Question

Calculate the energy change for a pure substance over a temperature range. The following information is given for benzene at I am: boiling point = 80.10 °C melting point = 5.500°C specific heat gas = 1.040 J/g °C AHp 80.10 °C) 393.3 Jg AH5.500 °C) - 127.4 g specific heat liquid - 1.740 J/g °C. A 21.10 g sample of liquid benzene is initially at 55.90 °C. If the sample is heated at constant pressure (P= I atm), calculate the amount of energy in I needed to raise the temperature of the sample to 102.00 °C.

Answer 1

the total heat is divided into three separate processes:

1) Liquid benzene at 55.9 0C to benzene at 80.10 0C:

Heat = mass * specific heat * temperature difference = 21.1 * 1.740 * (80.1 - 55.9) = 888.48 J = 0.888 KJ

2) Liquid benzene to gaseous benzene: heat = mass * latent heat of vaporisation = 21.1 * 393.3 = 8.299 KJ

3) benzene vapor at 80.1 to vapor at 102 0C = mas s* specific heat * temp change = 21.1 * 1.04 * (102 - 80.1) = 480.57 J = 0.481 KJ

Total heat = sum of heat in all processes = 0.888 + 8.299 + 0.481 = 9.66 kJ