   Chapter 5, Problem 103SCQ

Chapter
Section
Textbook Problem

You want to determine the value for the enthalpy of formation of CaSO4(s), but the reaction cannot be done directly.Ca(s) + S(s) + 2 O2(g) → CaSO4(s)You know, however, that (a) both calcium and sulfur react with oxygen to produce oxides in reactions that can be studied calorimetrically, and (b) the basic oxide CaO reacts with the acidic oxide SO3(g) to produce CaSO4(s) with △rH° = −402.7 kJ. Outline a method for determining △fH° for CaSO4(s), and identify the information that must be collected by experiment. Using information in Appendix L, confirm that △fH° for CaSO4(s) = −1433.5 kJ/mol.

Interpretation Introduction

Interpretation:

The standard enthalpy of formation of CaSO4 has to be determined.

Concept Introduction:

The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one gram of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.

ΔrH0=ΣnΔfH0(products)-ΣnΔfH0(reactants)

Explanation

Given reaction is:

CaO+SO3CaSO4                ΔrH0=-402.7kJ

From appendix,

ΔfH0(CaO) = -635.05kJ/mol

ΔfH0(SO3) = -395.77kJ/mol

Substitute the values ΔrH0

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