Dynamic Equillibrium Flashcards
When all reactants are used up, it is said that the reaction has gone to _____. Many reactions do not go to completion and both reactants and products are present.
completion
When is a state of dynamic equilibrium reached?
In such cases, a state of dynamic equilibrium is reached when the original substances are reacting at the same rate as the new substances are reacting with each other to form the original substances.
What the two conditions for dynamic equilibrium?
- The system must be closed and a reversible reaction must exist.
- The rate of the forward reaction equals the rate of the reverse reaction.
What do we mean when we say equilibrium is dynamic?
Equilibrium is dynamic. The reaction has not stopped, both forward and reverse reactions are occurring at the same rate.
What type of system is equilibrium achieved?
Equilibrium is achieved in a closed system. A closed system is necessary so that neither reactants or products can escape. Both need to be present to react.
The concentrations of reactants and products remain constant at _____, Reactants and products are both being used and produced at ____ rates.
equilibrium
equal
At equilibrium it looks as though the reaction has stopped. ______ observable changes do not occur.
Macroscopically
Which direction can equilibrium be achieved?
Equilibrium can be reached from either direction. The same equilibrium mixture will form under the same conditions irrespective if you started with only reactants, only products or a mixture of both.
Will there be any change after equilibrium is reached?
Once equilibrium is established in a system, no further change is apparent as long as the external conditions remain unchanged. If the external conditions are changed then the system will shift to a new state of equilibrium. Whether the equilibrium will shift towards more products or more reactants can be predicted using Le Chatelier’s Principle.
What are the useful steps to go through when using Le Chatelier’s Principle?
When using Le Chatelier’s Principle, it will be useful to go through the following
steps:
• Identify the disturbance
• State that the system will oppose this disturbance
• Decide whether the forward reaction or reverse reaction is favoured.
• Discuss the result, what is observed.
How does concentration affect equilibrium? With reference to this equation: A + B ⇌ C + D
If the concentration (not just amount) of either A or B or both is increased, the forward reaction is favoured so as to relieve the stress. If the concentration of C or D or both is increased, the reverse reaction will be favoured so as to relieve the stress. Note: The concentration of pure solids and liquids cannot be changed.
(i.e. by adding more solid the concentration does not increase.)
How do pressure changes affect equilibrium?
If pressure is increased the reaction which counteracts the effects of the stress (i.e.increased pressure) is favoured. i.e. Increased pressure favours the reaction
producing the smallest number of moles. For decreased pressure the reverse is true.
How does temperature affect equilibrium?
If the temperature of a reaction mixture is changed, the equilibrium will shift to minimize that change.
• If the temperature is increased the equilibrium will shift to favour the reaction which will reduce the temperature. The endothermic reaction is favoured.
• If the temperature is decreased the equilibrium will shift to favour the reaction which will increase the temperature. The exothermic reaction is favoured.
Note: An increase in temperature will increase the rates of both forward and reverse
reactions, but will initially favour one of the reactions more.
The forward reaction is ____ which means the reverse reaction is endothermic. Increasing the temperature of the reaction will favour the _____ reaction.
exothermic
endothermic
How does a catalyst affect equilibrium?
A catalyst does not alter the position of the equilibrium. Catalysts only cause equilibrium to be reached sooner by increasing the rate of both the forward and the reverse reaction equally. (Le Chatelier’s Principle is not applicable for catalyst addition)
