Reaction rate

The reaction rate of a chemical reaction, that is, the speed of production of products or reactants, may generally be expressed as rate = k [a]^x where [a] is the molar concentration of reactant (there may be several), x is the order for that reactant, and k is a constant. Order establishes the mathematical relation of concentration to rate; eg. for an order of 2, if the concentration doubles, the rate quadruples.

Rate is often expressed in moles per liter-second. There are many factors that affect on the rate of reaction:

Reaction rate for the chemical reaction a -> products

can be expressed:

-r = k [a]

Rate r is negative, because reaction consumes A. Usually reactions are equilibrium reactions. For example: a + b <=> x + y Reaction rate equation for above reaction 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.

There is correlation between k1 and k2.

K = k1/k2

K is equilirium constant for the reaction.

Constant K can also be expressed:

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

Reaction rate constant k 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. Formula shown above is known as Arrhenius equation. There are also other possible equations, which describe temperature dependance of rate constant.

Also Equilibrium constant K is dependent of temperature. This equation is known as van't Hoffs equation.