   Chapter 18, Problem 10PS

Chapter
Section
Textbook Problem

What information is needed to calculate the entropy change when a 2.25 g sample of liquid water is warmed from 20 °C to 25 °C?

Interpretation Introduction

Interpretation: The information needed for calculating the entropy change for the given reaction which occurs when 2.25g of liquid water warmed from 20oC-25oC should be identified.

Concept introduction: The universe consists of two parts, systems and surroundings. The entropy change for the universe is the sum of entropy change for the system and for surroundings.

ΔS(universe)= ΔS(system)+ΔS(surroundings)whereΔS= Entropy change

The ΔS(universe) should be greater than zero for a spontaneous process.

ΔS(system)=ΔrS°=nS°(products)nS°(reactants)whereΔS= Entropy change

ΔS(surroundings)=ΔrHoTwhereΔS= Entropy changeT=TemperatureΔrHo=Enthalpychange

Explanation

The chemical reaction is liquid water is warmed from 20 °C to 25 °C is indicated as follows,

H2O(l)H2O(g)

The entropy change of universe for any reaction is calculated by the following formula

ΔS(universe)= ΔS(system)+ΔS(surroundings)

Thus, ΔS(system) and ΔS(surroundings) both have to be calculated.

The  ΔS(system) can be calculated by the following expression,

ΔS(system)=ΔrS°=nS°(products)nS°(reactants)

The ΔS(surroundings<

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