Equilibria Flashcards
(17 cards)
what is an equilibrium mixture?
Where the reactants and products of a reaction in a closed system remain constant in a reversible reaction (dynamic)
What are the conditions needed for equilibrium to occur?
-closed system so that reactants and products cannot escape (does not have to be sealed)
-can be approached from either direction and the final equilibrium position will be the same
-reached when the rates of the 2 reactions are the same
How can you tell when equilibrium has been reached?
macroscopic properties no longer change for example the density, concentration, pressure, colour as they do not depend on the total quantity of matter
In which ways is the equilibrium shifted to gain greater amounts of products and greater amounts of reactants?
greater products- right
greater reactants- left
what is le chateliers principle?
If a system at equilibrium is disturbed the equilibrium moves in a direction to counteract the change.
-does not tell us how far the equilibrium shifts so you cannot therefore predict the quantities involved.
What are the factors which effect the position of equilibrium?
-pressure
-tempreture
-concentration
-catalysts
How does pressure effect the position of equilibrium?
-an increase in pressure at a constant temp shifts the position of the equilibrium to the side with smaller gas volume/no. of moles
-a decrease in pressure at constant temp shifts position to the side with large gas volume/no. of moles
-if there is the same amount of moles of a gas on each side of the equilibrium then change in pressure will have no effect
How does tempreture effect the position of equilibrium?
-for a reaction where the forwards reaction is exothermic an increase in temp would shift position in direction of endothermic reaction to the left
-for a reaction where the forward reaction is exothermic a decrease in temp would shift position to the exothermic reaction to the right
-for a reaction where the forward reaction is endothermic an increase in temp would shift in direction of endothermic reaction to the right
-for a reaction where the forward reaction is endothermic a decrease in temp would shift in direction of exothermic reaction to the left
How does concentration effect equilibrium position?
-if more of a reactant or product is added to or removed from an equilibrium system at a constant temp and pressure it will adjust to replace any substance removed or remove any substance added
-concentration of reactant increased then position shifts to right and more products form
-by removing products position moves to right to make more products
How does a catalyst effect equilibrium position?
-no effect on position but allows reaction to reach equilibrium faster
-increase rate of forward and backward reactions equally
Describe the Haber process
-production of ammonia for fertilisers
-nitrogen reacting with hydrogen in a dynamic equilibrium
what is the effect of temperature on the Haber process?
-due to exothermic reaction forward reaction the percentage yield of ammonia is greater at lower temps but this reduces rate due to lower kinetic energies
-compromise is made and 450 degrees is used
what is the effect of pressure on the Haber process?
-increasing pressure increases the yield of ammonia as it shifts to the right
-but high pressure is expensive to maintain
-so medium pressure of 200 atmospheres are used
Comprimises made in haber process
-yield of 30%
-without being too expensive
-iron catalyst used to reach equilibrium quicker
What is homogenous equilibrium?
-where all products and reactants are in the same state
What is equilibrium constant?
-at a fixed temp means constant only if temp changes is it not constant
-subscript shows type of equilibrium
-calculated from concentrations of reactants and products
-can be calculated from reactions in a solution or homogenous gas reactions as concentration of a solution is calculated as the number of moles in a specific volume
Steps for calculating equilibrium constant
1)draw table and fill in number of initial moles, the change for each substance and equilibrium number of moles for each atom
2)convert moles to conc mol/dm3
3)state expression for kc
4)substitute values
5) work out units for kc
