Equilibrium systems (Chapter 7)

Reversible reaction

chemical reaction that occurs in both the forward and reverse direction

Forward reaction

read from left to right

Reverse reaction

right to left

equilibrium

A state of balance, when net concentrations remain constant

When solution has reached equilibrium rate fwd and rev are…

the same

Concentration at equilibrium are always

1. dynamic (in constant motion)

2. Reversible ( can be approached from either direction)

3. always in a closed system

Dynamic equilibrium

chemical systems at equilibrium that is changing at the molecular level but macroscopic properties remain constant

macroscopic properties

observable or measurable properties

• ex Concentrations, colour, temperature…

Steps to solve Stochiometric calculations

1. determine concentrations of known values (only gases and aqueous)

2. set up ICE table (Initial, Change, Equilibrium)

3. always in a closed system - matter can not enter or leave the system

Quantitative reaction

when a chemical reaction proceeds to completion. Happens in an open system because molecules are free to leave and there is no possibility for a reversible reaction

homogeneous equilibrium

chemical system in equilibrium where all components are the same physical states

heterogeneous equilibrium

chemical system in equilibrium in different physical states

law of chemical equilibrium (law of mass action)

The law stating that, when a system reaches equilibrium at a given temperature, the ratio of concentrations that make up the reaction remains the same.

If K>1

reaction proceeds towards completion (favours products)

If K ≈ 1

[reactants] and [products] are approximately equal at equilibrium

If K < 1

small amounts of products formed ( favours reactants)

Le chatelier's principal

If a chemical system in a state of equilibrium is disturbed, system will change equilibrium concentrations to reduce the effects of the disturbances

How does equilibrium if there is a change in concentrations?

equilibrium shifts towards the opposite side of where the concentration increased. or towards the side where the concentration decreased.

Explain the how change in concentrations effects the equilibrium

• Explained through kinetic theory

• greater concentration = more collisions = increase in products

• decrease in concentration = less collisions = decrease in products

How does volume effect the equilibrium? (Le Chatelier's principal)

• If volume increases then the pressure decreasing, to even out the pressure that decreases then the reaction will have to shift towards the side that will increase pressure (side with more moles)

• If volume decreases, then the pressure increases to even out the pressure that increases the reaction will shift toward the side that will decrease the pressure (side with less moles)

How does pressure effect the equilibrium? (Le Chatelier's principal)

• If pressure increases then reaction will have to shift towards the side decreases pressure (side with less moles)

• If pressure decreases then the reaction will shift toward the side that will decrease the pressure (side with more moles)

How does temperature effect the equilibrium? (Le Chatelier's principal)

• If temp increases reaction will shift towards the side that absorbs the heat (endothermic) side

• if temp decreases reaction will shift towards the side that releases the heat (exothermic) side

What does not have an effect on equilibrium?

1. catalysts (only effects reaction rates)

2. inert gases (changes probability of successful collisions but has no effect on equilibrium)

100's Rule

if [initial concentration] / Keq > 100, then x is considered negligible

100's Rule exception

any products that have an initial value of 0

Reaction quotient (Q)

Ratio of the concentrations of the products to the concentrations of the reactants at any point during the reaction aside from equilibrium

• used to determine where a reaction is relative to k eq

If Q>K

reaction shifts left ( too many products)

If Q ≈ K

K is at equilibrium

If Q < K

too many reactants, shift right

Solubility Equilibria (Ksp)

reactions involving the dissolving or forming of a solid from a solution

molar solubility

maximum dissolved concentration per 1 mol of substance at a given temp

common ion effect

a decrease in the solubility when an ionic compound is dissolved in a solution that already contains an ion in common with the solid

Common ion effect le Chatelier's principal

extra concentration of product shifts reaction left