Chemistry, Third edition

SPECIAL KINDS OF STANDARD ENTHALPY CHANGE

Special kinds of standard enthalpy

change

Some examples of special standard enthalpy changes are listed in Table 13.1.

13.4

225

Determining enthalpy changes 2

50.0 cm^3 of 1.00 mol dm^3 HCl and 50.0 cm^3 of 2.00 mol dm^3 NaOH (both at an initial tem-

perature of 17.40 °C) were rapidly mixed in a vacuum flask and the maximum temperature

recorded electronically as 23.60 °C. Write down an ionic equation for this reaction and esti-

mate the enthalpy change of reaction per mol of water formed. The literature value for H^ —is

57.3 kJ mol^1.

Exercise 13F

Table 13.1Examples of special standard enthalpy changes

Name Symbol Description Example of process

Enthalpy of H^ —f one mole of compound K(s) ^1 ⁄ 2 Cl 2 (g)KCl(s)
formation made from its elements

Enthalpy of H^ —c one mole of a fuel CH 4 (g) 202 (g)

combustion burned in excess oxygen CO 2 (g)2H 2 O(l)

Lattice enthalpy H^ —L one mole of a crystal K,Cl(s)K(g)Cl(g)
completely separated into
isolated particles in the
gas phase

Enthalpy of H^ —N one mole of water formed by CH 3 COOH(aq)NaOH(aq)
neutralization the neutralization of an acid CH 3 COONa(aq)H 2 O(l)
by a base

Bond dissociation H^ —c(A–B) one mole of bonds broken: HCl(g) H(g)Cl(g)
enthalpy(of a all species in the gas phase
specific bond A–B)

Ionization energy H^ —ionorI one mole of atoms (or Na(g) Na(g)e

(also known as molecules) ionized: all (first ionization energy)
ionization enthalpy) species in the gas phase

Enthalpy of electron H^ —eg one mole of anions being F(g) eF(g)
gain(H—^ egis called formed: all species in the

electron affinity) gas phase

Enthalpy of H^ —vap one mole of vapour being H 2 O(l)H 2 O(g)
vaporization formed from liquid without a
change in temperature

Enthalpy of fusion H^ —fus one mole of liquid being H 2 O(s)H 2 O(l)
formed from the solid without
a change in temperature

Enthalpy of H^ —atom one mole of substance broken Ca(s)Ca(g)

atomization up into its isolated atoms in
the gas phase