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

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Question: 58

Derive the relationship between ΔH and ΔU for an ideal gas. Explain each term involved in the equation.

Answer:

Question: 59

Extensive properties depend on the quantity of matter but intensive properties do not. Explain whether the following properties are extensive or intensive.

Mass, internal energy, pressure, heat capacity, molar heat capacity, density, mole fraction, specific heat, temperature and molarity

Answer:

Hint: Ratio of two extensive properties is always intensive

Question: 60

The lattice enthalpy of an ionic compound is the enthalpy when one mole of an ionic compound present in its gaseous state, dissociates into its ions. It is impossible to determine it directly by experiment. Suggest and explain an indirect method to measure lattice enthalpy of .

Answer:

Bonn - Haber Cycle

Steps to measure lattice enthalpy from Bonn - Haber cycle

Sublimation of sodium metal

(1)

(2) Ionisation of sodium atoms

, ionisation enthalpy

(3) Dissociation of chlorine molecule

i.e., One-half of bond dissociation enthalpy.

(4)

NaCl dissolution

NaCl Dissolution

Question: 61

is net energy available to do useful work and is thus a measure of “free energy”. Show mathematically that is a measure of free energy. Find the unit of . If a reaction has positive enthalpy change and positive entropy change, under what condition will the reaction be spontaneous?

Answer:

For spontaneous change,

But,

Unit of is Joule

• The reaction will be spontaneous at high temperature.

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