Rates of reaction

• The rate of a reaction is a measure of how quickly a reactant is used up, or a product is formed.
• For a chemical reaction to happen, reactant particles must collide with each other, and the particles must have enough energy for them to react.
• A collision that produces a reaction is called a successful collision.
• The activation energy is the minimum amount of energy that colliding particles must have for them to react.
• The capacity of a system to do work or the quantity required for mechanical work to take place is measured in joules (J).
• The activation energy is different for different reactions.
• The method chosen for measuring the rate of a chemical reaction usually depends on the reactants and products involved, and how easy it is to measure changes in them.
• The mean rate of reaction can be calculated using either of these two equations: mean rate of reaction = quantity of reactant used/time taken or mean rate of reaction = quantity of product formed/time taken.
• Mass is measured in kilograms (kg) or grams (g) and the amount of matter an object contains.
• The change in mass can be followed during a reaction.
• This method is useful when carbon dioxide is a product which leaves the reaction container.
• This method is not suitable for hydrogen and other gases with a small relative formula mass.
• The sum of the relative atomic masses of the atoms in a chemical formula is known as relative formula mass, M r.
• The units for rate are usually g/s or g/min.
• The change in volume can be followed during a reaction.
• This method is useful when a gas leaves the reaction container.
• The volume of a gas is measured using a gas syringe, or an upside down burette.
• The units for rate are usually cm 3 s -1 or cm 3 min -1.
• The rate of reaction can be analysed by plotting a graph of mass or volume of product formed against time.
• The steepness of a line on a graph is defined as the change in the 'y' value divided by the change in the 'x' value, and the gradient is equal to the rate of reaction.
• The rate of a chemical reaction can also be measured in Mol s -1.