3.2.3 Chemical Equilibirum Flashcards
What is dynamic equilibrium
Rate of forward reaction is equal to rate of reverse reaction
Concentration of reactants and products do not change
Closed system
Effect of concentration on equilibrium
If concentration increases to the right to form more products, position of equilibrium shifts to the left
If concentration increases to the left to form more reactants, position of equilibrium shifts to the right
How to investigate effect of concentration on position of equilibrium
Aqueous chromate ions are yellow and dichromate ions are orange
Position of equilibrium is sensitive to acid conc.
Adding dilute H2SO4 to yellow potassium dichromate turns it orange
Adding aqueous sodium hydroxide turns it back yellow
Adding dilute H2SO4 increases concentration of H+ which increases rate of forward reaction and causes position to shift to minimise change in concentration
Equilibrium shifts to the right and more dichromate forms, turns orange
NaOH does the opposite, equilibrium shifts to left, solution turns yellow as chromate ions form
Effect of temperature on position of equilibrium
Increase in temperature shifts equilibrium in the endothermic direction (+∆H)
Decrease in temperature shifts equilibrium in the exothermic direction (-∆H)
How to investigate effect of temperature on position of equilibrium
Dissolve cobalt chloride in water in a boiling tube, add small amount of hydrochloric acid
Place solution in iced water, creates pink solution
Set up boiling water bath and transfer boiling tube, solution turns blue
Forward reaction is endothermic, position of equilibrium shifts to right in endothermic direction in the boiling water to take energy in and minimise increase in temp, so solution turns blue
In iced water, equilibrium shifted to the left to exothermic direction
Effect of pressure on position of equilibrium
Increasing pressure shifts equilibrium to the side with fewer moles to minimise the increase in pressure
Decreasing pressure shifts equilibrium to the side with more moles
Effect of catalysts on the position of equilibrium
No change to position of equilibrium, speeds up rate of forward and backward reactions equally
Reasons for compromise in industry between equilibrium and reaction rate when deciding on conditions
In ammonia production, low temp would produce high yield but would occur slowly, meaning equilibrium might not be established
High pressure increases yield and increases conc and rate of reaction but it requires a strong container and lots of energy which increases cost and is a safety hazard
Equation for equilibrium constant
For reaction aA + bB -> cC + dD
Kc = [C]^c[D]^d ÷ [A]ª [B]^b
Kc = [products] ÷ [reactants]
What do Kc values tell us
Kc value of 1 indicates position of equilibrium is halfway between reactants and products
Kc value > 1 indicates position of equilibrium is towards products
Kc value < 1 indicates position of equilibrium is towards reactants
