Question

A gas absorbs 250 J of heat and expands from 1 dm³ to 10 dm³ at constant temperature against external pressure of 0.5 bar. The values of Q, W and ∆U will be respectively ____________.

Options

• 250 J, 450 J, 710 J

• 250 J, −450 J, 700 J

• 250 J, −450 J, −200 J

• −250 J, 450 J, 200 J

Answer 1

A gas absorbs 250 J of heat and expands from 1 dm³ to 10 dm³ at constant temperature against external pressure of 0.5 bar. The values of Q, W and ∆U will be respectively 250 J, −450 J, −200 J.

Explanation:

P = 0.5 bar, V₂ = 10 dm³, V₁ = 1 dm³, Q = 250 J

W = −P_ext (V₂ − V₁)

= −0.5 bar × (10 − 1) dm³

= −4.5 bar dm³

= `-4.5  "dm"^3  "bar" xx 100 "J"/("dm"^3  "bar")`

= −450 J

∆U = Q + W

= 250 + (−450)

= −200 J