ERT 108/3 PHYSICAL CHEMISTRY EXERCISES FIRST LAW OF THERMODYNAMICS Prepared by: Pn. Hairul Nazirah Abdul Halim

Question 1 Calculate the work involved in expanding 20.0 L of an ideal gas to a final volume of 85.0 L against a constant external pressure of 2.50 bar. Ans: -16.25 kJ

Solution To obtain the total work done at constant pressure when the volume change from Vi to Vf;

Question 2 2.00 mol of an ideal gas undergoes isothermal reversible expansion from Pi = 25.0 bar and Vi = 4.50 L to Pf = 4.50 bar. Calculate the work of this process. Ans: -19.3 x 103 J

Solution Calculate the constant temperature at which the process is carried out and the final volume.

2. The work of the isothermal reversible expansion;

Question 3 Relating ΔH and ΔU The internal energy change when 1.0 mol CaCO3 in the form of calcite converts to aragonite is +0.21 kJ. Calculate the difference between the enthalpy change and the change in internal energy when the pressure is 1.0 bar given that the densities of the solids are 2.71 g cm-3 and 2.93 g cm-3 , respectively. Ans: ΔH – ΔU = -0.3 J

Solution

Calculate the volume of aragonite and calcite. Therefore, 1.0 mol CaCO3 (100 g) as aragonite is 34 cm3, and that of 1.0 mol CaCO3 as calcite is 37 cm3.

Question 4 When 2.0 mol CO2 is heated at a constant pressure of 1.25 atm, its temperature increases from 250 K to 277 K. Given that the molar heat capacity of CO2(g) at constant pressure is 37.11 J K-1 mol-1. Calculate q, ΔH and ΔU. Ans: qp= ΔH = 2.0 x 103 J ΔU = 1.6 x 103 J

Solution

Question 5 Consider the adiabatic, reversible expansion of 0.20 mol Ar, initially at 250C, from 0.50 L to 1.00 L. The molar heat capacity of argon at constant volume is 12.48 J K-1 mol-1. Calculate the work of adiabatic, wad. Ans: wad = - 27J

Solution