Chemical Equilibria Flashcards
dynamic equilibrium meaning
Reversible process at equilibrium in which rate of forward reaction is equal to rate of backward reaction
When does equilibrium constant change?
Only when temperature changes
What does a large Kc/Kp value imply?
High proportion of products compared to reactants (high product-reactant ratio), equilibrium position lies to the right, products favoured
What is the total pressure exerted by a mixture of gases which do not react?
Sum of partial pressures of the constituent gases
State Le Chatelier’s principle
If a system at equilibrium is subjected to a change which disturbs the equilibrium, the system responds in such a way to counteract the effect of the change.
Effect of change in concentration/partial pressure on equilibrium and equilibrium constant
As concentration of a reacting substance increases, equilibrium position will shift to a direction that will consume some of it/ if substance is removed, eqm position will shift in direction to replenish some of it.
No effect on Kc/Kp
Effect of change in pressure on equilibrium/equilibrium constant
When total pressure of gaseous mixture increases (by decreasing the volume), eqm position will shift in the direction that tends to reduce the pressure by decreasing total number of gaseous molecules in the system.
No effect on the Kc/Kp
Note if there are same number of gas molecules on both sides of equation, shifting of eqm position to either side will not change the pressure of the system, hence eqm not affected.
Effect of change in temperature on equilibrium/equilibrium constant
If temperature increase, eqm position will shift in direction that favours endothermic reaction to absorb some of the added heat.
If temperature decrease, eqm position will shift in direction that favours exothermic reaction to release some heat.
When less products formed: Kc/Kp decreases
When more products formed: Kc/Kp increased
If enthalpy change is 0, no effect on Kc/Kp
Effect of catalyst on equilibrium/equilibrium constant
Catalyst increase rates of both forward and backward reactions by same extent, hence increases rate at which equilibrium is established.
No effect on equilibrium position and Kc/Kp
Conditions of haber process
Temperature: 450*C
Pressure: 250atm
Catalyst: finely divided iron (mixed with small amounts of potassium oxide and aluminium oxide as promoters
Explain temperature condition of haber process
Forward reaction is exothermic, decreasing temperature will shift position to the right, increasing yield of NH3. However too low temperatures: reaction too slow (high Ea to break NN bond, not economically viable, 450C is optimum moderately high temp
Explain pressure condition for haber process
Increasing pressure shift eqm position to the right and increases yield of NH3, increase rate at which equilibrium is established
But cost of equipment to produce and maintain high pressure would be greater, 250atm is a compromise between yield and cost
Explain catalyst condition for haber process
To compensate for slower reaction at lower operating temp, iron catalyst is used to shorten time required to reach equilibrium, cheaper alternative
Why is there a need to remove NH3 formed in haber process
Shifts eqm position to the right, increasing yield
Reversible reaction definition
One that can go in both backward and forward directions
