Reaction Rates Reactions over time -Different reactions have different durations (can be measured over time) -TNT almost instantly, leaves changing color happens gradually -A reaction rate tells you how fast the reaction is going

Factors Affecting Reaction Rates Depends how often the particles collide If the collisions occur frequently, then the reaction rate increases Less frequent, it decreases Factors that affect the reaction rate are temperature, surface area, concentration, stirring, and catalysts

Temperature What happens if you increase the heat under the pan????

Temperature An increase in temperature will increase the reaction rate, while a decrease in temperature will decrease the reaction rate Increasing the temperature of a substance causes the particles to move faster Particles that move faster are more likely to collide and react

Surface Area The cause of the fire was a combustion reaction between grain dust (suspended in air) and oxygen -The rate of combustion was rapid due to the small particle size of the grain dust

Surface Area The smaller the particle size of a given mass, the larger is its surface area. An increase in surface area increases the exposure of reactants to one another With more collisions, more particles will react

Stirring You can increase the exposure of reactants to each other -Example: When you wash your clothes in a washing machine, particles of detergent react with particles of the stains on your clothes

Stirring A washing machine speeds up the reaction by stirring the contents back and forth Collisions between the particles of the reactants are more likely to react Stirring increases the reaction rate

Concentration Refers to the number of particles in a given volume Reaction rate is faster if there are more chances for particles to collide and react

Concentration For gases, concentration changes with pressure The greater the pressure of a gaseous reactant, the greater is its concentration, and the faster is the reaction rate

Catalysts Is a substance that affects the reaction rate without being used up in the reaction Chemists use it to speed up a reaction or enable a reaction to occur at a lower temperature Neither a reactant or product Can be used more than once Provides a surface on which the reacting particles come together (lowers the energy barrier)