Chemical Equilibrium
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54 Terms
What is chemical equilibrium
The rate of the forward reaction equals the rate of the reverse reaction
What is dynamic equilibrium
Forward and reverse reactions occur at the same time and are ongoing
What symbol shows a reversible reaction
⇌
What happens to reactant and product amounts at equilibrium
They remain constant at that temperature
Has a reaction stopped at dynamic equilibrium
No, both reactions are still occurring
State Le Chateliers principle
When a system at equilibrium is subjected to a stress such as a change in temperature, pressure or concentration the system will alter to oppose the effect of the stress.
What happens if a substance is added at equilibrium
The system shifts to use it up
What happens if a substance is removed at equilibrium
The system shifts to make more of it
What happens when temperature is increased
The endothermic reaction is favoured
What happens when temperature is decreased
The exothermic reaction is favoured
What does negative ΔH mean
The forward reaction is exothermic
What does positive ΔH mean
The forward reaction is endothermic
What happens if ΔH is zero
A temperature change does not change equilibrium position
When does pressure affect equilibrium
Only for gaseous systems
What happens when pressure is increased in a gas equilibrium
The side with fewer gas moles is favoured
What happens when pressure is decreased in a gas equilibrium
The side with more gas moles is favoured
What if gas moles are equal on both sides
Pressure has no effect
Does pressure affect non gaseous equilibrium
No
What is Kc
The equilibrium constant in terms of molar concentrations
Where do products go in a Kc expression
On top
Where do reactants go in a Kc expression
On bottom
What do powers in Kc come from
The balanced equation coefficients
What does Kc greater than 1 mean
More products than reactants at equilibrium
What does Kc less than 1 mean
More reactants than products at equilibrium
What is the only factor that changes Kc
Temperature
Does a catalyst change Kc
No
Does a catalyst change equilibrium yield
No
What does a catalyst do in equilibrium
It helps equilibrium to be reached faster
What is used to make hydrogen for the Haber process
Steam reforming of natural gas
What is the steam reforming equation
CH4 + H2O ⇌ CO + 3H2
What is the Haber process equation
N2+3H2⇌2NH3
What catalyst is used in the Haber process
Finely divided iron
What promoter is used in the Haber process
Aluminium oxide
What temperature is used in the Haber process
About 500 °C
What pressure is used in the Haber process
About 200 atm
Why is low temperature ideal for Haber yield
The forward reaction is exothermic
Why is very low temperature not used in Haber
The reaction would be too slow
Why is high pressure ideal for Haber yield
The product side has fewer gas moles
Why is very high pressure not used in Haber
The plant is costly to build and maintain
Name two uses of ammonia
Fertilisers and nitric acid
What is the Fe3 plus thiocyanate equilibrium
Fe3+ + CNS- ⇌ Fe(CNS)2+
What colour is Fe3+ in the thiocyanate experiment
Yellow
What colour is Fe(CNS)2+
Red
What happens when HCl is added in the thiocyanate experiment
The solution becomes yellow
What happens when FeCl3 is added in the thiocyanate experiment
The solution becomes red
What happens when the red thiocyanate solution is heated
The red colour intensity decreases
What does heating the thiocyanate system show
The reverse reaction is endothermic
What is the bismuth precipitate in the notes
BiOCl
What colour is the bismuth precipitate
White
What happens when water is added to the bismuth equilibrium
A white precipitate appears
What happens when concentrated HCl is added to the bismuth equilibrium
The white precipitate dissolves
What happens to Kc if an equation is reversed
New Kc is 1 over old Kc
What happens to Kc if an equation is doubled
New Kc is old Kc squared
What happens to Kc if an equation is halved
New Kc is square root of old Kc