpy of the reactants + energy added = ∑ enthalpy of the products + energy released.

3) ∑ enthalpy of the reactants = 85.1 J + 87.9 J = 173 J

4) energy added = 104.3 J

5) ∑ enthalpy of the products = 38.7 J + D

6) energy released = 0

7) Equation:

173J + 104.3J = 38.7 + D + 0

⇒ D = 173J + 104.3J - 38.7J = 238.6J, which is the chemical energy of the product D.