Introduction to chemical reactions

• Chemical reactions make new chemicals.
• Atoms are rearranged during a chemical reaction, but the number of atoms does not change.
• Evidence of chemical reactions includes a large temperature change, bubbles, or a colour change.
• Chemical reactions can be represented using equations.

Watch this video to find out what happens to atoms in a chemical reaction.

Evidence for a chemical reaction can include any of the following:

• Bubbles – Many chemical reactions you see in the science lab make a chemical which is a gas, so you see bubbles.
• A colour change – If the new chemicals are a different colour from the original chemicals, there will be a colour change.
• A large energy change – Many chemical reactions give off lots of energy, like burning, and a few absorb energy, so they feel cold.

A new substance must be produced for a chemical reaction to take place.

The water inside a kettle has bubbles but that’s just because it is boiling. Bubbles of steam form in boiling water. These bubbles do not indicate a new substance has been formed because, when cooled, the steam condenses back into liquid water. Boiling is a physical change, not a chemical reaction.

• Lots of chemical reactions are used to make useful new chemicals, like plastics and medicines.

• Many useful chemical reactions involve burning fuels to release energy. These reactions heat our homes, power our cars and generate lots of the electricity that we use.

• Cooking uses chemical reactions to make foods which are safe and tasty to eat.

Watch this video about how a chef uses chemical reactions in their kitchen to make honeycomb.

If you mix vinegar and baking soda, a reaction will occur, where lots of bubbles of carbon dioxide gas form.

You can do this reaction at home but make sure you don’t get any of the chemicals in your eyes.Ethanoic acid is the chemical name for vinegar.Sodium bicarbonate is also known as baking soda.

In this animation, watch how sodium bicarbonate reacts with ethanoic acid.

Notice that…

• there are the same number of particles at the beginning of the reaction as there are after it
• the two reactants have broken down and reformed as three products
• sodium bicarbonate + ethanoic acid → sodium ethanoate + water + carbon dioxide

• Physical changes, such as melting, boiling and dissolving, do not make new chemicals. They are usually easy to reverse.
• In a chemical reaction, chemical bonds between atoms are broken and made, so the atoms get rearranged into new substances.
• The simplest kind of chemical reactions involve two elements reacting together to make a compound.

See what happens in the chemical reaction when iron and sulfur are heated. A sulfide is a chemical compound containing the element sulfur.

Types of data

If you carry out an investigation you will record evidence of any changes. The evidence you record is called data and it may be quantitative or qualitative.

Quantitative data

Quantitative data can be counted, measured, and expressed using numbers.

Quantitative data can be discrete (counted) or continuous (measured).

For example, if a reaction releases a lot of energy we can use a thermometer and measure the temperature rise in degrees Celsius ©.

Qualitative data (words)

Qualitative data describes qualities or characteristics which are often observable.

For example, “the colour changed from white to blue”.

You must always state what the colour was and what it changed too.

Data recorded in scientific experiments can be quantitative or qualitative.

Find out more about different types of data in science.

Looking for more resources for your chemistry lessons? In this video from the Chemistry Bites series, science presenter Jon Chase explains the Collision theory and four different ways to increase the rate of a reaction.

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