   Chapter 11, Problem 11PS

Chapter
Section
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,

Density=0.7849g/mLVolume=125mLMolarmass=46.07g/molEnthaplyofvaporization,ΔvapH0=42.32kJ/mol

Equation for density is,

Density=MassVolume

Hence,

The mass of ethanol is,

Mass=Density×Volume=(0.7849g1mL)×125mL=98.11g =2

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