Class 11th

4.The chemical equation for the combustion reaction is:

CH₄  (g) + 2O₂  (g) →CO₂  (g) + 2H₂O (l)

Δ_ng= 1 – 3 = -2

ΔH^? = ΔU^?  + Δ_ngRT = ΔU^? - 2RT

Therefore, ΔH^?  <ΔU^?

i.e. option (iii) is correct.

1. (ii) whose value is independent of path

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

At constant volume

q = ΔU + (-w)

-w = pΔ q = AU + pΔV

ΔV = 0 (at constant volume)

Hence, qv = ΔU + 0 = ΔU= change in internal energy at constant pressure, qp = AU + pΔV

Since ΔU + pΔV=ΔH

=> qp = ΔH change in enthalpy

Hence, at constant volume and at constant pressure, heat change is a state function because it is equal to ΔU and ΔH respectively which are state functions.

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

For an isolated system w = 0, q = 0

Since ΔU= q + w = 0 + 0 = 0, ΔU= 0

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

Gibbs energy for a reaction in which all reactants and products are in standard state. ΔrG° is related to the equilibrium constant of the reaction as follows

ΔrG = ArG° + RT In K

At equilibrium, 0 = ΔrG° + RT InA– ( {ΔrG = 0) or  ΔrG° =-RT lnK

ΔrG° = 0 when K= 1

For all other values of K, ArG° will be non-zero.