The area of chemistry that concerns reaction rates (how fast a reaction occurs)

Unit 11.1

Chemical Kinetics

Collision Model Key Idea: Molecules must collide to react.

However, only a small fraction of collisions produces a reaction. Why?

Collision Model

Collisions must have sufficient energy to produce the reaction (must equal or exceed the activation energy).

Colliding particles must be correctly oriented to one another in order to produce a reaction.

1.

2.

Endothermic Reactions

Exothermic Reactions

Factors Affecting Rate

Increasing temperature always increases the rate of a reaction.

Particles collide more frequently

Particles collide more energetically

Increasing surface area increases the rate of a reaction

Increasing Concentration (amount of reactants) USUALLY increases the rate of a reaction

Presence of Catalysts, which lower the activation energy by providing alternate pathways

Catalysis •Catalyst: A substance that speeds up a reaction without being consumed

•Enzyme: A large molecule (usually a protein) that catalyzes biological reactions.

Lowering of Activation Energy by a Catalyst

Unit 11.2

Boiling points and phase diagrams

Chemical Equilibrium

Reversible Reactions:

A chemical reaction in which the products can react to re-form the reactants

Chemical Equilibrium:

When the rate of the forward reaction equals the rate of the reverse reaction and the concentration of products and reactants remains unchanged

2HgO(s) 2Hg(l) + O2(g)

Arrows going both directions ( ) indicates equilibrium in a chemical equation

Vapor pressure

• Vapor pressure of a liquid: pressure exerted by the liquid’s vapor at equilibrium

liquid + heat ↔ vapor

Higher temperatures = higher vapor pressures

Strong intermolecular forces = lower vapor pressures

Vapor pressures of different compounds

Boiling • Boiling occurs when a liquid’s vapor pressure = atmospheric

pressure.

• As the temp. of a liquid increases, its vapor pressure increases until it equals the outside pressure, this is when boiling starts

• In the mountains there is less atmospheric pressure so liquids will boil at a lower temp.

• Pressure cookers will increase the temp. at which liquids boil by increasing the outside pressure. Food can cook faster because the water is at a hotter temperature when boiling.

• Normal boiling point is the temp. liquids boil at sea level.

Effect of Pressure on Boiling Point

Phase Diagram Represents phases as a function of temperature and pressure.

Critical temperature: temperature above which the vapor can not be liquefied.

Critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm).

Triple point: where all three phases are in equilibrium

Phase changes by Name

Water

Carbon dioxide Phase

Diagram for Carbon dioxide

Carbon Phase

Diagram for Carbon

Unit 11.3

Le Chatlier’s principle

Chemical Equilibrium

Reversible Reactions:

A chemical reaction in which the products can react to re-form the reactants

Chemical Equilibrium:

When the rate of the forward reaction equals the rate of the reverse reaction and the concentration of products and reactants remains unchanged

2HgO(s) 2Hg(l) + O2(g)

Arrows going both directions ( ) indicates equilibrium in a chemical equation

LeChatelier’s Principle

When a system at

equilibrium is placed under

stress, the system will

undergo a change in such

a way as to relieve that

stress.

Henry Le Chatelier

When you take something away from a system at equilibrium, the system shifts in such a way as to replace what you’ve taken away.

Le Chatelier Translated:

When you add something to a system at equilibrium, the system shifts in such a way as to use up what you’ve added.

LeChatelier Example #1

A closed container of ice and water at equilibrium. The temperature is raised.

Ice + Energy Water

The equilibrium of the system shifts to the _______ to use up the added energy.

right

LeChatelier Example #2

A closed container of N2O4 and NO2 at equilibrium. NO2 is added to the container.

N2O4 (g) + Energy 2 NO2 (g)

The equilibrium of the system shifts to the _______ to use up the added NO2. left

LeChatelier Example #3 A closed container of water and its vapor at equilibrium. Vapor is removed from the system.

water + Energy vapor

The equilibrium of the system shifts to the _______ to replace the vapor. right

Lowering of Activation Energy by a Catalyst