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3.2.3 Equilibria
Energetics - Kinetics - Equilibria - Redox - Group VII - Group II - Metal Extraction - Haloalkanes - Alkenes - Alcohols - Analytical Tech... - Unit 1
3.2.3.1 Dynamic nature
3.2.3.2 Qualitative effects of factors
3.2.3.3 Industrial Processes
Self assessment
Practice Exam questions
3.2.3.2 Qualitative effects of factors
3.2.3.3 Industrial Processes
Self assessment
Practice Exam questions
3.2.3.1 Dynamic nature of Equilibria
Some reactions are reversible.
e.g. When we heat hydrated copper(II)sulphate it becomes white anhydrous copper sulphate; if we add water again we can reverse the process to obtain blue copper(II) sulphate again.
Some reactions are reversible.
e.g. When we heat hydrated copper(II)sulphate it becomes white anhydrous copper sulphate; if we add water again we can reverse the process to obtain blue copper(II) sulphate again.
Equilibrium
As the forward reaction slows down because reactants are being used up then backward reaction will speed up.
An equilibrium in a reversible reaction is when both the forward and reverse reactions are occurring simultaneously at the same rate. The concentration of reactants and products will remain the same but not necessarily equal.
When you change the reaction conditions the rate of one can change until a new equilibrium if reached; this is called dynamic equilibrium. N.B The reaction has not stopped.
As the forward reaction slows down because reactants are being used up then backward reaction will speed up.
An equilibrium in a reversible reaction is when both the forward and reverse reactions are occurring simultaneously at the same rate. The concentration of reactants and products will remain the same but not necessarily equal.
When you change the reaction conditions the rate of one can change until a new equilibrium if reached; this is called dynamic equilibrium. N.B The reaction has not stopped.
Conditions for Equilibrium
N.B Equilibrium can only be reached in a closed system. (One where the reactants and products cannot escape)
Equilibrium can be reached from either direction (the position of equilibrium can move).
Le Chatalier's Principle
If you change;
Concentration
Pressure
or Temperature
in a closed system, in a reversible reaction;
Then, the equilibrium will move to counteract the change.
N.B Equilibrium can only be reached in a closed system. (One where the reactants and products cannot escape)
Equilibrium can be reached from either direction (the position of equilibrium can move).
Le Chatalier's Principle
If you change;
Concentration
Pressure
or Temperature
in a closed system, in a reversible reaction;
Then, the equilibrium will move to counteract the change.
3.2.2.2 Qualitative affect of factors
If you increase the concentration of reactants then this will shift equilibria to the right (giving a higher yield).
If you increase pressure this will shift equilibrium towards the side with the fewer moles of gas.
If you increase temperature this will shift equilibrium towards the endothermic direction. (ΔH+)
If you decrease temperature this will shift equilibrium towards the exothermic direction. (ΔH-)
If we add a catalyst we increase the rate of reaction in both directions, leading to no equilibria change, though a system will reach equilibria faster because of the increased rate of reaction. (Catalysts provide an alternative route but the energy change is the same)
Worked Examples
If you increase the concentration of reactants then this will shift equilibria to the right (giving a higher yield).
If you increase pressure this will shift equilibrium towards the side with the fewer moles of gas.
If you increase temperature this will shift equilibrium towards the endothermic direction. (ΔH+)
If you decrease temperature this will shift equilibrium towards the exothermic direction. (ΔH-)
If we add a catalyst we increase the rate of reaction in both directions, leading to no equilibria change, though a system will reach equilibria faster because of the increased rate of reaction. (Catalysts provide an alternative route but the energy change is the same)
Worked Examples
If we increase the concentration of the reactants than the equilibria will shift to the right because there will be more successful collisions between reactants than products. This will increase the yield of the product.
If we increase the pressure then the equilibria will shift to the right because the are 2 moles of gas in the products and 3 moles of gas in the reactants (2+1), the equilibria moves to the side with fewest moles of gas and so oppose the change. This will increase the yield.
If we increase the temperature then the equilibria will shift towards the left side as this is the endothermic direction. The reaction act to lower the temperature of the system and so oppose the change. This will decrease the yield.
If we decrease the temperature then the equilibria will shift towards the right side as this is the exothermic direction. The reaction act to raise the temperature of the system and so oppose the change. This will increase the yield.
If we add a catalyst then the system will achieve equilibria sooner but will not shift equilibria in either direction and so not affect the yield.
If we increase the pressure then the equilibria will shift to the right because the are 2 moles of gas in the products and 3 moles of gas in the reactants (2+1), the equilibria moves to the side with fewest moles of gas and so oppose the change. This will increase the yield.
If we increase the temperature then the equilibria will shift towards the left side as this is the endothermic direction. The reaction act to lower the temperature of the system and so oppose the change. This will decrease the yield.
If we decrease the temperature then the equilibria will shift towards the right side as this is the exothermic direction. The reaction act to raise the temperature of the system and so oppose the change. This will increase the yield.
If we add a catalyst then the system will achieve equilibria sooner but will not shift equilibria in either direction and so not affect the yield.
If we increase the concentration of the reactants than the equilibria will shift to the right because there will be more successful collisions between reactants than products. This will increase the yield of the product.
If we increase the pressure then the equilibria will shift to the left because the are 2 moles of gas in the products and 1 moles of gas in the reactants, the equilibria moves to the side with fewest moles of gas and so oppose the change. This will decrease the yield.
If we increase the temperature then the equilibria will shift towards the right side as this is the endothermic direction. The reaction act to lower the temperature of the system and so oppose the change. This will increase the yield.
If we decrease the temperature then the equilibria will shift towards the left side as this is the exothermic direction. The reaction act to raise the temperature of the system and so oppose the change. This will decrease the yield.
If we add a catalyst then the system will achieve equilibria sooner but will not shift equilibria in either direction and so not affect the yield.
Exercise Try these two examples yourself;
If we increase the pressure then the equilibria will shift to the left because the are 2 moles of gas in the products and 1 moles of gas in the reactants, the equilibria moves to the side with fewest moles of gas and so oppose the change. This will decrease the yield.
If we increase the temperature then the equilibria will shift towards the right side as this is the endothermic direction. The reaction act to lower the temperature of the system and so oppose the change. This will increase the yield.
If we decrease the temperature then the equilibria will shift towards the left side as this is the exothermic direction. The reaction act to raise the temperature of the system and so oppose the change. This will decrease the yield.
If we add a catalyst then the system will achieve equilibria sooner but will not shift equilibria in either direction and so not affect the yield.
Exercise Try these two examples yourself;
3.2.2.3 Industrial processes
When using knowledge of equilibria to design industrial manufacturing processes it is not always possible to achieve ideal conditions. A compromise is often made. Reasons for this are;
High temperature in an exothermic reaction
When using knowledge of equilibria to design industrial manufacturing processes it is not always possible to achieve ideal conditions. A compromise is often made. Reasons for this are;
High temperature in an exothermic reaction
- A balance between a fast rate of reaction and a high yield
- To use lower pressure equipment / valves / gaskets / piping
- To use less expensive equipment to resist high pressure
- To lower power / energy required to provide high pressure / pumping
- safety factor with reason
- cost of high temperature / energy]
- cost of plant (to resist high T) too high
- plant could not contain high T
- Catalyst not used up so can be used again
- Reactants not used can be recycled (used again)
- Increase atom economy
- Reduce environmental effect (e.g. carbon dioxide)
- Reduce cost of raw materials
Self Assessment
Practice Exam questions
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Energetics - Kinetics - Equilibria - Redox - Group VII - Group II - Metal Extraction - Haloalkanes - Alkenes - Alcohols - Analytical Tech... - Unit 1