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AT
CONSTANT PREESURE
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| Heat
supplied at constant pressure is also known as "ISOBARIC PROCESS".
An isobaric process is one in which no pressure change
takes place during the supply of heat to system. |
| In
order to understand an isobaric process consider a cylinder fitted with
a frictionless piston, the piston is free to move. An
ideal gas is enclosed in the cylinder. |
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| Let
the internal energy of the system at initial state is E1, the
temperature of system is T1, volume of gas
is V1 and pressure is P. |
| If
qp amount of heat is supplied to the system, its internal energy
will increase from E1 to E2 and the temperature
of system also rises from T1 to T2, |
| At
the same time gas exerts some pressure on the piston, since the piston is
free to move, it displaces by
"h" the volume of gas increases from V1 to V2
. Due to increase in volume, pressure again decreases to
its original value i.e. P1. |
| ACCORDING
TO THE FIRST LAWOFTHERMODYNAMICS |
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Qp
= DE + work
Qp = DE
+ P DV
Qp
= DE + P DV but
(DE = E2- E1)
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Qp
= E2-E1 + P (V2 – V1)
Qp
= E2-E1 + PV2- PV1
Qp
= E2+ PV2 – E1 – PV1
Qp = (E2+ PV2) – (E1+ PV1)
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but
(E + PV =H)
(H= enthalpy)
therefore,
qP = D
H
OR
q p = DE
+ P DV =D
H
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CONCLUSION
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| This
expression indicates that heat supplied at constant pressure is equal to
increase in enthalpy of system. |
| For
latest information , free computer courses and high impact notes visit :
www.citycollegiate.com |
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