6. The Rate and Extent Of Chemical Change
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How do you work out rate?
Rate = quantity of reactants used / time or Rate = quantity of products used / time
What does the collision theory state?
In order for a chemical reaction to occur, particles must collide with sufficient energy
What is activation energy?
The minimum energy particles must have for a reaction to be successful
What happens as a reaction progresses?
The concentration of reactants decreases meaning the frequency of collisions between particles is reduced and so the reaction slows down
How is the rate of a reaction increased?
• particles must collide more frequently * particles must collide with more energy
How do you achieve a higher rate of reaction?
Increase pressure, temperature, or concentration
What is concentration?
The number of reactant particles in a given volume of liquid
Does increasing temperature increase the number of reacting particles?
No, it just increases the chance of successful collisions
Will the amount of product produced in the reaction be more, less, or the same at a higher temperature?
The same amount of product will be produced at all temperatures just at different rates
What is a catalyst?
A substance that changes the rate of reactions, but is not changed chemically itself at the end of the reaction
How do catalysts work?
• do not increase frequency of collisions or make collisions more energetic • do provide an alternate reaction pathway to the products with a lower activation energy
What is a reversible reaction?
Where the products of the reaction can react to produce the original reactants
How can reversible reactions be represented?
A + B equilibrium arrow symbol C + D
What does the double arrow on a reaction mean?
The reaction can go in either direction
What happens if a reversible reaction in exothermic in one direction?
It is endothermic in the other
What does it mean in a reversible reaction that the reaction is exothermic in one direction and endothermic in the other?
The energy absorbed in one direction is equal to the energy released in the other
What is an example of a reversible reaction?
Hydrated copper sulphate <> anhydrous copper sulphate + water
What always happens when a reversible reaction takes place in a closed system?
A state of equilibrium will be reached
What is equilibrium?
When the amounts of reactants and products reach a balance - their concentrations stop changing
What is a closed system?
When none of the reactants or products can escape
How are the rates of the forward and backward reactions in a state of equilibrium?
The rate of the forward reaction is equal to the rate of the backward reaction
Why are the conditions of equilibrium changed?
In industrial processes, to: • maximise yield • minimise cost • minimise environmental impact
What does the position of equilibrium depend on?
• temperature • pressure • concentration
What is Le Chatelier’s rule?
If a system is at equilibrium and a change is made to any of the conditions then the system responds to counteract the change