Chem Unit Four (Ch7&8)

Chemical Kinetics

The study of reaction rates

Rate of Reaction

The change in concentration of a reactant (or product) per unit of time

(Delta Concentration/Delta Time)

What is the equation for Rate of Reaction

Decreases

As times goes on, reactant gets used up and the Rate of Reaction _________

1. Molecular Collisions

2. Activation energy

3. Nature of the reactants

4. Concentration of the reactants

5. Temperature

6. Presence of a catalyst

What are the 6 factors affecting Rate of Reaction

1. Collisions must have high enough energy to break bonds

2. Orientation of colliding particles must allow for formation of any new bonds needed to produce products

What are the two requirements for an Effective Collision

Takes

Breaking bonds _____ energy

Releases

Forming Bonds ______ energy

Exothermic

If the energy in the reaction released was greater, it is an _______ reaction

Endothermic

If the energy in the reaction required was greater, it is an _______ reaction

Activation Energy

The minimum energy required to cause the reaction

exothermic

If the energy of the products is lower than the energy of the reactants, it is a _______ reaction.

Endothermic

If the energy of products is higher than the energy of the reactants, it is a _________ reaction

Reactions between ions in aqueous solution

• Generally very fast

• Activation energies are very low

• No covalent bonds that need to be broken

Reactions between covalent compounds

• Generally slower

• Doesn’t matter if solvent is water or something else

• Activation energies are higher

Concentration and Reaction Rate

For many reactions, there is a direct relationship between ______ and ________

Collisions

Higher concentration = More ________

increases

For virtually all reactions, reaction rate ________ as temperature increases.

Catalyst

A substance that:

• Increases the rate of reaction

• Is NOT used up by the reaction (not a reactant or product)

• Allows the reaction to take a different pathway with a lower activation energy

Reversible Reaction

A reaction that proceeds in both the forward and reverse direction

Equilibrium

A dynamic state in which the rate of the forward reaction is equal to the rate of the reverse reaction

Le Chatelier’s Principle

When stress is applied to a chemical system at equilibrium, the position of the equilibrium shifts in the direction that will relieve the applied stress.

Use up more reactants and makes more products

When the equilibrium shifts right:

Use up more products and make more reactants

When the equilibrium shifts left:

K = [C]^c [D]^d / [A]^a [B]^b

What is the equilibrium constant equation?

The products are favored

If K (equilibrium constant) is greater than 1:

The reactants are favored

If K (equilibrium constant) is less than 1:

Neither the reactants or the products are favored

If K (equilibrium constant) is equal to 1: