Chemical Equilibrium

reversible reaction

reaction in which the products react to give back the reactants, the reaction is going in both directions

When can we say a reversible reaction is finished

when we have produced the maximum amount of all substances in the system as possible at that particular temperature

CHEMICAL EQUILIBRIUM

when there is a state of dynamic balance in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction.

DYNAMIC EQUILIBRIUM

equilibrium that exists in a closed system when both the forward and backward reactions occur at the same time. They are ongoing and the concentrations of the reactants and products remain the same.

LE CHATELIER’S 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.

if a substance is removed in a reversible reaction, what happens

the reaction that MAKES that substance will be favoured

if a substance is ADDED in a reversible reaction, what will happen

the reaction that USES UP THAT SUBSTANCE will be favoured

If the temperature is decreased, what happens and why

the EXOTHERMIC reaction will be favoured, this is because exothermic reactions LOSE HEAT and this heat will replace the heat that was removed

if the temperature is INCREASED, what happens and why

the ENDOTHERMIC REACTION will be favoured. This is because endothermic reactions take in heat and this will remove the extra heat that was given to the system.

How do we know if a reaction is endo or exothermic

number after triangle + H

• forward reaction is EXOTHERMIC when the number is NEGATIVE, the reverse reaction will therefore be endothermic

when will pressure effect chemical equilibrium

• in gaseous systems

• with unequal moles

what happens when pressure is INCREASED in a gaseous system

the system will favour the side with LESS MOLECULES as this will decrease the volume and bring the pressure back down

what happens when pressure is DECREASED in a gaseous system

the system will favour the side with MORE MOLECULES as it will increase the volume and bring the pressure back up

What happens when there are equal numbers of moles on both sides of the equation in a gaseous system?

no effect on the position of equilibrium

effect of catalysts on the position of equilibrium

A catalyst will alter both the forward and reverse reactions to the same extent and therefore it will not change the position of equilibrium. Equilibrium will be reached either faster or slower with a catalyst

Kc

THE EQUILIBRIUM CONSTANT in terms of molar (mol/l) concentrations

What is the ONLY factor that will cause a change in the value of KC

temperature

what does a top heavy fraction in chem equilibrium signify

kc will be greater than one, equilibrium lies on the RHS and there is more RHS than LHS present at equilibrium

what does a bottom heavy fraction signify in chem equilibrium

Kc is less than one, more LHS than RHS present at equilibrium, and equilibrium lies on the LHS

Q: Why is chemical equilibrium known as a dynamic state?

A dynamic state means the forward reaction and reverse reaction CONTINUE to occur

at the same time and DO NOT STOP

Q: Does a reaction at equilibrium cease? Explain.

No, the system is in a dynamic state – rate of forward reaction equals rate of reverse reaction

The Haber process chem equation

N_2(g) + 3H_3(g) <=> 2NH_3(g)

Steam reforming of natural gas (use?)

manufactures hydrogen gas

Steam reforming of natural gas temperature

+205kjmol

Steam reforming of natural gas equation

CH_4(g) + H₂O_(g) <=> CO _(G) + 3H_2(g)

What is the benefit of using a catalyst in the Haber process if catalysts do not have an

effect on the state of equilibrium?

ammonia can start to be produced more quickly

In order to maximise the yield of ammonia, what temperature conditions should be used in the Haber process?

low temperature as the forward reaction is exothermic and is favoured - more ammonia is yielded

whats wrong with the low temperature favoured of the haber bosche process, whats the compromise

at low temperatures, rate of reaction is low and ammonia is produced to slowly to be economically worth it, compromise temperature is 500

In order to maximise the yield of ammonia, what pressure conditions should be used in

the Haber process? whats the drawbacks and compromise

high pressure, but can be dangerous and expensive, so 200 is compromise

Importance of ammonia industrially

Ammonia is used to manufacture:

➢ Fertilisers

➢ Explosives

➢ Cleaning products