# ESPECIAL CASES

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ESPECIAL CASES

PROCESS AT CONSTANT VOLUME

INTRODUCTION:

In this process the volume of thermodynamic system is kept constant by using a container with fixed piston.

MATHEMATICAL FORM:

Since volume does not change

∆V = 0

Therefore

q = ∆E + P∆v

q = ∆E + P(0)

qv = ∆E

CONCLUSION:

According to eq (*) we can say that at constant volume the heat energy absorbed or released by system is utilized to change the internal energy of system.

PROCESS AT CONSTANT PRESSURE

INTRODUCTION:

In the process at constant pressure either a normal atmospheric pressure or a uniform pressure on the piston is maintained throughout.

MATHEMATICAL FORM:

As we know

q = ∆E + P∆y

q = E2- E1+ P(V2- \/1)

q = E2- E1+ PV2- PV1

q = (E2+PV2) – (E1 + PV1)

Let

H = E + PV

H1= E1+ PV1

H2 : E2 + PV2

So that,

q =  H2 – H1

qp = ∆H ——– (*)

CONCLUSION:

According to eq. (*) we can conclude that at constant pressure the total heat energy absorbed or released by system is utilized to change the enthalpy of the system.

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