Class 11th

38. Since, there is an increase in the number of moles on the product side so, entropy increases and ?S is positive.

This is a Short Answer Type Questions as classified in NCERT Exemplar

Molar enthalpy change for graphite (ΔH)

= enthalpy change for 1 g x molar mass of C = -20.7*12 = -2.48 x 102 kJ mol-1

Since the sign of ΔH = -ve, it is an exothermic reaction.

This is a Short Answer Type Questions as classified in NCERT Exemplar

Given that, Cv = heat capacity at constant volume,

Cp = heat capacity at constant pressure

 Difference between Cp and Cv is equal to gas constant (R).

.'. Cp – Cv = nR                                (where, n = no. of moles)

= 10 x 8.314 = 83.14J

This is a Short Answer Type Questions as classified in NCERT Exemplar

For water, molar heat capacity = 18 x Specific heat or Cp = 18 x c

But, specific heat,

C = 4.18 J g^-1 K^-1 Heat capacity,

Cp = 18 x 4.18 JK^-1  = 75.24 JK^-1

36. Graphite has greater entropy since it is loosely packed. At absolute zero the entropy of a substance is zero.

This is a Short Answer Type Questions as classified in NCERT Exemplar

During free expansion, external pressure is zero, so Work done, w = -pextΔV

= -0(5 – 1) = 0

Since the gas is expanding isothermally, therefore, q = 0

ΔU = q + w =0+0=0

35. It is zero.