Reverse reactions and equilibrium Term 1 Flashcards
Define reverse reactions.
When products, once formed, can react again to form new reactants.
Examples of principle of reversibility
phase changes, dissolution of gases, precipitation and dissolution of ionic solids
Define an open system.
Matter and energy can be exchanged with the surroundings
Define a closed system
Energy can be exchanged with surroundings but matter can not
Define an irreversible reaction
When products cannot be converted back to reactants
What is the principle of reversibility
An elementary reaction can occur in both forward and reverse directions
Examples of reverse reactions
evaporation and condens., saturated sugar solution, reaction of haemoglobin
Describe reaction between haemoglobin and oxygen
reversible reaction
Describe evaporation and condensation reaction
reversible reaction
Describe saturated sugar reaction to form a solution
reversible reaction
Define dynamic equilibrium
A continual exchange
What must occur during equilibrium?
(x4)
-closed system
-rate of fwd and reverse reaction are =
-constant composition
-Kc value dependent on temperature
Difference between extent of reaction and rate of reaction
extent indicates how much product is formed at eqm where as rate is a measure of the change in concentration of the reactants and products with time
Equation for Kc
eqm constant
aA+bB—-><— cC+dD
k= [C]^c x [D]^d / [A]^a x [B]^b
Equation for Kc. Qc?
eqm constant
aA+bB—-><— cC+dD
k= [C]^c x [D]^d / [A]^a x [B]^b
same reaction can be used to find reaction quotant when reaction not at eqm
What is meant when reactant is favoured in relation to Kc value
value will be less than 1
What is LeChateliers principle
when a change is applied to a system in dynamic eqm the composition of the eqm mixture will alter in such a way as to counteract that change
What occurs to Kc when inert gas added
no change
What factors effect eqm and how
Concentration of reacs and prods
-Kc stays same
-eqm shifts
Pressure
-Kc stays same
-increase in pressure pushes reaction to side with less gas particles
Temperature
-Kc alters
-greater effect to endothermic
Define eqm yield
the amount of products present at eqm
Example of explaining equilibrium when subject to concentration increase
N2O4—>2NO2
- Forwards rate increases due to an increase in concentration of N204. The particles per unit volume increases therefore increasing the frequency of collisions per unit time.
- The concentration of NO2 has remained the same meaning a backwards reaction rate doesn’t change therefore there is a net forward reaction
- The concentration of N204 will decrease as consumed therefore the forwards rate decreases as there is less particles per unit volume. The concentration of 2NO2 will increase as N2O4 consumed so the rate of bwd reaction will increase
- Until rates are equal and eqm occurs
Example of explaining equilibrium when subject to pressure increase
2NO2—>N2O4
- Increase in pressure will cause an increase in gas particle sper unit volume. This will equal more collisions per unit time, therefore increasing the rate of successful collision. This means both rates of reaction increase for both reactions.
- Because 2NO2 has more gas molecules, the forwards reaction will be effect more by the increase in pressure, rate of forward reaction will increase more=net fwd reaction
- As 2NO2 used up, fwds rate will decrease. As more N2O4 is produced the rate of reverse reaction will increase
- Until eqm is reached
Example of explaining equilibrium when subject to temperature decrease (exothermic reaction in this case)
2NO2—>N2O4
- decrease in temperature=decrease in average kinetic energy of particles. This will decrease the frequency of successful collisions therefore decreasing both rates
- The endothermic reaction will decrease more, therefore the rate of bwd reaction will decrease more=net forward reaction
- As NO2 is consumed, fwd rate decreases, as N2O4 produced, bwd rate will increase
4.Until eqm is reached
How does decrease in volume effect equilibrium
- Pressure is inversely proportional to the volume of a container. Therefore, decrease volume will increase the pressure
- This will cause an increase in gas particles per unit volume equalling more collisions per unit time, therefore increasing the rate of successful collision. This means both rates of reaction increase for both reactions.
- The substance with more gas molecules, will be effected more by the increase in pressure, (in this case the reactant) so rate of forward reaction will increase more=net fwd reaction
- As recatant is used up, fwds rate will decrease. As more product is produced the rate of reverse reaction will increase
- Until eqm is reached
How does a catalyst effect reaction rate and equilibrium
- Works by providing alternative reaction pathway requiring less activation energy. The addition of a catalyst will lower the activation energy of both the fwd and bwd reactions.
- Due to this, there will be more successful collision per unit time, therefore increasing the rate of the the fwd and bwds reaction equally.
- There will be no change to the relative concentration of the products and reactants due to the equal rate so the position of equilibrium will not change.
4.Therefore the value of equilibrium constant will not change.
