Question

Physical Chemistry:

Calculate ΔG for the isothermal compression of 10.0 g of water from 1.0 atm to 100.0 atm at 25°C

Answer 1

For an isothermal process U = 0   & H = 0

So from first law of thermodynamics w = G = -nRT ln (P/P')

Where

n = number of moles of water = mass / molar mass

   = 10.0 g / 18(g/mol)

   = 0.55 mol

R = gas constant = 8.314 J-mol /K

P = initial pressure = 1.0 atm

P' = final pressure = 100.0 atm

T = temperature = 25 ^oC = 25+273 = 298 K

Plug the values we get w = G = -nRT ln (P/P')

                                                   = -(0.55 x8.314 x298 ) x ln ( 1.0 / 100.0 )

                                                  = +6275.3 J

                                                  = +6.27 kJ

Therefore G = +6.27 kJ