The internal energy function for a van der Waals gas with constant cV is U(T, v) = n (cV T - a/v), where v is the specific volume. Find the change in temperature Tf - T0 that occurs in a free expansion when the volume changes from V0 to 2V0. Assume that the initial specific volume is 20 L mol-1. Use cV = 2.5 R and the data in Table 5.2 to find the temperature change for nitrogen gas (N2).