Controlling Chemical Reactions Science 10 Chemical Reactions 4

Controlling Chemical Reactions Science 10: Chemical Reactions 4

Controlling Chemical Reactions § All reactions occur at different speeds § There are many factors that influence how fast or how slow a reaction will go § Reaction Rate: the speed at which a reaction occurs

Kinetic Molecular Theory § States that particles are constantly moving and that they are more and more quickly at a higher temperature § As particles or molecules move about they hit or collide with each other § Not all collisions result in a reaction taking place § The faster the molecular motion the greater the chance of the collisions having enough energy to result in a reaction

Collision Model § States that the rate of reaction is affected by the number of collisions of the reactant molecules § Most collisions just result in molecules bouncing off of each other with no change § Only a small fraction of collisions are effective: they cause chemical bond to break and reform into new molecules § Two ways to increase the rate of reaction: § Increase the number of collisions that are effective

Temperature § Temperature is the most important factor § Even a small change in temperature can have a drastic effect on the rate of reaction § As temperature increases, the speed of molecules increase § The faster the molecules move, the greater the chance of an effective collision § As temperature decreases, the result is a decrease in reaction rate

Concentration § When the number of reactants are increased in an contained area the rate of reaction increases § The rate of reaction increases because as the concentration of the reactants increases the chance of reactants colliding also increases § Decreasing the concentration has the opposite effect

Surface Area § Surface area is the amount of area of a sample of matter that is visible or able to react § The surface area can be increased by decreasing the sizes of the pieces of the reactants (breaking a large piece into many small pieces) § Increasing the surface area increases the number of particles colliding and therefore increases the rate of reaction § Decreasing the surface area has the opposite effect

Catalysts § A catalyst is a substance that increases the rate of reaction without being consumed by the reaction § Catalysts are very important for industrial processes including oil refining § More importantly, they are part of biological processes; these catalysts are called enzymes § Catalysts lower the amount of energy needed in order for a reaction to take place