Question

Chlorofluorocarbons such as CF2CI2 have been used as refrigerants.. The standard enthalpy of vaporization of CF2Cl2 is 15.4 kJ/mol. Calculate the mass (kg) of liquid CF2CI2 needed to cool 500.0 g of water from 60.0 "C to 40.0 °C. You may need to obtain some data from your textbook when answering this question. Mass of CF2CI2 required:

Answer 1

Given:

m = 500 g

C = 4.184 J/g.oC

Ti = 60 oC

Tf = 40 oC

use:

Q = m*C*(Tf-Ti)

Q = 500.0*4.184*(40.0-60.0)

Q = -41840 J

Q = -41.84 KJ

This heat must be supplied by CF2Cl2

So,

Q for CF2Cl2 = 41.84 KJ

Mol of CF2Cl2 = Q / Hvap

= 41.84 KJ / (15.4 KJ/mol)

= 2.717 mol

Molar mass of CF2Cl2,

MM = 1*MM(C) + 2*MM(F) + 2*MM(Cl)

= 1*12.01 + 2*19.0 + 2*35.45

= 120.91 g/mol

use:

mass of CF2Cl2,

m = number of mol * molar mass

= 2.717 mol * 1.209*10^2 g/mol

= 3.285*10^2 g

Answer: 328 g