Question

In an adiabatic expansion, a gas does 25 J of work, while in an adiabatic compression 100 J of work is done on a gas. The change of internal energy in the two processes respectively, are ______.

विकल्प

• 25 J and -100 J

• -25 J and 100 J

• -25 J and -100 J

• 25 J and 100 J

Answer 1

In an adiabatic expansion, a gas does 25 J of work, while in an adiabatic compression 100 J of work is done on a gas. The change of internal energy in the two processes respectively, are -25 J and 100 J.

Given data:

work done in adiabatic expansion = 25 J

work done in adiabatic compression = 100 J

In adiabatic process, no exchange of heat takes place, i.e., ΔQ = O

From first law of thermodynamics 

Q = u + w

O = u + w

u = -w                      ...(i)

for adiabatic expansion, change in internal energy is 

w = 25 J

∴ from (i) Δu = -w = -25 J

for adiabatic compression

w = -100 J

∴ Δu = -(w) = -(-100)        ...(from i)

Δu = 100 J