Topic 10: Equilibria I Flashcards
What would be characterised as an irreversible reaction?
When hay very little, if any reactant left in the reaction then it is irreversible.
Most combustion reactions are irreversible bc the enthalpy change is negative and v large.
What occurs if reactions have a small enthalpy change?
If reactions have a small enthalpy change the reactions may not go to completion.
This may mean trace amounts of reactant mixed w product may remain.
These are reversible reactions
How would you describe a reaction that has gone to completion?
In practical terms if it is 99% complete, then it has gone to completion
Describe the reaction entre H2 and I2
If H2 and iodine vapour are heated together at 573k in a 1:1 ratio in a closed container, 10% will remain unreacted no matter how long the reaction is left for.
If hydrogen iodide is heated to 573k in a closed container it partially decomposes to form OG reactants.
The reaction is therefore reversible and the system is in eqm:
H2+I2(g)—>2HI(g)
How is eqm established?
Eqm is established when the forward and backwards reactions of a reversible reaction are going at the same rate.
There is no further change in concs of reactants and products
What is dynamic eqm? State the conditions for it
Dynamic eqm is when the forwards and backwards reactions in a reversible reaction take place at the same rate and time.
Conditions:
Reactions must be reversible in a closed system
Rate of forward= rate of backward reaction.
Both forward and back reactions must continuously occur.
Concs of reactants and products must remain constant
What happens when equilibrium lies to the left vs towards the right?
When eqm lies to the right: lots of product not much reactant
When eqm lies to the left: lots of reactant, not much product.
What happens if there is a change to the closed system?
The eqm position will shift to oppose the change. Changes include concentration, pressure, temperature, (catalyst).
What happens if you increase reactant concentration to a reaction in equilibrium?
The rate of the forward reaction increases and more product will form.
As product concentration increases, the rate of backward reaction increases and eventually a new eqm position is established.
Overall the eqm position moves to the right, y hay mas product.
Decreasing reactant concentration shifts equilibrium to the left.
What happens if you increased product concentration in an equilibria reaction?
The rate of the backwards reaction increases and more reactant forms. As reactant conc increases, the rate of the forward reaction increases and eventually a new eqm position is established. Overall the eqm position moves to the left, y hay mas reactant.
Decreasing product concentration shifts to the right
How do you increase or decrease the pressure of reaction?
Pressure is increased by reducing the volume, or using more moles of reactants in the same volume.
Pressure is decreased by increasing the volume or using less moles of reactants in the same volume.
Describe the effect of pressure on a reaction in equilibria
Increasing pressure shifts to the side with the fewest gas moles. Decreasing pressure shifts to the side with more moles of gas.
If the number of moles are the same on both sides, there is no change. Pressure only applies to reactions with gases at a given temperature.
Describe the effect of temperature on a reaction in equilibria
Increasing temperature increases the rates of both forwards and backwards reactions, but there will be greater increase and the eqm will shift to the endo side. Decreasing temperature shifts to the exo side
Describe the effect of a catalyst on a reaction in equilibria
A catalyst increases the rates of both forwards and backwards reactions.
The eqm position is unaltered but it is reached faster.
What is the limitation of making qualitative predictions?
Qualitative predictions are just predictions, not explanations of why changes sometimes occur.
Some occasions are impossible to predict the direction of change.
