Temperature directly affects the rate of a chemical reaction. Raising the temperature causes the molecules to move faster and collide more often, which in turn increases the reaction rate.
Exercising precise temperature control during a reaction is particularly important during industrial-scale production and chemical manufacturing. For a start, it allows you to calculate the amount of reactant necessary to produce a certain volume of products in a set time. It can also help you determine how long it would take for a reaction to occur under certain temperature conditions. Many different types of chemical reactions and manufacturing procedures need to be performed at a precise temperature to achieve the optimum results.
Read on to learn more about how temperature affects the rate of a chemical reaction, as well as some of the other factors that can influence reaction rates.
In this post:
What are the factors affecting rates of reaction?
Different factors can affect the rate of a chemical reaction, some of which are outlined below. These factors can either be directly or inversely proportional to the rate of reaction.
- Temperature – as we explain later on, temperature is generally directly proportional to the rate of a reaction. As temperature increases, molecules gain more energy and move faster. This increases the chances of them colliding more often. However, this relationship has its upper limit, depending on the type of reactants involved. If the limit is reached, the reactants and the resulting products become too unstable.
- Concentration – the concentration of reactants also has a direct bearing on the rate of a reaction. The more concentrated the reactant is, the faster the reaction will occur. This is because there are more molecules available, which increases the likelihood of them bumping into each other.
- Surface area – solid reactants like wood tend to react more slowly because of their relatively small surface area. However, if you were to divide a solid block of a reactant into smaller pieces or turn it into powder, the reaction rate would increase as a larger surface area is exposed to other reactants.
- Catalysts – a catalyst is a substance that aids the rate of reaction but doesn’t participate in the chemical reaction itself. Although catalysts don’t chemically combine with the reactants, they provide the boost needed to allow the reaction to proceed. A catalyst can be an enzyme, an inorganic substance or a substrate like the interior surface of a catalytic converter.
How does the temperature affect the rate of a chemical reaction?
Before we explain how temperature affects the rate of a chemical reaction, it’s important to understand how a reaction works.
Chemical reactions occur when reactants’ molecules ‘collide’ with each other. This process both breaks down and creates new chemical bonds, resulting in the formation of new products. For chemical reactions to occur, the molecules must also have the minimum amount of kinetic energy (known as activation energy).
The amount of activation energy required varies depending on the type of reactants. Diesel combustion, for example, requires more activation energy than gasoline. This is where temperature comes into play.
Raising the temperature increases both the chances of effective collision and the level of activation energy. When the desired level of activation energy is reached, bonds are broken and elements or functional groups switch places or combine to form products more effectively.
How does decreasing the temperature affect the rate of reaction?
Generally, lowering the temperature slows down the rate of a reaction. This is because fewer molecules have the energy required to collide effectively with each other. In this case, the energy barrier (activation energy requirement) is not sufficiently breached to have a fast and sustained chemical reaction.
This applies to both simple inorganic and complex biochemical chemical reactions such as aerobic respiration. It’s also the main reason why freezing food slows down the decomposition process (cold temperatures reduce the metabolic rate of bacteria).
How to calculate the rate of a reaction
The rate of a chemical reaction is essentially the change in the mass of the reactants or products over time. The general formula can be therefore be written as:
Mass can be measured in various ways, including grams, molar mass, and non-metric units like pounds. However, the standard measure is molar mass because it’s easier to make precise calculations based on the molar weights of the chemicals involved.
What is the equation for rate of reaction?
The reactant side of the equation has a negative sign because the reactant is being diminished over time. Conversely, the sign on the product side is positive as the product increases over time. The formulas can therefore be written as:
The square brackets denote the concentration of the reactant or product. Again, this is typically expressed in terms of molar mass.
Various factors, such as the presence of a catalyst, surface area, concentration of reactants, and temperature can all affect the rate of a chemical reaction. However, temperature has the strongest direct proportional relationship with reaction rates. Raising the temperature increases the frequency of molecular collisions and therefore breaches the activation energy barrier.
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