equilibria Flashcards
What is a reversible reaction? What can you say about energy transferred in
reversible reactions?
In reversible reactions, reactants can turn into the products and products can turn
into the reactants. Reversible reactions will be exothermic in one direction and
endothermic in the other. They will transfer the same amount of energy in each
direction.
How can you make a reversible reaction reach equilibria
. A reversible reaction must be placed in a closed system
Define ‘dynamic equilibrium’
The forwards and backwards reactions are happening at the same rate. The
concentration/amount of reactants and products stays the same.
What is ‘Le Chatelier’s Principle’
When a change is made to a system at equilibrium, the equilibrium will shift to oppose
the change
How does concentration affect equilibrium position?
If the concentration of one substances is suddenly decreased, then the equilibrium
will shift to increase the concentration of that substance.
If the concentration of one substance is suddenly increased, then the equilibrium will
shift to decrease the concentration of that substance
How does temperature affect equilibrium position?
An increase in temperature will favour the endothermic reaction because this takes in
heat so reduces the temperature.
A decrease in temperature will favour the exothermic reaction because this releases
heat so will increase the temperature
How does pressure affect equilibrium position?
An increase in pressure will favour the reaction that makes less moles of gas because
this will decrease the pressure.
A decrease in pressure will favour the reaction that makes more moles of gas because
this will increase the pressure.
If there are the same number of molecules of gas either side of the arrows, a change
in pressure will have no effect.
How does adding a catalyst affect equilibrium position?
Adding a catalyst has no effect on the equilibrium position as it speeds up the
forwards and backwards reactions equally.
State and explain the factors that increase the rate of reaction?
Increasing the concentration of a solution - this increases the frequency of
(successful) collisions.
Increasing the pressure of a gas - this increases the frequency of (successful)
collisions.
Increasing the temperature - this increases the frequency of successful collisions.
Adding a catalyst – this lowers the activation energy of the reaction so more particles
have enough energy to react.
When are compromise conditions used for industrial equilibrium reactions?
If conditions for the highest equilibrium yield and rate of reaction don’t agree a
compromise condition is used. This is usually a medium/moderate condition.
What does a Kc value that is greater than 1 mean?
Kc value that is greater than 1 means the equilibrium is far to right hand side (more
products instead of reactants)
What method can you use to work out equilibrium number of moles if given information
about starting number of moles?
ICE table
If you are given Kc for a forwards reactions, how can you calculate Kc for the
backwards reaction?
Kc for backwards reaction is reciprocal for forwards reaction. i.e 1/Kc
Which conditions (concentration/temperature/pressure/catalyst) affect the value of
Kc? Explain how they affect Kc for an exothermic forwards reaction and then an
endothermic forwards reaction
Only temperature affects the value of Kc. For an exothermic reaction, decreasing the
temperature increases Kc and increasing the temperature decreases Kc. For an
endothermic reaction, increasing the temperature increases Kc and decreasing the
temperature decreases Kc
