Class 11th

For an ideal gas, the work of reversible expansion under isothermal condition can be calculated by using the expression w= -nRTln $\frac{V_f}{V_i}$

A sample containing 1.0 mol of an ideal gas is expanded isothermally and reversibly to ten times of its original volume, in two separate experiments. The expansion is carried out at 300 K and at 600 K respectively. Choose the correct option.

(i) Work done at 600 K is 20 times the work done at 300 K.

(ii) Work done at 300 K is twice the work done at 600 K.

(iii) Work done at 600 K is twice the work done at 300 K.

(iv) ∆U = 0 in both cases.

The spontaneity means, having the potential to proceed without the assistance of external agency. The processes which occur spontaneously are (i) flow of heat from colder to warmer body. (ii) Gas in a container contracting into one corner. (iii) Gas expanding to fill the available volume. (iv) Burning carbon in oxygen to give carbon dioxide.

In an exothermic reaction, heat is evolved, and system loses heat to the surroundings. For such system

(i) qp will be negative

(ii) ∆_rH will be negative

(iii) qp will be positive

(iv) ∆_rH will be positive

Thermodynamics mainly deals with

(i) Interrelation of various forms of energy and their transformation from one form to another.

(ii) Energy changes in the processes which depend only on initial and final states of the microscopic systems containing a few molecules.

(iii) How and at what rate these energy transformations are carried out.

(iv) The system in equilibrium state or moving from one equilibrium state to another equilibrium state.

Which of the following is not correct?

(i) ∆G is zero for a reversible reaction

(ii) ∆G is positive for a spontaneous reaction

(iii) ∆G is negative for a spontaneous reaction

(iv) ∆G is positive for a non-spontaneous reaction

Enthalpy of sublimation of a substance is equal to

(i) Enthalpy of fusion + enthalpy of vapourisation

(ii) Enthalpy of fusion

(iii) Enthalpy of vapourisation

(iv) Twice the enthalpy of vapourisation

The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound

(i) Is always negative

(ii) Is always positive

(iii) May be positive or negative

(iv) Is never negative

Consider the reactions given below. On the basis of these reactions find out which of the algebric relations given in options (i) to (iv) is correct?

(a) C (g) + 4H (g) → CH₄ (g); ∆r H = x kJ/ mol

(b) C (graphite,s) + 2H₂ (g) → CH₄ (g); ∆rH = y kJ /mol

(i) x = y

(ii) x = 2y

(iii) x > y

(iv) x < y

On the basis of thermochemical equations (a), (b) and (c), find out which of the algebric relationships given in options (i) to (iv) is correct.

(a) C (graphite) + O₂ (g) → CO₂ (g) ; ∆_rH = x kJ/ mol

(b) C (graphite) + $\frac{1}{2}$ O₂ (g) → CO (g) ; ∆_rH = y kJ/ mol

(c) CO (g) $\frac{1}{2}$ +  O2 (g) → CO₂ (g) ; ∆_rH = z kJ/ mol

(i) z = x + y

(ii) x = y – z

(iii) x = y + z

(iv) y = 2z – x

Assertion (A): Among isomeric pentanes, 2, 2-dimethylpentane has highest boiling point. 

Reason (R): Branching does not affect the boiling point. 

(i) Both A and R are correct and R is the correct explanation of A. 

(ii) Both A and R are correct but R is not the correct explanation of A. 

(iii) Both A and R are not correct. 

(iv) A is not correct but R is correct.