Chemistry Class 11 NCERT Solutions: Chapter 6 Thermodynamics Part 4

Q: 15 Calculate the enthalpy change for the process

Equation

and calculate bond enthalpy of Equation

Equation

Equation

Equation is enthalpy of atomization

Equation

Answer:

The chemical equations implying to the given values of enthalpies are:

(i) Equation

Equation Equation

(iii) Equation

(iv) Equation

Enthalpy change for the given process Equation can be calculated using the following calculations as:

Equation (ii) +2× Equation (iii) – Equation (i) – Equation (iv)

Equation

Equation

Equation

Bond enthalpy of C-Cl bond in Equation

Equation

Equation

Q: 16. For an isolated system, Equation , what will be Equation ?

Answer:

Equation will be positive i.e., greater than zero

Since Equation will be positive and the reaction will be spontaneous.

Q: 17. For the reaction at Equation ,

Equation

Equation

At what temperature will the reaction become spontaneous considering ∆H and ∆S to be constant over the temperature range?

Answer:

From the expression,

Equation

Assuming the reaction at equilibrium, ∆T for the reaction would be:

Equation

Equation

Equation

Equation

For the reaction to be spontaneous, ∆G must be negative. Hence, for the given reaction to be spontaneous, T should be greater than 2000 K.

Q: 18. For the reaction,

Equation

Answer:

Equation

The given reaction represents the formation of chlorine molecule from chlorine atoms. Here, bond formation is taking place. Therefore energy is being released. Hence, ∆H is negative.

Also, two moles of atoms have more randomness than one mole of a molecule. Since spontaneity is decreased, ∆S is negative for the given reaction.

Q: 19. For the reaction

Equation

Equation

Calculate Equation for the reaction, and predict whether the reaction spontaneously.

Answer: For the given reaction,

Equation

Equation

Equation

Substituting the value of Equation in the expression of Equation

Equation

Equation

Equation

Equation

Substituting the value of Equation in the expression of Equation

Equation

Equation

Equation

Equation

Since Equation for the reaction is positive, the reaction will not occur spontaneously.

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