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Thermodynamics

Short Answer Type

141.

How will you distinguish between intensive and extensive properties?

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Long Answer Type

142.

What do you mean by internal energy and internal energy change?

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143. Derive an expression for pressure-volume work (PV – work).

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144.
Derive an expression for work done in isothermal reversible expansion of ideal gas.

Let us consider n moles of ideal gas enclosed in a cylinder fitted with a weightless and frictionless piston. The work of expansion for a small change of volume dV against the external pressure P is given by

Total work done when the gas expands from initial volume V₁ to final volume V₂, will be

For an ideal gas, PV = nRT i.e.

Hence,

For isothermal expansion, T = constant so that

But at constant temperature,

P₁V₁ = P₂V₂

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Short Answer Type

145.

Calculate the maximum work obtained when 0.75 mol of an ideal gas expands isothermally and reversibly at 27°C from a volume of 15L to 25L.

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146.

State first law of thermodynamics in different ways.

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147.

If water vapour is assumed to be a perfect gas,
molar enthalpy change for vapourisation of 1 mol of water at 1bar and 100°C is 41kJ mol^–1. Calculate the internal energy change, when

(i) 1 mol of water is vaporised at 1 bar pressure and 100°C.

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