PPT Slide

5

Generalizations (whether exothermic or endothermic):

• Within a state, a change in heat causes a change in temperature and in  average E k as the most probable speed of the molecules changes.

• During a change of state, a change in heat occurs at constant temperature,  but E p changes with the average distance between molecules.

• By Hessís law, the total heat released during the process is the sum of  the heats released during the individual stages:

(Use molar heat capacity.)

Stage 1: H 2O(g) [130ƒC] =H 2O(g) [100ƒC]

• Follow a 2.50 mol sample of H 2O as it changes from gaseous water at 1  atm and 130ƒC to ice at ñ 40ƒC in five stages.

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