ERT 108/3 – PHYSICAL CHEMISTRYTUTORIAL 1

Exercise 1.1(b)

(a) Could 25 g of argon gas in a vessel of volume 1.5 dm3 exert a pressure of 2.0 bar at 30°C if it behaved as a perfect gas? If not, what pressure would it exert?

(b) What pressure would it exert if it behaved as a van der Waals gas?

Ans: a) p = 10.5 bar b) p = 10.4 bar

Problem 1.8

At 273 K measurements on argon gave B = - 21.7 cm3 mol-1 and C = 1200 cm6 mol -2, where B and C are the second and third virial coefficients in the expansion of Z in powers of l/Vm. Assuming that the perfect gas law holds sufficiently well for the estimation of the second and third terms of the expansion, calculate the compression factor of argon at 100 atm and 273 K. From your result, estimate the molar volume of argon under these conditions.

Ans: Vm = 0.208 dm3

Exercise 2.14(b)

A sample of 5.0 mol CO2 (g) is originally confined in 15 dm3 at 280 K and then undergoes adiabatic expansion against a constant pressure of 78.5 kPa until the volume has increased by a factor of 3.0. Calculate q, w, ΔT, ΔH and ΔU. (The final pressure of the gas is not necessarily 78.5 kPa)

Ans: w = ΔU= -3.5 x 103 J, ΔT = -24 K, ΔH = -4.5 x 103 J

Problem 2.4

A sample of 70 mmol Kr(g) expands reversibly and isothermally at 373 K from 5.25 cm3

to 6.29 cm3, and the internal energy of the sample is known to increase by 83.5 J. Use the virial equation of state up to the second coefficient B = - 28.7 cm3 mol-1 to calculate w, q, and ΔH for this change of state.

Ans: w = -25 J, ΔU = +83.5 J, q = 109 J, and ΔH = +97 J

Exercise 2.18(b)

The standard enthalpy of formation of phenol is - 165.0 kJ mol-1. Calculate its standard enthalpy of combustion.

Ans: -3053.6 kJ/mol

Exercise 2.19(b)

From the following data, determine for diborane, B2H6 (g), at 298 K:

Ans: = +36.6 kJ/mol