Show that the heat absorbed at constant pressure is equal to the chang

1.	Show that the heat absorbed at constant pressure is equal to the change in enthalpy of the system.OR Why is enthalpy called heat content of the system?
Answer» By the first law of thermodynamics, ΔU = Q + W Where ΔU is the change in internal energy Q is heat supplied to the system W is the work obtained. ∴ Q = ΔU – W If Q_P is the heat absorbed at constant pressure by the system, so that the volume changes by ΔV against constant pressure P then, W = -PΔV ∴ Q = ΔU – (-PΔV) ∴ Q = ΔU + PΔV ……… (1) If ΔH is the enthalpy change for the system, then ΔH = ΔU + PΔV ……….. (2) By comparing above equations, (1) and (2), we can write, Q_P = ΔH Hence heat absorbed at constant pressure is equal to the enthalpy change for the system. Since by increase in enthalpy heat content of the system increases, enthalpy is also called as the heat content of the system.

Show that the heat absorbed at constant pressure is equal to the change in enthalpy of the system.OR Why is enthalpy called heat content of the system?

Answer»

By the first law of thermodynamics,

ΔU = Q + W

Where ΔU is the change in internal energy

Q is heat supplied to the system

W is the work obtained.

∴ Q = ΔU – W

If Q_P is the heat absorbed at constant pressure by the system, so that the volume changes by ΔV against constant pressure P then,

W = -PΔV

∴ Q = ΔU – (-PΔV)

∴ Q = ΔU + PΔV ……… (1)

If ΔH is the enthalpy change for the system, then

ΔH = ΔU + PΔV ……….. (2)

By comparing above equations, (1) and (2), we can write,

Q_P = ΔH

Hence heat absorbed at constant pressure is equal to the enthalpy change for the system. Since by increase in enthalpy heat content of the system increases, enthalpy is also called as the heat content of the system.

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