3.2.3 Chemical Equilibrium Flashcards
what do reversible reactions take place in
- “forward” and “backward” reactions
- using the ⇌ symbol
why is a dynamic equilibrium - 3 POINTS
- where the rate of the forward reaction is equal to the backward reaction
- and the concentrations of the reactants and products do not change
- in a closed system
why is it a DYNAMIC equilibrium
- both the forward and backward reactions are still taking place
- it’s just that their rates are equal
- so concentrations do not change
why does a dynamic equilibrium need a closed system
- is isolated from surroundings
- so that the temperature, concentration and pressure of the reactants is unaffected by outside influence
what is Le Chatelier’s Principle
when a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effects of that change
explain the position of equilibrium
- indicates the extent of a reaction, and is changed by external factors
how does concentration affect the position of equilibrium
- if you increase the concentration of reactants
- the position of equilibrium shifts to the right
- to favour the forward reaction, forming more products
how can you investigate the effect of concentration of position of equilibrium
by using reactants and products of different colours
how can you use dichromate ions to investigate position of equilibrium
2CrO4 2- + 2H+ ⇌ Cr2O7 2- + H2O
- CrO4 = yellow
- CrO7 = orange
1) add yellow K2CrO4 to beaker
2) if you add H2SO4, it turns ORANGE, as you increase conc. of H+ ions, so conc. of reactants increases, increasing rate of forward reaction, equilibrium shifts and Cr2O7 forms
3) if you add NaOH, you add OH- ions, which react with H+ ions, decreasing their concentration, decreasing conc, of reactants, so forward reaction decreases, equilibrium shifts to minimise change - YELLOW
how does temperature affect equilibrium
- the ΔH of forward and backward reactions are the same, but have opposite signs
- one is endo and one is exo
- increase in temperature shifts equilibrium to the endothermic direction
- decrease in temperature shifts the equilibrium to the exothermic direction
how can you perform an experiment to investigate the effect of temperature on the position of equilibrium
- use a known equilibrium
- first place is boiling water:
- you increase the heat energy of the system, equilibrium shifts to the endothermic direction, taking heat energy in and minimising the increase in temperature
- when placed in ice cold water:
- shifts to the exothermic side, to give out energy to counteract the decrease in temperature
how does pressure affect the position of equilibrium
ONLY VALID FOR GASES
- first figure out the amount of moles of gases present on each side to see the relative pressure
- increasing pressure will shift the equilibrium to the side with fewer molecules, reducing the pressure of the system
how do catalysts affect the position of equilibrium
- catalysts only speed up rate of reaction
- NO effect on the position of equilibrium
- as both the forward and backward reactions are sped up equally
- so increases the rate at which the equilibrium is established, not its position
what is the equation of the Haber process
N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = -92
what is the temperature used in the Haber process
- need a low temp to shift to the right
- BUT would slow down the rate of reaction too much
- so 350-500°C is used as a compromise
