• A brief illustration
To calculate the entropy change in the surroundings when 1.00 mol H2O(l) is formed
from its elements under standard conditions at 298 K, we use ΔH 7 = −286 kJ from
Table 2.8. The energy released as heat is supplied to the surroundings, now regarded as
being at constant pressure, so qsur = +286 kJ. Therefore,
ΔSsur = =+960 J K−1
This strongly exothermic reaction results in an increase in the entropy of the surroundings
as energy is released as heat into them. •