Heat - IB Chem 1 Unit 7

Four factors that affect reaction rates

• Temperature

• Concentration

• Surface Area

• Catalysts

Three requirements according to collision theory for a reaction to occur particles must

• Proper orientation

• Sufficient Energy

• Effective Collisions

Increasing temperature…

Increases:

• avg. kinetic energy

• frequency of collisions

• energy of collisions

Increasing concentration…

Increases:

• number of particles per volume

• frequency of collisions

Increasing surface area…

Increases:

• Exposed particles in a solid state

• Frequency of collisions

Adding a catalyst…

• Changes mechanism of reaction

• Decreases activation energy

• Makes more collisions effective

What must a catalyst be?

It must remain chemically unchanged at the end of the reaction.

Endothermic reactions

• Products less stable

• H>0

• Bonds in reactants stronger than bonds in products

Exothermic reactions

• Products more stable

• H<0

• Bonds in products stronger than bonds in reactants

Activation energy

Energy it takes to break existing bonds

What do breaking bonds do?

Breaking bonds absorb energy

Solid →Liquid

Melting

Solid → Gas

Subliming

Liquid → Gas

Boiling

Gas → Liquid

Condensing

Gas → Solid

Deposition

Liquid → Solid

Freezing