1.6 & 1.10 Chemical Equilibria, Kc & Kp Flashcards
What is a closed system?
No products or reactants can escape
Nothing can enter
What is dynamic equilibrium?
When the forward and backward reaction in a reversible reaction occur at the same rate
And
The concentrations of reactants and products remain unchanged
(Happens in a closed system)
What is Le Chatelier’s principal?
When a change is applied to a system in dynamic equilibrium, the system reacts in such away to oppose the effect of the change
How will equilibrium be affected by increasing temperature?
Endothermic direction
It will try to cool the surroundings therefore take in the heat which opposes the change
How will equilibrium be affected by decreasing temperature?
Exothermic direction
It will try to heat the surroundings therefore give out the heat which opposes the change
How will equilibrium be affected by increasing pressure?
Move to the side with fewer gas particles (big number)
As fewer gas particles in a given volume causes a lower pressure which opposes the change
How will equilibrium be affected by decreasing pressure?
Move to the side with more gas particles (big number)
As more gas particles in a given volume causes a higher pressure which opposes the change
How will equilibrium be affected by increasing reactant concentration?
Equilibrium moves to the products
Right
How will equilibrium be affected by decreasing reactant concentration?
Equilibrium moves to the reactants
Left
How will equilibrium be affected by increasing product concentration?
Equilibrium moves to the reactants
Left
How will equilibrium be affected by decreasing product concentration?
Equilibrium moves to the products
Right
How will equilibrium be affected by removing C?
A+B ⇌ C+D
Concentrations after?
The equilibrium will move to the right
A+B - decreases
C - remains the same
D - increases
In industry what is significant?
You never want to equilibrium to stop so you remove your desired product to keep the required reaction going
What doesn’t affect equilibrium? Why?
Catalysts
It only increases the rate of reaction so speeds up the forward and backward reactions equally
Why is high pressure often not used? What is used?
Dangerous
Expensive
Compromise conditions
When deciding what to change in a system what should you consider?
If no state symbols are given don’t use pressure!!
What is the equilibrium constant?
Kc
It is a ratio of concentration of reactants and products at equilibrium
How do you work out Kc?
[products]
—————
[reactants]
If the moles are more than one you raise it as a power on the outside of the square brackets
What do square brackets indicate?
Concentration
What affects the equilibrium constant Kc and Kp?
Temperature
Nothing else!!
What does Kc actually tell us?
If the equilibrium is more to the left or right
Less than 1 = left
1 = Equilibrium
More than 1 = right
How do you calculate equilibrium moles?
From the two moles given of the same compound take one from the other and use the difference to work out the ‘moles’ of the rest (above compounds)
Then the ‘moles’ you worked out add or take from the starting equilibrium moles you were given in the question - depending on the reaction direction
What must you do when putting numbers into the brackets for Kc?
You work out the equilibrium moles then divide by the volume to get the concentrations
What does a high value of Kc indicate?
A high equilibrium yield of products (favours the right)
What doesn’t affect the equilibrium constant?
Change in pressure
Change in concentrations of the reactants or products
A catalyst
How do you calculate Kc units?
Each concentration = moldm^-3
Cancel them out in the fraction and move and change signs accordingly
If it has no units literally write no units
Why could actual yield differ from equilibrium yield?
If the reaction isn’t allowed to reach equilibrium
Due to the desired product being constantly removed forcing the equilibrium to keep producing it
Then equilibrium yield is never reached
What is significant about partial pressures?
The sum of the partial pressures is equal to the total pressure caused by the gas reaction
How do you work out partial pressures?
Equilibrium moles
Divided by
Total equilibrium moles
All multiplied by the total pressure
(Do this for each compound)
How to work out Kp?
(partial pressures of products)
——–——————–—————
(partial pressures of reactants)
If the moles are more than one you raise it as a power on the outside of the brackets
(Put a p just inside the bracket to indicate that it’s a partial pressure)
How do you work out Kp units?
Each partial pressure = KPa
Cancel them out in the fraction and move and change signs accordingly
If it has no units literally write no units
What would you use as the partial pressure if a compound was a solid?
1
As this is a constant
What is partial pressure?
The pressure a gas would exert individually under the same conditions
What is Kp?
The equilibrium constant for a reversible reaction that takes place completely in the GAS PHASE
