Q.

One mole of an ideal gas expands isothermally and reversibly from 10 dm3 to 20 dm3 at 300 K. ΔU, q and work done in the process respectively are:

Given: R = 8.3 J K-1 mol-1

ln 10 = 2.3
log 2 = 0.30
log 3 = 0.48                                                            [2025]

1 0, 21.84 kJ, –1.26 kJ  
2 0, –17.18 kJ, 1.718 J  
3 0, 21.84 kJ, 21.84 kJ  
4 0, 1.78 kJ, –1.78 kJ  

Ans.

(4)

w=-2.303 nRTlog10V2V1

w=-2.303×1×8.3×300log102010 J

w=-2.303×1×8.3×300log102 J

w=-2.303×1×8.3×300×0.3 J

w=-1720.341=-1.72 kJ

For an ideal gas undergoing any process: ΔU=nCvΔT

For isothermal process ΔT=0. So ΔU=0.  

By first law of thermodynamics: ΔU=q+w

0=q+w

q=-w=-(-1.72 kJ)=1.72 kJ