PHYSICAL CHEMISTRY IN BRIEF

CHAP. 3: FUNDAMENTALS OF THERMODYNAMICS [CONTENTS] 71

The change in the Gibbs energy ∆Gduring a reversible isothermal and isobaric process is
equal to other than volume work,Wother, supplied to the system

∆G=Wother≡W−Wvol=W+p∆V , [T, p, reversible process]. (3.15)

Example

The change in the Gibbs energy during the oxidation of one mole of glucose, according to the

reaction

C 6 H 12 O 6 + 6 O 2 = 6 CO 2 + 6 H 2 O

is∆G=−2870 kJ mol−^1. How high can a person weighing 75 kg climb if he or she has eaten

one mole (186 g) of glucose? The biological efficiency is 25%.

Solution

In our example,Wotheris equal to mechanical work needed for lifting a load to a heighth

Wother=−mgh ,

wheremis the mass of the load andgis the gravitational acceleration. If we project a human

body as an isothermal and isobaric system in which reversible processes occur and which does

not perform any volume work, then equation (3.15) leads us to

∆G=−mgh −→ h=−

∆G

mg

=

−2 870 000

75 × 9. 8

= 3905 m.

We obtain the real height by multiplying the result by the biological efficiency,

3905 × 0 .25 = 976m.

.