Rates and Orders

Definition: is the change in concentration of a reactant or product per unit time

Equation= change in concentration of reactan or product / time taken for change to take place

As a reaction proceeds, the concentrations of the reactants decrease:

• fewer collisions take place per second between reactant particles
• the rate of the reaction slows down.

Initial rate: the change in concentration of a reactant, or product, per unit time at the start of the reaction when t=0

Measuring rates

The rate of the reaction can be determined by measuring the concentrations at time intervals during the course of a reaction. Results are plotted on a concentration-time graph

• at any instant of time, the rate is equal to the slope of the graph
• the slope is measured by drawing a tangent to the curve at this time
• the gradient of the tangent is then calculated .

for reactions involving acids or bases, measure:

• pH changes via titrations or by using a pH meter

For reactions that produce gases, measure:

• the change in volume or pressure, or the loss in mass of reactants

For reactions that produce visual changes, observe:

• the formation of a precipitate, or a colour change