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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).

Let us consider a gas enclosed in a cylinder fitted with a frictionless piston having an area of cross-section equal to ‘a’. Let the gas expand against the external pressure P facing the piston to move through a small distance d. Then work of expansion is given by,

During expansion, work is done by the system and ∆V(V₂ – V₁) is positive. Therefore, in order to satisfy the sign conventions, a negative sign is put in the expression for work.

During compression, Work is done on the system. ∆V(V₂ – V₁) for compression is negative. Therefore work, as obtained from the above expression, comes out to be positive and satisfies the conventions.
The general expression for all types of PV-work is given by

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144.

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

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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.

1092 Views

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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