Page 30 - Color Atlas of Biochemistry

Physical Chemistry 21

A. Heat of reaction and calorimetry

Thermometer Ignition wire
to start the reaction
6 6
5 5
4 4
3 3
2 1 2 1
Temperature 1 1
2 3 2 3
insulation 4 5 Water Combustion 4 5 Water Water
6 6
heated
Pressurized O 2 CO 2
metal
container An enthalpy of H O
2
1kJ warms 1 l of water
Sample by 0.24 ºC
Stirrer
B. Enthalpy and entropy

∆H: change ∆G = ∆H - T · ∆S ∆S: change of
of enthalpy, entropy, i.e.
heat exchange degree of order
Gibbs-Helmholtz equation

1 mol H 2 1 mol NaCl
1/2 mol O 2 (crystalline)

Low degree High degree
of order of order

System re- System
leases heat, absorbs
∆H <0 heat,
(exothermic) ∆H > 0
(endothermic)

1 mol H O 1 mol Na
2
(liquid) 1 mol Cl

Lower
Higher degree degree
of order, of order
∆S < 0 ∆S > 0

∆H = - 287 kJ · mol -1 ∆H = +3.8 kJ · mol -1
-T · ∆S = +49 kJ · mol -1 -T · ∆S = - 12.8 kJ · mol -1

∆G = - 238 kJ · mol -1 ∆G = - 9.0 kJ · mol -1

-200 -100 0 +100 +200 -12 -8 -4 0 +4 +8 +12
Energy Energy

1. “Knall-gas” reaction 2. Dissolution of NaCl in water

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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