One mole of a gas is placed in a closed system with a 20 l vessel initially at t = 300 k. the vessel is then isothermally expanded to 40 l. the gas follows the equation of state: p = rt/v + a/v2 where a = 240 l2 · atm/mol2 and r = 0.08206 l · atm/ mol · k. a. derive an expression relating (dh/dv)t to measurable properties. b. find dh for the gas in this process.