Chemical equilibrium Flashcards
Describe a reversible reaction
A reversible reaction is one that can occur in either direction.
3 Characteristics of a dynamic equilibrium
- The rate of the forward reaction reaction is the same as the rate of the backwards reaction.
- Concentration of the reactants and products do not change- remians constant.
- The system must be closed.
Defintion of Le Chatelier’s principle
When any of the conditions affecting the position of a dynamic equilibrium are changed, then the position of the equilibrium will shift to minimise that change.
Things to ALWAYS state
Which reaction is favoured- forwards or backwards?
Why- Concentration, temperature (endothermic, exothermic), pressure (number of gaseous moles)?
Which way did the equilibrium shift- state left or right?
What is a homogenous equilibria?
Reactants and products are in the same state.
Increasing temperature always favours the…
endothermic reaction.
Decreasing the temperature always favours the…
exothermic reaction.
Explain the effect that addition of a catalyst has on a reaction.
The rate will increase. This is because it provides an alternative route with a lower activation energy. Therefore, a catalyst has no effect on the position of the equilibrium as the rates of the forwards and backwards reactions will increase equally.
Which reaction does the enthalpy change represent when given in the qu?
It is ALWAYS the FORWARD REACTION.
To achieve a high yield in the Haber process, the optimum conditions are…
- Low temperatures.
- High pressure.
What are the problems with the conditions required for the Haber process?
A low temperature causes a low rate.
A high pressure has high energy costs and safety considerations.
Explain the compromise of the conditions for the Haber process
The compromise is to use a reasonably high temperature to give a good reaction rate but not high enough to reduce the yield too much as equilibrium moves slightly to the left and pressure used is above atmospheric pressure. The pressure is quite high to push gases together to help the reaction proceed and increase the rate (more frequent and successful collisions), also shifts the equilibrium to the right and increases yield. Pressure is not so high as to be too energy intensive or raise safety concerns.
Explain the effect of a catalyst on the Haber process
Iron is used. It is a heterogenous catalyst. This increases the rate. Increasing the rate this wayallows for a lower temperature to be used so lower energy costs.
What is Kc?
An equilibrium constant (c means concentration). It is a value that is calculated for any homogenous reaction.
What is a homogenous reaction?
A reaction in which the reactants and products are in the same state.
