Chapter 11, Problem 11PS

### 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

# Ethanol, CH3CH2OH, has a vapor pressure of 59 mm Hg at 25 °C. What quantity of energy as heat is required to evaporate 125 mL of the alcohol at 25 °C? The enthalpy of vaporization of the alcohol at 25 °C is 42.32 kJ/mol. The density of the liquid is 0.7849 g/mL.

Interpretation Introduction

Interpretation: The energy required to evaporate the given volume of alcohol has to be determined.

Concept Introduction:

The energy required to overcome the intermolecular forces of attraction for 1mol of a substance is called standard enthalpy of vaporization,ΔvapH0

Equation for density is,

Density=MassVolume

From its given mass is,

Number of moles=GivenmassMolecularmass

Explanation

Given,

Densityâ€‰=â€‰0.7849g/mLVolumeâ€‰=â€‰125mLMolarâ€‰massâ€‰=â€‰46.07â€‰g/molEnthaplyâ€‰ofâ€‰vaporization,Î”vapH0â€‰=â€‰42.32kJ/mol

Equation for density is,

â€‚Â Densityâ€‰â€‰=â€‰â€‰â€‰MassVolumeâ€‰

Hence,

The mass of ethanol is,

â€‚Â Massâ€‰=â€‰DensityÃ—â€‰Volume=â€‰(0.7849g1mL)â€‰Ã—â€‰125mL=â€‰98.11â€‰g =2

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