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Equilibrium
graph graph
example 2example
Equilibrium
2
Equilibrium graph example 3
Summary:
- the rate of the fwd reaction is guided by the reactants and the rate of the rvs reaction is guided
by the products
- the higher the concentration the higher the rate
- reaction rates of forward and reverse reactions are equal at equilibrium
- the reactions continue to create reactant and product at equilibrium
- equilibrium is the spot on the graph where concentration lines run parallel
- concentrations of reactant and product are not necessarily equal at equilibrium (more to
come on this....)
At the beginning of a chemical reaction, there is nothing but reactant
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the speed of a reaction is determined by the concentration of:
- reactants for the forward reaction
- products for the reverse reaction
So at the beginning of a reaction the rate of the forward reaction is fast and the reverse reaction
is non-existent/very slow. As the reaction progresses and reactants turn into products, the
concentration of products starts to increase. This makes the rate of the reverse reaction increase
Eventually the concentrations of reactant and product are equal meaning the rate of the
forward and reverse reactions are equal as well. This is when equilibrium is established (reaction
keeps going)
Misconceptions about equilibrium:
1. at equilibrium, concentrations of reactants and products are equal
2. the reaction must be finished because the concentrations aren't changing
What equilibrium equations tells us:
- each cat fights with one dog and each dog fights with one cat
- a fight consists of 1 dog and 1 cat
- fighting couples form and break up
What equilibrium equations do not tell us:
- how many cats in total vs. how many dogs in total
- how many current single dogs and cats vs. how many fights
Equilibrium graph example 1
Unit 2: Chemical Equilibrium
Big Idea: Consider qualitatively and quantitatively the characteristics and applications of
equilibrium systems in chemical reactions
What do you know about valence equilibrium?
https://www.youtube.com/watch?v=dUMmoPdwBy4
Indicator: Discuss why most chemical reactions do not proceed to completion
Some chemical reactions proceed to completion:
CH4 + O2 ---> CO2 + H2O
Combustion
reaction goes until all of the reactant is converted to product
Most reactions do not go to completion:

instead they approach an equilibrium state in which both reactants and products are present

This occurs because the reaction is reversible

the products formed by the reaction can themselves react to form the original reactants
Reversible reactions can reach equilibrium
Equilibrium: for a reversible reaction, a dynamic state in which the rate of the forward reaction
is exactly equal to the rate of the reverse reaction
Equilibrium equation
2 way arrow = reversible reaction
Indicator: Discuss criteria for equilibrium
Requirements for equilibrium:
1. can only occur in a closed system
2. rates of the forward reactions is the same as the rate of the reverse reaction
3. constancy or properties for the chemicals involved (ex: colour stays the same)
When a reactions reaches equilibrium:
1. the rates of the forward and reverse reactions are equal
2. the concentrations of the reactants and products are constant (not necessarily equal)
How does a reaction get there?