PPT Slide

38

• _H varies with conditions, so use _H values representing standardized conditions, to compare thermodynamic data.

The standard states are:

• For a gas, the standard state is 1 atm.

• For a substance in aqueous solution, the standard state is 1 M concentration (1 M = 1 mol/L).

• For an element or compound, the standard state is the most stable  form at 1 atm and the temperature of interest; usually 25ƒC (298 K).

• _H rxn measured with all substances in their standard states, is the  standard heat of reaction, _Hƒ rxn .

Concept 6-13. The meaning of a formation equation and the

standard heat of formation

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