equilibria Flashcards
(15 cards)
What is a reversible reaction?
-a chemical process where reactants can form products, and the products can react to reform the original reactants
- All reversible reactions reach a dynamic equilibrium state
What does it mean when a system has reached dynamic equilibrium?
- The forward and backwards reactions are occurring at the same rate
- The concentration of reactants and products stays constant.
What is Le Chatelier’s principle?
- If an external condition is changed, the equilibrium will shift to oppose that change.
- e.g. if the temperature is increases, the equilibrium will move in the endothermic direction to try to reduce the temperature by absorbing heat.
What is the effect of pressure on equilibrium?
- Increasing pressure will cause the equilibrium to shift
towards the side with fewer moles of gas to oppose the
change and thereby reduce the pressure. - If the number of moles of gas is the same, then changing the pressure will have no effect on the equilibrium.
What is the effect of concentration on equilibrium?
Increasing the concentration will cause the equilibrium to shift towards the side with the lowest concentration to oppose that change and thereby reduce the concentration.
What is the effect of catalysts on equilibrium?
- No effect of the position of equilibrium, but it will speed up the rate at which the equilibrium is reached.
What is the problem with increasing the temperature and pressure to get a better yield?
High pressure leads to too high energy costs for pumps to produce the pressure and too high
equipment costs to have equipment that can withstand high pressures. And the energy required for high temps is costly.
What is equilibrium law?
- at equilibrium for the reaction: aA + bB -> cC + dD
- The equilibrium constant Kc is defined as:
- Kc + [C] c[D]d/ [A]a [B]b
What happens to the equilibrium constant if you change the concentration of the system?
- The equilibrium constant will not change if you change the concentrations at equilibrium.
- Only temperature affects the equilibrium constant.
What are the units of kc?
- The units of kc can change depending on the exact equilibrium expression; it can also be unitless.
- You have to cancel out the units of the reaction to get the final unit.
What does KC mean?
- KC shows how far a reaction will proceed
- The rate expression shows how fast this will be attained.
What does the calculation of kc involve?
- Calculation of equilibrium moles present using an ICE table.
- Calculation of equilibrium concentrations
- Determination of Kc
What is an ICE table?
a table that shows the Initial number of moles, the Change in moles, and the Equilibrium number in moles
How do you use an ICE table?
- Figure out the initial number of moles in reactants and products
- Figure out the change in moles
- The equilibrium number of moles will be the initial number minus the change in moles.
How do you calculate the concentration of the equilibrium
concentration = moles/ volume.
