The rate or speed of a reaction can measure how much product is being formed in a specific time.
The rate of a reaction can change as a result of changes in temperature, concentration, pressure and the presence of catalysts.
Some of the basics to consider when looking at chemical reactions is that a reaction is only able to occur if reactant particles collide with enough energy (activation energy) and that the more frequently particles collide, the greater the proportion of collisions with enough energy and therefore the greater the rate of reaction.
All making sense so far. So let’s look at some other factors to consider when discussing chemical changes.
Increasing the concentration or pressure of reactants in a solution increases the reaction rate, because more reacting particles are present in the same volume.
As we mentioned to begin with, for a reaction to happen, particles (atoms, ions or molecules) must collide with enough energy (the activation energy) to react. This is known as collision theory. The more crowded together the reactant particles are, the more collisions will occur per unit time.
Temperature is also able to impact the rate of a reaction. If the temperature of a reaction increases, this in turn increases the rate of the reaction as particles are able to collide with more energy.
In many cases a catalyst can also be added to a reaction to speed up the process. A catalyst is a substance which increases the rate of a chemical reaction without being chemically altered itself. Catalysts are often precious metals such as gold and platinum.
Catalysts reduce the amount of fossil fuels used up and prevent the release of carbon dioxide when they are burned.
Catalysts are often used in the form of powders or pellets. This is because they have a high surface area. The particles inside a large lump of solid cannot collide with surrounding particles, so fewer reactions occur. However, in a powder, where the surface area is much larger, more particles of the solid can collide with other reacting particles, so the reaction takes place more quickly.
There are two general methods which we can use to measure the rate of a reaction. How quickly the reactants are used up to make products and how quickly the products are formed from the reactants.
Measuring the mass of the reacting mixture is an example of technique number one. It is only possible when one of the products is a gas. Technique number two can be measured by measuring the volume of gas produced if one of the products is a gas, or by measuring a solid precipitate being formed if one of the products is a solid precipitate.
If a reaction has an inverse relationship, this means that as the time increases, the rate decreases.