Rates, concentration and pressure
The greater the frequency or rate of A collision between reactant particles that has enough energy for a reaction to happen., the greater the rate of reaction. If the The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present. of a reacting Mixture formed by a solute and a solvent. or the Force exerted over an area. The greater the pressure, the greater the force exerted over the same area. of a reacting gas is increased:
- the number of 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. in a given volume increases
- the particles become more closely packed
- 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.
If the concentration of solution is doubled, the number of particles in a given volume is doubled and so too are successful collisions in a given time.
Graphs
The rates of two or more reactions can be compared using a graph of The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). or 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. 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
- rate of reaction does not affect the total amount of product formed (but it is important that enough reactant is used, especially if low concentration)
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 at the higher concentration or pressure:
- gives a steeper line
- finishes sooner
