Rates and surface area to volume ratio
Dividing lumps
For a given The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of a solid, large lumps have smaller The total area of exposed material available for a chemical reaction (or absorption) to take place. to The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. ratios than smaller lumps or powders. If a large lump is divided or ground into a powder:
- its total volume stays the same
- the area of exposed surface increases
- the surface area to volume ratio increases
Lumps vs powders
The greater the rate of A collision between reactant particles that has enough energy for a reaction to happen., the greater the rate of reaction. If the surface area to volume ratio of a reacting solid is increased:
- more A substance that reacts together with another substance to form products during a chemical reaction.A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. are exposed at the surface
- the rate of collisions between reactant particles increases
- therefore the rate of reaction increases
Note that the mean The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. of the particles does not change. However, since the rate of collisions increases (they happen more often), the rate of successful collisions also increases.
Graphs
The rates of two or more reactions can be compared using a graph of mass or volume of A substance formed in a chemical reaction. formed against time. The graph shows this for two reactions.
- the horizontal line shows that no more product is being made - the reaction has finished
- the mass of product formed is not affected by the rate of reaction
The Another word for steepness. On a graph, the gradient is defined as being the change in the 'y' value divided by the change in the 'x' value. It defines how steep a line is. of the line is equal to the rate of reaction. The faster reaction with the powder:
- gives a steeper line
- finishes sooner