Hess’s Law: One Reaction

Question

The standard enthalpy change for the following reaction is 2.11×10³ kJ at 298 K.

1. UF₆(g)  U(s) + 3 F₂(g)    ΔH° = 2.11×10³ kJ

What is the standard enthalpy change for this reaction at 298 K?

U(s) + 3 F2(g)  UF6(g)

 _____kJ

Answer 1

Note that the second equation is the reverse of the first.

If heat is gained in one direction, then it must be lost in the opposite direction. Thus for the second equation

ΔH° = -2.11×10³kJ