Molar Specific Heats

Monday, 7 May 2018

1:29 PM

Gasses also have specific heat properties - and are defined as the amount of heat needed to raise one mole of a gas by 1K

 

 

Where

 - heat required

 - number of moles of gas

 - specific heat of the gas

 - change in temperature (final - initial)

 

But wait, the molar gas constant isn't constant!!!?!?!?

 

At constant volume  -

At constant pressure  -

 

Calculating the Specific Heat under Constant Volume

  • Constant volume means that no work is done on or by the gas.

Recall the first law of thermodynamics -

 

 

 

Calculating the Specific Heat under Constant Pressure

Recall the first law of thermal dynamics -

 

 

Specific Heat Relation

Machine generated alternative text: Table 21.1 Molar specific heats of various gases Molar specific heat (J/mol.K)a Gas Monatomic gases He Ar Diatomic gases C12 Polyatomic gases C02 H 20 CH4 20.8 20.8 20.8 28.8 29.4 34.7 37.0 35.4 35.5 12.5 12.5 12.7 20.4 21.1 25.7 28.5 27.0 27.1 8.33 8.33 8.12 8.33 8.33 8.96 8.50 8.37 8.41 a All values except that for water were obtained at 300 K. = cp/C 1.67 1.67 1.64 1.41 1.40 1.35 1.30 1.30 1.31 Table 21.1, p. 598

 

General Specific Heat Ratio

Ie for monatomic gases (three degrees of freedom)

 

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