Figure. A schematic diagram showing the effect of the temperature on the stability of an enzyme catalysed reaction. The curves show the percentage activity remaining as the incubation period increases. From the top they represent equal increases in the incubation temperature (50º C, 55º C, 60º C, 65º C and 70º C).
The is a unitless number, that summarizes the effect of raising temperature 10º C on the rate of a chemical reaction. A of 2.0 suggests that raising the temperature of a system by 10º C will effectively double the rate of the reaction. This value would be expected for most chemical reactions occurring within normal physiological temperatures.
Mathematically, can be represented by the following expression:
t2 = higher temperature k2 = rate at t2
t1 = lower temperature k1 = rate at t1
Ussualy the temperature difference is about 10º C, then you can simplify the equation
Edit: You can easly calculate k form Arrhenius equation
where k is the kinetic rate constant for the reaction, A is the Arrhenius constant, also known as the frequency factor, is the standard free energy of activation (kJ M-1) which depends on entropic and enthalpic factors, R is the gas law constant and T is the absolute temperature.