Consider one mole of an ideal gas. Which statements are correct?

AIn a reversible isothermal expansion the gas absorbs heat equal in magnitude to the work it does.
BIn an adiabatic free expansion into vacuum, $Δ U = 0$ .
CIn a reversible adiabatic expansion the temperature of the gas remains constant.
DIn an isochoric heating, $Δ H = Δ U$ .

Answer: A, B

(A)

Δ U = 0

q = - w

: true. (B)

q = 0

and

w = 0

(no external pressure), so

Δ U = 0

: true. (C) In a reversible adiabatic expansion

q = 0

and the gas does work at the expense of

U

, so it cools: false. (D)

Δ H = Δ U + n R Δ T

and

Δ T \neq = 0

on heating: false.