n(Ar) = 4.000 / 39.95 = 0.1001mol
由于理想气体等温膨胀,所以:ΔU = ΔH = 0
由 ΔU = Q + W 得:Q = W
Q、W 为过程量,其值与过程方式有关,
(1)若发生可逆过程:
Q(R) = W(R) = nRTln(p1/p2) = 0.1001×8.314×300×ln(506.6/202.6) = 228.9 J
ΔS = Q(R) / T = 0.763 J·K-1
(2)若发生不可逆过程:
ΔU、ΔH、ΔS为状态函数,则:
ΔU = ΔH = 0,
ΔS = 0.763 J·K-1
Q(IR) = W(IR) = p外(V2 - V1)
= p2(V2 - V1) = nRT( 1- p2/p1) = 149.9 J