Chemistry Class-11: Chapter –6. Thermodynamics Part – 5

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Question: 31

A sample of of a monatomic ideal gas is taken through a cyclic process of expansion and compression as shown in Fig. 6.1. What will be the value of for the cycle as a whole?

A sample of 1.0 mol of a monatomic ideal gas

PV Curve

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Answer:

Question: 32

The standard molar entropy of . Will the standard molar entropy of be more, or less than ?

Answer:

Less, because ice is more ordered than

Question: 33

Identify the state functions and path functions out of the following: enthalpy, entropy, heat, temperature, work, free energy.

Answer:

State Functions: Enthalpy, Entropy, Temperature, Free energy Path Functions: Heat, Work

Question: 34

The molar enthalpy of vapourisation of acetone is less than that of water. Why?

Answer:

Because of strong hydrogen bonding in water, its enthalpy of vapourisation is more.

Question: 35

Which quantity out of and will be zero at equilibrium?

Answer:

will always be zero

is zero for because , will be non zero for other values of .

Question: 36

Predict the change in internal energy for an isolated system at constant volume.

Answer:

For isolated system, there is no transfer of energy as heat or as work i.e., . According to the first law of thermodynamics

Question: 37

Although heat is a path function but heat absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.

Answer:

At constant volume

By first law of thermodynamics:

, since volume is constant.

change in internal energy

At constant pressure

But,

Change in enthalpy.

So, at a constant volume and at constant pressure heat change is a state function because it is equal to change in internal energy and change in enthalpy respectively which are state functions.

Question: 38

Expansion of a gas in vacuum is called free expansion. Calculate the work done and the change in internal energy when litre of ideal gas expands isothermally into vacuum until its total volume is litre?

Answer:

For isothermal expansion

By first law of thermodynamics