6o 



BIOLOGICAL CHEMISTRY 



INFLUENCE OF TEMPERATURE 



The rate of most chemical reactions increases with rise of 

 temperature and the increase is an exponential function of the 

 temperature ; that is if we plot the rate of reaction against the 

 temperature we obtain a curve as shown in the diagram which 

 is convex towards the axis of the ordinates. This means 

 that the rate of reaction becomes of explosive rapidity at 

 high temperatures. The usual way to express the increase in 

 rate is the temperature coefficient of Arrhenius which signifies 

 the ratio of the two rates at temperatures ten degrees Centi- 

 grade apart.* Most chemical reactions have a coefficient 

 between two and three at moderate temperatures and physical 



20 30 



TEMPERATURE 



FIG. 12. Diagram illustrating effect of temperature on rate of 

 reaction. 



A reaction with the rate of i at ioC. and a temperature coefficient of 2 (continuous line) 

 shows a rate of 2 at 20, 4 at 30, and 8 at 40, whilst with a temperature coefficient of 3 

 (interrupted line) the rates are 3 at 20, 9 at 30 and would reach 27 at 40. 



processes have a coefficient outside this range. The diagram 

 gives two curves showing temperature coefficients of two and 

 of three. 



* J. H. van't Hofif, Studies in Chemical Dynamics, translated by 

 T. Ewan. Williams and Norgate, 1896, p. 125. 



