Chapter 12, Problem 40PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
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 Â°C to its boiling point, condense the gas, and cool the liquid to â€“40.0 Â°C.

TheÂ energyÂ canÂ beÂ calculatedÂ byÂ usingÂ followingÂ formula,Â qÂ =â€‰mÂ Ã—Â cÂ Ã—Â Î”TÂ â€‰MassÂ (m)â€‰=â€‰20.0Â gMolarÂ massÂ ofÂ CCl2F2=â€‰120.91molarÂ heatÂ capacityÂ (c)Â =â€‰117.2â€‰J/mol.KÎ”TÂ â€‰=â€‰243.4K-Â 313.2Kâ€‰=â€‰-69.8â€‰KqÂ =â€‰mÂ Ã—Â cÂ Ã—Â Î”TÂ qÂ =â€‰20gÂ Ã—Â 117.2â€‰J/mol.K120.91Â Ã—Â (-Â 69.8â€‰K)â€‰=â€‰-Â 1353JÂ qÂ =â€‰â€‰-Â 1353JÂ

Condense the gas:

Â TheÂ energyÂ canÂ beÂ calculatedÂ byÂ usingÂ followingÂ formula,Â qÂ =â€‰mÂ Ã—Â cÂ Ã—Â DTÂ â€‰MassÂ (m)â€‰=â€‰20.0Â gMolarÂ massÂ ofÂ CCl2F2=â€‰120.91molarÂ heatÂ capacityÂ (c)Â =â€‰117.2â€‰J/mol.KDTÂ â€‰=â€‰243.4K-Â 313.2Kâ€‰=â€‰-69.8â€‰KqÂ =â€‰mÂ Ã—Â cÂ Ã—Â DTÂ qÂ =â€‰20

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