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CER - Equilibria

OCR A level Chemistry A Chains Energy and Resources

What is it called when there is a balance between the reactants and the products? Equilibrium.
Where can a chemical equilibrium be achieved? A closed system where nothing can enter or leave.
Is the thermal decomposition of calcium carbonate reversible in an open system? No, because the CO2 escapes.
In an closed system, which direction of the thermal decomposition of CaCO3 is endothermic and which is exothermic? Forward: endothermic. Backward: exothermic.
What is a dynamic equilibrium? The rate of the forward reaction is equal to the rate of the reverse reaction, so the amount of each substance present does not change, even though the forward and reverse reactions are occurring.
What are the features of a dynamic equilibrium? Rate of forward reaction equal to rate of reverse reaction. Overall quantities of mixture remain the same. Occurs in a closed system. Can be established from either direction.
What is Le Chatelier’s Principle? The position of an equilibrium will shift so as to minimise the effect of any change in conditions.
What would happen in the thermal decomposition of CaCO3 if temperature was increased? More CaO and CO2 produced, and less CaCO3.
What would happen in the thermal decomposition of CaCO3 if the pressure was increased? Moves to side with lease moles of gas, so happens in reverse direction, producing more CaCO3 and less CaO and CO2.
What would happen in the thermal decomposition of CaCO3 if CO2 concentration was increased? Happens more in reverse direction to produce more CaCO3, leaving less CaO and CO2.
What is the equation for the Haber process? N2 + 3H2 (reversible) 2NH3
What are the operating conditions for the Haber process? 450°C; 150atm; catalyst of finely divided iron.
Why is temperature of 450 used? Forward reaction is favoured by low temperatures, but a compromise is needed between a reasonable yield and a reasonable rate.
Why is a pressure of 150atm used? Forward reaction is favoured by a high pressure, but a higher pressure would be too expensive (compromise between yield and expense).
Why is catalyst of finely divided iron used? Speeds up forward and reverse reactions equally, so allows the reaction to be carried out at a lower temperature, achieving a better yield of ammonia.
Created by: emm142