3.15 - kinetics & 3.16 - equilibrium
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What is the definition of activation energy?
The minimum energy required for reactant particles to collide and the reaction occurring
Why do not all reactions occur
• not enough activation energy • reactants not in the right orientation
What is the effect of concentration and pressure on ROR?
• more particles in a given volume • more frequent successful collisions • ROR increases
What is the definition of a catalyst?
a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount
How do catalysts work?
by providing an alternative reaction route of lower activation energy.
What are the conditions of an equilibrium ?
• rate of forward and backwards reactions are equal • concentrations of reactants and products are not changing
What is Le Chatelier’s principle?
When a factor is changed an equilibrium will shift to oppose that change
How does a catalyst effect the yield of a reaction?
No effect
How does pressure effect yield?
Increased pressure = increased yield
How does temperature effect yield?
Increased temperature = decreased yield
Affect on Yield - pressure (model answer) 3 marks
• the yield increases/decreases • because there are more/less moles on the left/right • therefore equilibrium shifts to oppose the increase/decrease
Affect on Yield - temperature (model answer) 3 marks
• the yield increases/decreases • because the forwards/backwards reaction is exo/endothermic • therefore equilibrium shifts right/left to oppose the increase/decrease in temperature
How do you know if a reaction is exothermic or endothermic
Exothermic: forward enthalpy change is - Endothermic: forward enthalpy change is +
How does pressure effect how the equilibrium shifts
DECREASE pressure: Equilibrium will shift to side with LESS moles INCREASE pressure: Equilibrium will shift to side with MORE moles
What factors effect Kc and Kp
ONLY temperature not pressure or catalyst
What’s the effect of a catalyst on Kp and why
No effect because it increases the rate of forwards and backwards reaction equally
How does adding more reactant effect Kp
No effect
Why might a catalyst become less efficient if there are impurities
Impurities may block the active sites
What happens to yield if pressure is changed but there are equal moles on both sides
Equal moles of gas in products and reactants so there is no change in yield
Why does the total volume of a mixture not need to be measured to allow a correct Kc value to be calculated
There are equal number of moles on each side of the equation
What does the area under a maxwell Boltzmann curve represent
Total number of particles
Why does a catalyst increase ROR
• lower activation energy means more particles will have energy greater than the activation energy
What is the impact of pressure used in an industrial process
• increasing pressure may give a higher yield and faster ROR • but expensive to produce due to higher energy costs and may be dangerous • after a certain point the increase in yield is minimal (when the curve starts to flatten)
What is the impact of temperature used in an industrial process
• low temperatures may give a higher yield • but slow ROR therefore the optimum temp needs to be a compromise between the ROR and yield