6. The Rate and Extent Of Chemical Change
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How do you work out rate?
Rate = quantity of reactants used / time (s) or Rate = quantity of products formed / time (s)
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/concentration, temperature, surface are or add a catalyst
What is concentration?
How many particles per unit of volume
as conc / pressure increases
more particle per unit of volume –> collisions are more frequent = increase rate of reaction
as temperature increases …
{ particles gain more energy –> move faster –> collide more frequently collide with more energy–> more likely to exceed activation energy } higher rate of successful collisions + reaction
Does increasing temperature increase the number of reacting particles?
No, it just increases the chance of successful collisions
as SA increases …
rate of reaction increases as higher SA : V ratio= more available sa for collisions = more frequent 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 speeds up a reaction, without being used up in the reaction itself
How do catalysts work?
activation energy is lowered more particles have more sufficient energy to successfully react
What is a reversible reaction?
Where the products of the reaction can react to produce the original reactants both forward and backward reactions can happen
How can reversible reactions be represented?
A + B ⇌ C + D
What is equilibrium?
When the amounts of reactants and products reach a balance - their is no overall change in conc. of reactants
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
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 (requires heat to work) 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 a closed system?
When none of the reactants or products can escape