# Talk:Reaction rate/April 1 cleanup

There are many factors that affect on the rate of reaction:

A pair of forward and reverse reactions may define an equilibrium process. For example:

a + b <=> x + y

The Reaction rate expression for the above reactions (assuming they each are elementary) can be expressed:

-r = k1 [a][b] - k2 [x][y]

, where k1 is rate constant for the reaction which consumes a and b. "k2" is rate constant for the backwards reaction, which consumes x and y and which products are a and b.

The constants k1 and k2 are related to the equilibrium constant for the reaction (K) by the following relationship:

K = k1/k2

The constant K can also be expressed:

K = [a][b]/[x][y] = k1/k2

Each reaction rate constant k(i.e., k1 and k2) has temperature dependedancy, which is usually presented as:

k = A*exp(Ea/RT)

where A is the frequency factor and Ea is the reaction's activation energy. T is the absolute temperature and R is the ideal gas constant. Ea is strictly non-negative, and so reaction rates are non-decreasing with temperature. The formula shown above is known as the Arrhenius equation. The values for A and Ea are dependent on the reaction (so, for example, they may differ between k1 and k2). There are also more complex possible, which describe temperature dependance of rate constant.

The equilibrium constant K is dependent on temperature. This equation is known as the van't Hoff equation.