Rates+of+reactions

Different chemical reactions occur at different rates, some are slow and some are fast. The rate of a reaction is the measure of the change in the concentration of the products/reactants per unit time. Thus the rate for a reaction can be expressed as:

 OR 

Where **[P]** is the concentration of the products and **[R]** is the concentration of the reactants.

The units for rate of a reaction is mol dm -3 s -1  (mol per dm 3  per second)

As can be seen in the equation the rate of the reaction shows how the concentration of the products or reactants changes overtime. Usually any measurable property of the reactants/products (such as mass, volume, pH) that changes as the reaction progresses can be used to calculated the rate of the reaction.

As a reaction progresses, the concentration of products increases over time. Thus a graph can be drawn to show how the concentration increases with time:



The graph shows how the concentration of the products increases with time, as the reactants are used up. //The gradient of the graph at any one point shows the rate of the reaction at that point.//

Usually the rate of a reaction decreases with time since the concentration of reactants decreases with time, so there is less of them available to react and form the products.


 * By the end of this lesson you should be able to: **
 * ** Define the term "rate of a reaction". **
 * ** know that to measure the rate of a reaction we look at how a measurable property of a reactant or a product changes with time. **
 * ** Be familiar with the graph of concentration versus time for the products/reactants of a reaction. **


 * media type="googleplusone" key="" width="360" height="18" ||
 * media type="facebooklike" key="http%3A%2F%2Fibchem4u.wikispaces.com%2FRates%20of%20reactions" width="360" height="74" ||