What Kind Of Reaction Do You Call That?
Reactions are happening all the time in everyday life. For example, boiling an egg or baking a cake. These are all examples of chemical reactions. Whereas if you see a rusty nail or a rotten apple, these are the results of less appetising reactions. There are also reactions that are exciting to watch, such as creating a home-made volcano using baking soda and vinegar to produce CO2… and fireworks!
Discover more about the different types of chemical reactions and how you can speed up the rates that they happen…
5 Types of reactions
Find out if your class can name the types of reactions first and start the lesson off with a quick-fire pop quiz!
Synthesis → When two substances are combined to make a new substance or ‘compound’. An example of a synthesis reaction is when sodium (a highly-reactive metal) and chlorine (a poisonous gas) are mixed to create a new substance, sodium chloride (table salt). While salt is safe to consume as part of a healthy diet plan, it is neither a highly-reactive metal or poisonous gas you’re putting on your plate of chips.
Decomposition → Unlike a synthesis reaction, when two substances are mixed to form a new substance, a decomposition reaction separates a complex substance to break it down into two different substances. There are three main types of decomposition reactions: Thermal (using heat to separate the substances), Electrolytic (when an electric current passes through it, usually in a liquid solution) and Photo decomposition (when substances react when exposed to photons or light).
Combustion → When a compound is mixed with oxygen to form water and carbon dioxide. Combustion has a faster rate of reaction which produces a lot of heat energy. The most common examples are: when wood or coal is burned to create heat (in a stove, BBQ grill or fireplace), burning petrol or diesel to power a vehicle… and fireworks!
Displacement → When one or more compounds remove a substance from another compound. This reaction can occur as a Single Displacement (one substance is removed) or a Double Displacement (when two substances are “swapped” – when positive and negative ions switch places to form two new substances).
Photochemical → When light or photons are used to initiate a chemical reaction. In nature, photochemical reactions occur when sunlight is converted into good energy for plants during photosynthesis. In chemistry, a prime example of a photochemical reaction is photography. Here, silver chloride is broken down to form metallic silver on the photographic paper when exposed to light to create the photographic image.
It’s important to know that not all chemical reactions occur at the same rate. Some happen very quickly, like explosions and volcanic eruptions. Other reactions can happen over a longer period of time, such as souring milk or rusting metal. It is the speed of the reactants turning substances into products that we call the reaction rate.
For a chemical reaction to happen, the reactant particles must collide with each other, which is referred to as the Collision Theory. If a collision results in a reaction, this is known as a successful collision. For a collision to be successful, the reactant particles must have enough energy to initiate the reaction – or ‘activation energy’ (the minimum amount of energy required for a successful collision).
The reaction rate can also be changed by using a catalyst to speed up the reaction or an inhibitor to slow it down. Adding energy, such as heat, sunlight or electricity to a reaction can significantly increase the reaction rate. If you increase the concentration of the substance or the pressure of the reactants, this affects the reaction rate too.
Important Reaction Terms
Reactants → Reactants (also referred to as reagents) are the substances that are used to bring about the chemical reaction. A reactant is any substance that is consumed or used up during the reaction.
Products → The substance that is produced by a chemical reaction is called the product.
Catalyst → Sometimes a third substance is used in a chemical reaction to speed up or slow down the reaction. Enzymes are natural catalysts, which copy genetic material and break down food and nutrients in the body.
Inhibitors → An inhibitor is used to slow down the reaction. Examples of these are corrosion inhibitors, preservatives and UV stabilisers which are ideal to control the rate of reaction too.
Here are two interactive ways in which you can test the rate of reaction using heat (catalyst) and Alka Seltzer (reactant).
DON’T FORGET: #1 will get messy and #2 requires adult supervision!
TEST #1: For teachers to show the class:
1. Fill four transparent, open-topped bottles halfway with different water temperatures, varying from cold to hot.
2. Add a few drops of food colouring to each bottle of water – each one with a different colour to make the bottles easier to identify – and move the bottles around into a random order.
3. Add Alka Seltzer tablets to each bottle at approximately the same time and ask your students to watch the reactions.
4. Get your students to write down which temperature range of the bottles from cold to hot, identifying which bottle contains the coldest water and which bottle contains the hottest.
TEST #2: For your students to try themselves:
1. Fill half of one transparent bottle with cold water and fill half of a second transparent bottle with hot water. Remember to label each bottle COLD or HOT.
2. Carefully place an Alka Seltzer tablet inside a deflated balloon and attach the opening of the balloon to the open top of the first bottle, so it is securely hanging to one side. Repeat step for the second bottle.
3. Once both balloons are attached to the bottles, lift the balloon vertically to squeeze out the Alka Seltzer tablet from inside the balloon so it can fall inside the bottle to mix with the water. Repeat this step for the second bottle.
4. Watch the Alka Seltzer react to the water and inflate the balloon.
5. Record your results and explain why you think one reaction was faster than the other.
Teachers, why not video the experiments and share them on your school website?
To understand more, help bridge education gaps and to make remote learning as fun as possible, we want to support teachers (and parents too!) with Empiribox @ Home. This includes access to a vast library of KS1 and KS2 curriculum-aligned science resources for students – including interactive videos, worksheets, quizzes, adapted hands-on experiments and more! – whether they’re learning at home or in the classroom.
From all of us at Empiribox, we hope this helps teachers, students and parents to stay safe and engaged during these unique times.