PHYSICAL CHEMISTRY IN BRIEF

CHAP. 5: THERMOCHEMISTRY [CONTENTS] 127

Chapter 5

Thermochemistry

Thermochemistry in a strict sense of the word means that part of thermodynamics which deals
with heat released during chemical reactions, or heat that has to be supplied in order for a
reaction to take place. In a broader sense of the word, thermochemistry deals with the changes
in thermodynamic quantities of chemically reacting systems.
We will write the general chemical reaction either in the form

aA +bB +···=rR +sS +···, (5.1)

wherea,b,... ,r,s,... represent the stoichiometric coefficients while the capital letters indicate
the reactants, or in a more compact form

0 =

∑n

i=1

νiRi, (5.2)

whereνi is the stoichiometric coefficient of substance Riandnis the number of substances
participating in the reaction. Note that when we use the form (5.2), theνivalues are positive
for the products and negative for the reactants (initial substances).

Example

Write the neutralization of sulphuric acid by sodium hydroxide in the form of equation (5.1), and

in that of equation (5.2).