Chemistry Class 11 NCERT Solutions: Chapter 6 Thermodynamics Part 2

Q: 7. In a process, Equation of heat is absorbed by a system and Equation work is done by the System. What is the change in internal energy for the process?

Answer:

According to the first law of thermodynamics,

Equation

Where,

Equation Change in internal energy for a process

Equation

Equation

Given,

Equation (Since heat is absorbed)

Equation (Since work is done by the system)

Substituting the values in expression (i), we get

Equation

Equation

Hence, the change in internal energy for the given process is Equation

Q: 8. The reaction of cyanamide, Equation with dioxygen was carried out a bomb calorimeter, and ∆U was found to be Equation Calculate enthalpy change for the reaction at Equation

Equation

Answer:

Enthalpy change for a reaction (∆H) is given by the expression,

Equation

Where,

Equation

Equation change in number of moles

For the given reaction,

Equation

Equation

Equation

And,

Equation

Equation

Equation

Substituting the values in the expression of ∆H:

Equation

Equation

Equation

Q: 9. Calculate the number of kJ of heat necessary to raise the temperature of Equation of aluminium from Equation Molar heat capacity of Al is Equation

Answer

From the expression of heat (q),

Equation

Where,

Equation

Equation

Equation

Substituting the values in the expression of q:

Equation

Equation

Equation

Q: 10. Calculate the enthalpy change on freezing of Equation of water at Equation to ice at - Equation

Equation

Equation

Answer:

Total enthalpy change involved in the transformation is the sum of the following changes:

(A) Energy change involved in the transformation of mol of water at Equation

(B) Energy change involved in the transformation of Equation

(C) Energy change involved in the transformation of Equation

Equation

Equation

Equation

Equation

Equation

Hence, the enthalpy change involved in the transformation is Equation

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