Single Sex School

TABLE OF CONTENTS

6.1 The Nature of Energy 6.2 Enthalpy and Calorimetry 6.3 Hess’s Law 6.4 Standard Enthalpies of FormaCon 6.5 Present Sources of Energy 6.6

New Energy Sources

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STANDARD ENTHALPIES OF FORMATION

Cgraphite(s)  Cdiamond(s)

ΔH for this process cannot be obtained

by direct measurement in a calorimeter but can be calculated from heats of combusCon.

CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) ΔH° for this process can be calculated from the standard enthalpy of formaCon (ΔHf°).

In Appendix 4

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STANDARD ENTHALPIES OF FORMATION

The standard enthalpy of forma1on of a compound is

the change in enthalpy that accompanies the formaCon of

one mole of a compound from its elements

with all substances in their standard states. 1/2N2(g) + O2(g)  NO2(g)

ΔHf° = 34 kJ/mol ΔHf° = -­‐239 kJ/mol

C(s) + 2H2(g) + 1/2O2(g)  CH3OH(l)

In Appendix 4

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STANDARD ENTHALPIES OF FORMATION
Conven1onal
Defini1ons of Standard States For a Compound,  The standard state of a gaseous substance is a pressure of exactly 1 atm.  For a pure substance in a condensed state (liquid or solid), the standard state is the pure liquid or