NOTES 17.1 CHEMISTRY

 

How Chemical Reactions Occur

COLLISION MODEL molecules must collide in order to react - a reaction proceeds faster if the

concentrations for the reacting molecules are increased

- reactions go faster at higher temperatures

CONDITIONS THAT AFFECT REACTION RATES

A minimum energy called activation energy (Ea) is needed for a reaction to occur

If a given collision possesses an energy greater than Ea, that collision can result in a reaction.

If a collision has energy less than Ea, the molecules will bounce apart unchanged

At higher temperatures the average collision is more energetic

CONDITIONS THAT AFFECT REACTION RATES

A catalyst can speed up a reaction without being consumed in the overall reaction

Enzymes are catalysts in our bodies that help speed up complicated reactions that would be too slow to sustain life at normal body temp.

A catalyst works because it provides a new pathway for the reaction- a pathway that has a lower activation energy than the original pathway (more collisions will have enough energy to allow a reaction)

HETEROGENEOUS REACTIONS

Homogeneous reaction- involves reactants and products in one phase of matter

Heterogeneous reaction- involves reactants and products in two phases of matter

-The speed of a reaction depends on the surface area available

-surface area effects the explosive combustion of grain dust

 

THE EQUILIBRIUM CONDITION

Chemists define equilibrium as the exact balancing of two processes, one of which is the opposite of the other. ( page 601)

The equilibrium state occurs when the rate of evaporation exactly equals the rate of condensation

There are many chemical reactions that “stop” far short of completion when they are allowed to take place in a closed container.

 

THE EQUILIBRIUM CONDITION

Chemical equilibrium is a dynamic state where the concentrations of all reactants and products remain constant, as long as the conditions are not changed.

Chemical reactions that are reversible, they can occur in either direction, are indicated by double arrows. Pg 602

CHEMICAL EQUILIBRIUMEquilibrium is not static but is a highly

dynamic situation- it may appear everything has stopped but on the molecular level there is frantic activity