Chemical equilibrium Flashcards
Open system
A system which continuously interacts with its environment
A system in which mass or energy can be transferred into or out of the system during a reaction (heat)
equil. can never be reached if gases involved
Closed system
A system which is isolated from its surroundings
A system in which mass or energy cannot be transferred into or out of the system. (no heat)
The container must be sealed.
Reversible reaction
A reaction where products can be converted back into reactants.
A reaction which does not go to completion and occurs in both directions.
Dynamic equilibrium
State where no visible change (macroscopically) but microscopically reaction in both directions occuring… chemical equilibrium.
Refers to the fact that the forward and reverse reactions continue to take place simultaneously,sometimes at the same rate.
Chemical equilibrium
It is a dynamic equilibrium
When the rate of the forward reaction equals the rate of the reverse reaction
Le Chatelier’s principle
NB: When the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will oppose the disturbance.
A change in any of the factors that determine equilibrium conditions of a system will cause the system to change in such a way as to reduce or counteract the effect of the change
Factors that affect the chemical equilibrium position
- Concentration
- Temperature
- Pressure
List 5 good things to do when structuring an explanation based on equilibrium positions
- Le Chatelier’s principle … counteract
- Use up(added)
or Replace(removed) - Forward or reverse reaction favoured
- Concentrations increase and decrease
- Equilibrium shifts to the left or right
Reminder ΔH
Exothermic ΔH<0 , a reaction which releases more energy than is absorbed
Endothermic ΔH>0 , a reaction which absorbs more energy than is released
Effect of temperature changes on the equilibrium position
Increase in temperature - favours the endothermic reaction
Decrease in temperature - favours the exothermic reaction
pressure and equilibrium position realtionships
Does not affect solids and liquids. only gases and aqueous solutions. The concentration of solids cannot change.
Look at #moles of gas on each side of the equation
Effect of pressure changes on the equilibrium position
Increasing pressure favours the reaction that proceeds towards the fewer #moles (of gas)
Decreasing pressure favours the reaction that proceeds towards the greater #moles (of gas)
Effect of catalysts changes on the equilibrium position
Catalysts do not affect the equilibrium position. Because they increase the rate of the forward and reverse reactions equally.
What occurs if a catalyst is added to a system that is not yet in equilibrium
Equilibrium would be reached sooner with a catalyst compared to a system without one
But the equilibrium position itself would not change because of the presence of the catalyst.
Discuss the common ion effect
If a compound is added to a system in equilibrium and that compound contains an ion already present in the equilibrium system
Then the reaction that uses up that ion will be favoured.
State the reaction for the Haber process and give a short ‘definition’
An industrial process for the formation of ammonia NH3
N2 (g) + 3 H2 (g) 2NH3 (g) ΔH<0
Yield
Affects in industrial processes
The amount of product obtained in a chemical reaction
In industrial process need to balance between financial cost, yield and time
What does a large Kc value indicate (generally)
It means that there are more products than reactants present in the container at equilibrium
What does a small Kc value indicate (generally)
It means that there are more reactants than products present in the container at equilibrium
What is Kc
The equilibrium constant (of a specific reaction)
What only factor that can change the Kc value
Temperature
Explain the following formula
c = n/v
Concentration ( in mol.dm-3) = number of moles (mol) / Volume of container (litres or dm3)
Explain the following formula
n = m/M
Number of moles (mol) = mass(g) x Molar mass (g.mol-1)
If the Kc is greater/less than 1 then…
greater than 1, products > reactants
smaller than 1, reactants > products
In an equilibrium graph, when all the liens are straight and parallel to one another then..
The system is in equilibrium as the concentration of the reactants and the products are constant
