H

Haber, Fritz (1868–1934) German

chemist who worked at the Karl-

sruhe Technical Institute, where he

perfected the *Haber process for

making ammonia in 1908. As a Jew,

he left Germany in 1933 to go into

exile in Britain, working in Cam-

bridge at the Cavendish Laboratory.

For his Haber process, he was

awarded the 1918 Nobel Prize for

chemistry.

Haber process An industrial

process for producing ammonia by

reaction of nitrogen with hydrogen:

N 2 + 3H 2 ˆ2NH 3

The reaction is reversible and

exothermic, so that a high yield of

ammonia is favoured by low temper-

ature (see le chatelier’s principle).

However, the rate of reaction would

be too slow for equilibrium to be

reached at normal temperatures, so

an optimum temperature of about

450 °C is used, with a catalyst of iron

containing potassium and alu-

minium oxide promoters. The higher

the pressure the greater the yield, al-

though there are technical difÜcul-

ties in using very high pressures. A

pressure of about 250 atmospheres is

commonly employed.

The process is of immense impor-

tance for theÜxation of nitrogen for

fertilizers. It was developed in 1908

by Fritz *Haber and was developed

for industrial use by Carl Bosch

(1874–1940), hence the alternative

name Haber–Bosch process. The ni-

trogen is obtained from liquid air.

Formerly, the hydrogen was from

*water gas and the water–gas shift

reaction (the Bosch process) but now

the raw material (called synthesis

gas) is obtained by steam *reforming

natural gas.

habitSee crystal.

haem(heme)An iron-containing

molecule that binds with proteins as

C

H

CH CH

C

H

N N

N N

CH 2

CH 2

3 CH

3 CH CH 3

CH 3

HOOC COOH

Fe

Haem