Consider the following changes at constant temperature and pressure:
H₂O(s) → H₂O(l) ; ΔH₁
H₂O(l) → H₂O(g) ; ΔH₂
H₂O(g) → H₂O(s) ; ΔH₃
Using Hess's law,the sum ΔH₁ + ΔH₂ + ΔH₃ is

Question

Quizplus · Accepted Answer

Hess's law states that the overall enthalpy change of a reaction can be calculated by adding the enthalpy changes of the individual steps in the reaction. In this case, the three steps form a closed loop. Therefore, ΔH for the overall reaction is equal to zero as the energy required to go from solid to liquid to gas and then back to solid state is exactly balanced by the energy released going in the opposite direction.

Consider the Following Changes at Constant Temperature and Pressure