Previous Year Papers

Download Solved Question Papers Free for Offline Practice and view Solutions Online.

Test Series

Take Zigya Full and Sectional Test Series. Time it out for real assessment and get your results instantly.

Test Yourself

Practice and master your preparation for a specific topic or chapter. Check you scores at the end of the test.

Thermodynamics

Short Answer Type

141.

How will you distinguish between intensive and extensive properties?

440 Views

Long Answer Type

142.
What do you mean by internal energy and internal energy change?

The total energy stored by a fixed amount of the substance is called its internal energy or intrinsic energy and is denoted by U. It is the sum of various forms of energies such as kinetic energy of translation, rotation and vibration, potential energy due to intermolecular forces, the chemical bond energy and electronic and nuclear energies of the constituent atoms.

Internal energy is a function of state only. It is not possible to determine the absolute value of internal energy as most of the constituent energies cannot be precisely determined. However, we are more interested in knowing the change in internal energy (∆U).

Change in internal energy (∆U): It may be defined as The difference in internal energies of the product and reactant species taking part in a chemical reaction at constant volume. For example, if U_R represents the internal energy of the reactants and Up represents the internal energy of the products, then

where ∆U gives the change in internal energy.

In a chemical reaction, ∆U has always noticed in the form of heat evolved or absorbed during the reaction in case the reaction is carried out at constant volume. Hence internal energy change (∆U) is equal to the heat evolved or absorbed in a chemical reaction at constant volume and constant temperature.

Clearly, if

the extra energy possessed by the system in the initial state (or the reactants) would be given out and

will be negative.

Similarly, if

energy will be absorbed in the process and

will be positive.
Units of U: The units of energy are ergs (in CGS units) or joules (in S.I. units)
1 Joule = 10⁷ ergs.

166 Views

143. Derive an expression for pressure-volume work (PV – work).

874 Views

144.

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

1559 Views

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.

111 Views

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.

319 Views