Topic Eight: Chemical equilibria

Define reversible reactions

They are reactions where the reactants form products that can react with each other to reform the reactants, allowing reaction to proceed in either direction

Define dynamic equilibrium

It is a reversible reaction ar equilibrium in which the rate of the forward reaction equals to the rate of the backward reaction, and the concentrations of reactants and products do not change

State the 4 characteristics of a reaction in a state of dynamic equilibrium

Concentration of all reactants and products remain constant, rate of forwards reaction equals to rate of backward reaction, there is a closed system where there is no net gain or loss of substances from the surroundings and the equilibrium can be achieved from either directions

State what Kc and Kp measures and how they differ from each other

Kc and Kp both measures the proportion of products to reactants in an equilibrium mixture, except Kp is for gaseous reactants and they use partial pressure instead of concentration.

Define homogenous and heterogenous equilibrium

Homogenous equilibrium involves substances that are all in the same phase while hetergenous equilibriums involves substances of different phases

State why sometimes, H2O is omitted from Kc expressions and when it will be included

They are omitted when H2O is the solvent for the reaction, hence it is in large excess and will stay relatively constant even with H2O being formed as a product. Whereas, if H2O is only formed in products and all species are miscible(all in liquid states), then it will be included

What reactants other than water, are also omitted from Kc expressions

Solids, as their concentrations are relatively constant

State the conversion for kPa to Pa and from Pa to atm

1kPa is equals to 1000Pa and 1Pa is equals to 101325 atm

Determine how Kc and Kp expressions show the POE of a reaction in equilibrium

If Kc and Kp is much larger than 1, then POE lies far right. If Kc and Kp is much smaller than 1, then POE lies far left

What does Kc and Kp not provide information on

They do not indicate the rate of forward and backwards reaction and they do not indicate the time required to reach equilibrium

How can gibbs free energy value be used to determine the direction of reaction and spontaneity

If the value is less than 0, then the reaction proceeds in forward direction and is spontaneous. If the value is more than 0, then the reaction proceeds in backward direction and is spontaneous. If the value is equals to 0, then the system is in dynamic equilibrium and rate of forward reactions is equal to rate of backward reaction

State the equation relating gibbs free energy and equilibrium constant

G=-RTlnK

What does Le Chatelier’s principle state

It states that if a system in equilibrium is subjected to a change which disturbs the equilibrium, the system will respond in a way to counteract the effect of the change imposed, in order to re-establish the equilibrium of the system

How does the addition of noble gases at constant pressure affect POE (pV=nRT)

When noble gases are added, n increases, and since p must be constant, V will increase. This results in POE shifting to the direction with more number of gaseous particles

Describe what happens to POE when noble gases are added at constant volume (pV=nRT)

When noble gases are added, n increases, and since V has to stay constant, p will increase. POE will remain unchanged when pressure increases

Explain why temperature affects the Kc and Kp value too

When POE shifts to favour the endothermic or exothermic reactions, the products formed at equilibrium will either decrease or increase, hence increases or decreasing Kc and Kp value

Describe the effect of adding a catalyst on POE

Since catalyst only increases rate of reaction by providing an alternative reaction pathway with lower activation energy without being chemically changed itself, POE is unchanged as rate of forward and backward reaction are increased by the same extent and the equilibrium will simply reach faster

State the conditions for haber process and explain why they are used

A temperature of 450 is used as lower temperatures allow POE to shift right to favour the exothermic reactions to form more products, but a lower temperature also reduces the frequency of effective collisions and reduce the chances of breaking the strong N-N triple bond, hence a compromise of 450 is used. A pressure of 250atm is used as higher pressures would cause POE to shift right and form more ammonia and it also brings molecules closer together to increase frequency of effective collisions, but higher pressures have a higher capital cost, hence a compromise of 250 is used. A finely divided iron catalyst is used to increase rate of reaction

State an additional process that increases yield of ammonia in Haber process

Ammonia gas formed will be cooled while still maintaining constant pressure, allowing it to form a liquid and can be removed constantly, hence POE will continuously shift right to produce more ammonia