A sample of 58.90 g solid benzene at 2.4°C was heated until it absorbed 13.5 kJ
ID: 939391 • Letter: A
Question
A sample of 58.90 g solid benzene at 2.4°C was heated until it absorbed 13.5 kJ of heat, at a constant pressure of 1 atmosphere. Using the data given in the table below, determine the final phase and final temperature of the benzene sample.
melting point 5.49°C
boiling point 80.09°C
heat of fusion at 5.49°C: 9.87 kJ/mol
heat of vaporization at 80.09°C: 30.72 kJ/mol
molar heat capacity of solid at 0°C: 118.4 J/mol·K
molar heat capacity of liquid at 25°C: 136.0 J/mol·K
molar heat capacity of gas at 95°C: 103.98 J/mol·K
In its final phase, what will the benzene sample final temperature be?
Explanation / Answer
q = m*s*DT
heating benzene solid to 5.49 c
= (58.9/78)*118.4*(5.49+2.4)
= 705.422 joule. = 0.7 kj
conversion of solid to liquid
= n*DHfus
= (58.9/78)*9.87 = 7.45 kj
energy consumed = 7.45+0.7 = 8.15 kj
heating liquid benzene to 80.09 C
5.35*10^3 = (58.9/78)*136*(x-5.49)
final temperature = x = 57.58 C
so that it is in liquid state.