Chemistry chapter 10

Reacting molecules requirements to form products

must collide, have a minimum amount of energy, and have the proper orientation to form products

activation energies

reactions with low activation energies go faster than reaction with high activation energies

Factors that affect the rate of reaction

changes in temperature, changes in reaction concentration, and adding a catalyst

Temp effect on rate of reaction

As temp increases so does the rate of reaction and as temp decreases so does the rate of reaction.

Higher temp effect of rate of reaction

Makes molecules moves faster, collide more often, and collide with more energy

rate of reaction: concentration

when there are more reacting molecules, more collisions that form products can occur, and the reaction goes faster

Catalysts effect of rate of reaction

Adding a catalyst speeds up the rate of the reaction and provides a path with a lower activation energy

table of factors that increase the reaction rates

increasing temp, increasing reactant concentration, and adding a catalyst

A. increases

B. decreases

C. Increases

D. decreases

Chemical equilibrium equation

Where is the product in a equilibrium equation

the product is where the arrow points

reversible reaction

when a reaction can proceed in both a forward and a reverse direction

When is a reversible reaction at equilibrium

when the rate of the forward reaction becomes equal to the rate of the reverse reaction.

What happens to the reversible reaction once it reaches equilibrium

when equilibrium is reached there are no further changes in the concentrations of the reactant and products. The concentration are not equal.

At equilibrium what are the rates and concentrations

At equilibrium the rates should be equal but the concentrations should not be equal to one another.

What is the equilibrium constant expression

K_c

What formula do you use to find the equilibrium constant expression K_c

what do the brackets and the a,b,c, and d superscripts indicate in the K_c formula

The brakes indicate the M, moles/liter, of each substance and the a,b,c,and d superscripts are the coefficients of the reaction.

How to find K_c for both forward and reverse

K_c= [products] / [reactions]

what would be the forward reaction for the following

What would be the reverse reaction for the following

[C]^c [D]^d

K_c= [A]^a [B]^b

Writing a K_c Expression

when writing the K_c expression how do you know if it wants a forward or reverse reaction.

when it ask for the K_c expression for the following reaction at equilibrium and it does not say Reverse then the reaction is forward

Heterogeneous Equilibrium

• sold and/ or liquid states may be part of a reaction

• the concentration of solids and/ or liquids is constant

• the K_c expression is written with only (g) or (aq)

Example of a heterogeneous equilibrium K_c expression

K_c = [CO₂][H₂O]

what to do first before setting up the K_c expression?

balance the reaction first, find if it is forward or reverse, and then remove all solids and liquids from the reaction.

4) [O₂]³

1) 0.26

Large K_c

reactions with a large K_c have large amounts of products produced

(more products then reactants)

Small K_c

reactions with a small K_c have an equilibrium mixture with a low concentration of products and a high concentration of reactants.

(more reactant then products)

Equilibrium with a large and small K_c rules

• If K_c is greater then one then the products are favored K_c>1 large

• If K_c is less then one then the reactants are favored K_c > 1 Small

• If K_c is greater then 1 the exponent is positive, Large

• If K_c is less then 1 then the exponent is negative Ex: 2 × 10^-9. Small

• If K_c equals 1 then nothing is favored

A. Product

B. Reactants

cross multiply

0.24 M PCl₅

cross multiply

0.78 M Brff

What happens when you add a reactant to a equilibrium reaction

It shifts to the opposite side (product) and the rate increases forward to make more products

Effects of adding product

It shift to the opposite side (reactant side) and the rate of the reverse reaction increases to form more reactants.

what happens when you remove a reactant

It shift towards the reactants and increases the rate of the reverse reaction to form more reactants

What happens when you remove a product?

It shifts toward the product side and the rate of the forward reaction increases to form more product

solid does not count

A. to the reactants

B. no change

C. to products

D. to products

Effect of a catalyst on equilibrium

speeds up the reaction by lowering the activation energy, thus increasing the rate of the forward and reverse reactions. Adding a catalyst does not change the equilibrium mixture

Effect of decreasing the volume

it shifts in the direction of the smaller number of moles and increases the concentration of the gases

effect of increasing the volume

it shift to the larger number of moles and decreases the concentration of the gases

Heat and endothermic reactions (heat on the left)

• If you decrease temperature it shifts top the left (reactants side)

• If you increase temperature It shifts to the right (product side)

Heat and Exothermic reactions (heat is on the right)

• If temperature decreases then it shifts to the right (product side)

• If temperature increases then it shifts to the left (reactants)

A. toward products

B. toward reactants