PHYSICAL CHEMISTRY IN BRIEF

CHAP. 3: FUNDAMENTALS OF THERMODYNAMICS [CONTENTS] 72

3.2.4 Heat capacities

The heat capacityCfor a given process is defined by the following relation

C=

(

̄dQ

dT

)

process

. (3.16)

U Main unit:JK−^1.
The isochoric heat capacity, CV, and the isobaric heat capacity, Cp, are defined by the
relations

CV =

(

̄dQ

dT

)

izochoric

=

(

∂U

∂T

)

V

, (3.17)

Cp =

(

̄dQ

dT

)

izobaric

=

(

∂H

∂T

)

p

. (3.18)

ForCV andCpwe have

CV > 0 , lim

T→ 0

CV = 0, (3.19)

Cp > 0 , lim

T→ 0

Cp = 0. (3.20)

The relations betweenCV andCpare given in section3.5.1.

Example

The enthalpy of argon at room temperature and pressure obeys the relation

H=

5

2

nRT+ const,

wherenis the amount of substance. What is the heat capacity of argon at constant pressure?

Solution

From the definition (3.18) we obtain

Cp=

5

2

nR.