Video 9.1

Rate: A measure of the speed of any change.

Collision Theory: When two chemicals react, their molecules have to collide with each other with proper energy and orientation.

When temperature increases, the molecules move ___________ and collide ________.

So the rate of reaction ____________, or the reaction moves _____________.

Temperature

faster

moreincreases

faster

When concentration increases, the molecules collide ________.

So the rate of reaction ____________, or the reaction moves _____________.

Concentration

more

increasesfaster

When the surface area increases, the molecules collide ________.

So the rate of reaction ____________, or the reaction moves _____________.

Surface Area

more

increases

faster

When catalysts are added, the make the reaction ___________ and collide ________.

So the rate of reaction ___________.

Catalysts

fastermore

increases

Ionic substances react faster than covalent substances because the easily break

into ions when you dissolve them.

Nature of Reactants

When the pressure on a gas increases, the gas has __________ volume. Therefore, there are _________ collisions and the rate __________, or moves _____________.

Pressure

less

moreincreases

faster

Video 9.2

If heat is absorbed, the reaction is endothermic and the enthalpy increases (+).

If heat is released the reaction is exothermic and the enthalpy decreases (-).

Enthalpy: Heat

Reactions with negative enthalpy values are exothermic. The heat can be added to the reaction on the products side.

CH4 + 2O2 CO2 + 2H2O + 890.4KJ

Reactions with positive enthalpy values are endothermic. The heat can be added to the reaction on the reactant side.

182.6KJ + N2 + O2 2 NO

Reference Table I

• More stable

• Spontaneous

• The reactants in the reaction have more energy than the products.

Exothermic Reactions

1. Endothermic or exothermic?a. Formation of NO2

b. Synthesis of C2H6

c. Formation of CO2 from elements

d. Dissolving LiBr

2. Which is more stable?a. H2O(g) or H2O(l)

b. C2H2 or Al2O3

Review with Table I

ENDO

EXO

EXO

EXO

H2O(l)

Al2O3

Use mole ratios to calculate how much heat is evolved in a reaction:

89.3KJ + C + 2S CS2

1.How much heat is absorbed when 5.00 moles of C are used?

2.How much heat is needed to produce 3.00 moles of CS2?

Enthalpy in reactions

447KJ

268KJ

5(89.3) =

3(89.3) =

Video 9.3

Activation EnergyThere is a minimum amount of energy required for reaction: the activation energy, Ea.

Just as a ball cannot get over a hill if it does not roll up the hill with enough energy, a reaction cannot occur unless the molecules possess sufficient energy to get over the activation energy barrier.

A + B C + D

Exothermic Reaction Endothermic Reaction

The activation energy (Ea) is the minimum amount of energy required to initiate a chemical reaction.

13.4

The activated complex is the highest part of the graph where the reaction can go to completion or revert back to reactants.

Enthalpy, or heat, can be measured on the graph by subtracting reactants from products.

Energy Diagrams

Exothermic Endothermic

CatalystsCatalysts increase the rate of a reaction by decreasing the activation energy of the reaction.

Catalysts change the mechanism by which the process occurs.

Video 9.4

The more disorder, the higher the entropy.

The entropy of a gas is _______ than a liquid or solid.

The more substances, the __________ the entropy.

As temperature increases, entropy _____________.

Entropy = Disorder

More

higher

increases

If a reaction is exothermic and is disorderly, the reaction will be

spontaneous.

Think about

Spontaneous

combustion!

Spontaneous Reactions

1. Contrast enthalpy and entropy.

2. As a system becomes more random, entropy _________.

3. What phase changes increase entropy?

4. On a heating curve, which point has the most entropy?

Review

Video 9.5

Equilibrium

Equilibrium

N2O4 NO2

N2 + 3H2 2NH3

A reaction at equilibrium means the forward and reverse reaction occur at the same rate.

If any change happens, the equilibrium will shift in a direction that reduces that change.

Le Châtelier’s Principle

N2O4 NO2

If a substance is taken, the reaction will shift toward that substance to restore equilibrium.

If a substance is added, the reaction will shift away from that substance to restore equilibrium.

2H2 + O2 2H2O

The Effects of Changes in Concentration

Concentration

The Effect of Changes in Temperature

Endothermic Reactants + Heat Products

Exothermic Reactants Heat + Products

Heat is considered a reactant and product

An increase in volume decreases the pressure and causes a shift that favors more moles of gas

A decrease in volume increases the pressure and causes a shift that favors less moles of gas

N2O4(g) 2NO2(g)

The Effects of Changes in Volume

Volume/Pressure 2Red 1Gray

CatalystsCatalysts increase the rate of both the forward and reverse reactions.

Equilibrium is achieved faster, but the reactants and products do not change.

1. Consider the following equation:N2 + 3H2 2NH3 + 92KJ

Predict how the H2 will be affected by:

a. Ammonia being added

b. Nitrogen being added

c. Heat being added

d. Pressure decreasing

e. Ammonia being removed

f. Nitrogen being removed

g. Decreasing the volume

LeChatelier Problems

increasesdecreases

increases

increases

decreases

increases

decreases