Fritz Haber

Who he was

Fritz Haber was a German physical chemist, born in Breslau in 1868. He did most of his celebrated work at the Technical University of Karlsruhe and then led one of the world’s leading research institutes in Berlin. His life is one of the most debated in the history of chemistry: the same scientist helped to feed the world and to bring poison gas to the battlefield.

Key contributions

Ammonia from air. Around 1900, farming depended on natural nitrates, mostly mined in Chile, and these were running out. The air is about 78 % nitrogen, but the $\ce{N#N}$ triple bond makes nitrogen gas very unreactive. Haber studied the equilibrium

\begin{aligned} &\ce{N2(g) + 3H2(g) <=> 2NH3(g)}\\ &\Delta H = -92\ \text{kJ mol}^{-1} \end{aligned}

and found conditions that give a useful yield at a useful rate: high pressure (about 200 atm), a moderate temperature (about 500 °C) and an iron or osmium catalyst, with the ammonia removed and the unreacted gases recycled. In 1909 his tabletop apparatus produced a steady stream of liquid ammonia, and Carl Bosch of BASF scaled the process up to an industrial plant by 1913.

Key idea

The Haber process is Le Chatelier’s principle at work: high pressure favours the side with fewer gas molecules (2 instead of 4), while the temperature is a compromise between a good yield (favoured by low temperature, since the reaction is exothermic) and a fast rate (favoured by high temperature).

The Born–Haber cycle. With Max Born, he showed in 1919 how to calculate the lattice energy of an ionic solid from measurable steps, an application of Hess’s law still taught today.

Poison gas

During the First World War, Haber put his institute at the service of the German army and directed the first large chlorine gas attack, at Ypres in April 1915. Thousands of soldiers were killed or injured. His wife, Clara Immerwahr, one of the first women to earn a doctorate in chemistry in Germany, died by suicide later that year. When he received the Nobel Prize in 1919, several scientists protested.

Prizes and legacy

Haber received the 1918 Nobel Prize in Chemistry “for the synthesis of ammonia from its elements”. Fertilizers made from Haber–Bosch ammonia now support the food supply of roughly half the world’s population. In 1933, although he had converted to Christianity, he was targeted by the Nazi government’s anti-Jewish laws; he resigned rather than dismiss his Jewish colleagues, and died in exile the next year. His story is often used to discuss the responsibility of scientists for how their discoveries are used.

Connections to your lessons

The Haber process is the classic example in the lessons on chemical equilibrium and Le Chatelier’s principle, and the Born–Haber cycle extends the lesson on Hess’s law.

Timeline

1868Born in Breslau to a Jewish merchant family.

1894Joins the Technical University of Karlsruhe, where he works for 17 years on electrochemistry and gas reactions.

1909Demonstrates a working laboratory apparatus that makes ammonia from nitrogen and hydrogen over a catalyst at high pressure.

1911Becomes the first director of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin.

1913The chemical company BASF, with Carl Bosch, opens the first industrial ammonia plant based on his process.

1915Directs the first large chlorine gas attack, at Ypres in Belgium. His wife, the chemist Clara Immerwahr, dies the same year.

1919Receives the 1918 Nobel Prize in Chemistry; the award is controversial because of his wartime work. With Max Born, publishes the Born–Haber cycle.

1933Resigns as director in protest when the Nazi government orders the dismissal of Jewish staff, and leaves Germany.

1934Dies in Basel, Switzerland, on his way to a new post in Palestine.

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