In this chapter of A2/A-Level Chemistry, , we will go through the Rates of Reactions.
Rates of Reactions
Reaction Rate = change in amount of reactants/products per unit time (units: mol dm-3s-1)
Following a reaction;
- gas volume produced (gas syringe)
- mass lost (balance)
- colour change (colorimeter)
- clock reaction (sudden change at particular time means specific concentration of product has been reached - the shorter the time taken, the faster the rate)
- electrical conductivity (number of ions will change as reaction occurs)
Concentration-Time Graph
Rate at any point can be found by drawing a tangent at that point on the graph and finding the gradient.
Orders of Reaction
In A2/A-Level Chemistry, the order of reaction = how the reactants concentration affects the rate
INCREASE REACTANT – RATE STAYS THE SAME – ORDER OF 0
INCREASE REACTANT – RATE INCREASES BY 1 FACTOR – ORDER OF 1
INCREASE REACTANT – RATE INCREASES BY 2 FACTORS – ORDER OF 2
*square brackets indicate concentration. For example [X] = concentration of X.
Half-life = time taken for half the reactant to react
If the half life is constant = first order
If the half life is doubling = second order
In A2/A-Level Chemistry, you can also calculate the half life using reaction rates. For example, if you’re given the rate constant (see below) and the order you can work out half life (you don’t need to know how, just to be aware of it)
That's how we describe the rate of reaction. Thanks for watching!