   Chapter 12, Problem 40PS

Chapter
Section
Textbook Problem

If your air conditioner is more than several years old, it may use the chlorofluorocarbon CCl2F2 as the heat transfer fluid. The normal boiling point of CCl2F2 is −29.8 °C, and the enthalpy of vaporization is 20.11 kJ/mol. The gas and the liquid have molar heat capacities of 117.2 J/mol · K and 72.3 J/mol · K, respectively. How much energy is evolved as heat when 20.0 g of CCl2F2 is cooled from +40 °C to −40 °C?

Interpretation Introduction

Interpretation:

The total energy evolved as heat energy has to be calculated.

Concept introduction:

The energy can be calculated by using following formula,

q =m × c × ΔT

Explanation

The total heat can be calculated the required is the sum of the heat required to cool the gas from 40.0 °C to its boiling point, condense the gas, and cool the liquid to –40.0 °C.

The energy can be calculated by using following formula, q =m × c × ΔT Mass (m)=20.0 gMolar mass of CCl2F2=120.91molar heat capacity (c) =117.2J/mol.KΔT =243.4K- 313.2K=-69.8Kq =m × c × ΔT q =20g × 117.2J/mol.K120.91 × (- 69.8K)=- 1353J q =- 1353J

Condense the gas:

The energy can be calculated by using following formula, q =m × c × DT Mass (m)=20.0 gMolar mass of CCl2F2=120.91molar heat capacity (c) =117.2J/mol.KDT =243.4K- 313.2K=-69.8Kq =m × c × DT q =20

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