Johannes Nicolaus was born on February 22, 1879, at Varde, Jutland. His mother died shortly after his birth and his father remarried. Brønsted's father was a civil engineer who worked for a corporation dedicated to drainage, irrigation, and planting in marshy. However, it was only 14 years old when his father also died.
After the loss of both parents, the young Brønsted and his sister moved to Copenhagen with their stepmother and Brønsted attended the Metropolitanskolen for three years. He passed his 'studentereksamen' (University entrance examination) in the summer of 1897.
Brønsted entered the Faculty of Chemical Engineering at the Technical University of Denmark in 1897. Two years later he received his degree, then left the Technical University and entered the Faculty of Natural Sciences at the University of Copenhagen, from which he obtained a Master of Science in chemistry in 1902. In 1908, he got a Ph.D. from the University of Copenhagen in 1908.
After a period of nonchemical research, Johannes Nicolaus Brønsted was appointed assistant of a chemical laboratory in 1905 at the University of Copenhagen, and from then on he was attached to the university, serving as professor of physical chemistry from 1908.
Since the conclusion of Julius Thomsen’s studies on thermochemistry in 1886, physical chemistry had been somewhat neglected in Denmark, although the work of Ostwald, Arrhenius, and Nernst was followed up in most other countries. Brønsted took over Thomsen’s idea of determining chemical affinity by measuring the maximum work of a chemical process, but instead of using calorimetric determinations, he used electromotive force measurements for galvanic cells, which give correct values at room temperature, whereas the calorimetric method gives values that are in error by an amount proportional to the entropy changes taking place for the process in the chemical reaction. He published the results in a series of thirteen monographs on chemical affinity (1906–1921).
Other aspects of physical chemistry aroused Brønsted’s interest after 1913: not only the determination of specific heats but also the determination of affinity constants, published in a series of studies on solubility (1921–1923) and on the specific interaction of ions (1921–1927). These studies evoked considerable interest among physical chemists, especially in the United States and in England, and from 1921 to about 1935 Brønsted’s laboratory was crowded with foreign guests desiring to study under his guidance. The poor laboratory conditions were considerably improved when the International Education Board offered to defray the expenses connected with the building of a new Institute of Physical Chemistry, provided the Danish government would take over the operation of the institute, which began operation in 1930. Famous among these studies is a paper, written with V. K. la Mer, on the relation between activity coefficients and the ionic strength of the solution, a relation derived theoretically at the same time by P. Debye and E. Hückel.
Other achievements, too, deserve to be mentioned: Brønsted’s definition of acids and bases (1923), simultaneously suggested in almost identical form by T. M. Lowry and in an extended version by G. N. Lewis; his studies on catalysis (1924–1933); and his work on the separation of isotopes of mercury and chlorine (1920–1922, 1929), done with G. von Hevesy.
In 1912 Brønsted published a short manual of physical chemistry, based on the thermodynamic cycle of Carnot. Before 1936, when a new edition had to be written, Brønsted had become convinced of the superiority of J. W. Gibbs’s approach to thermodynamics, and the new, substantially enlarged edition was based on Gibbs’s ideas.
Brønsted was convinced that sooner or later a war would explode, so he spent several hours a day listening to the news from England. The outbreak of the second world war strengthened his ties with England and its people. It also made him pay more attention to social issues, especially related to Schleswig.
Brønsted's opposition to the Nazis led to his election to the Danish parliament in 1947, but he was too ill to take his seat and died shortly after the election.
Brønsted was unhappy with the classical formulation of the laws of thermodynamics, according to which heat is not directly comparable to other forms of energy. To him, heat, like other forms of energy, can be considered as composed of a quantity factor (the entropy) and an intensity factor (the temperature). In this way it was possible to formulate the first law of thermodynamics as a work principle, whereas the second law was broadened to a heat-and-equivalence principle, including also irreversible reactions. A characteristic of this approach is that it relates thermodynamics to physical concepts rather than to mathematical complexities.
Brønsted’s formulations, especially his use of the principles “work” and “heat,” were not approved by the physicists, and angry discussions took place. He tried to concrete his principles in later works (1940, 1941, 1946), but no agreement had been reached by the time of his death.
In 1935 Brønsted was appointed a member of the Royal Society of London.
At the Polytechnic Institute Brønsted met Charlotte Louise Warberg, who in 1902 became one of the very first female engineers in Denmark. They were married in 1903 and moved into a flat at Forchhammersvej in Copenhagen. The couple had two children.
