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Signs of Reaction

In this worksheet, students will answer questions on chemical reactions and what to look for to indicate that a reaction is taking place.

'Signs of Reaction' worksheet

Key stage:  KS 3

Curriculum topic:   Chemistry: Chemical Reactions

Curriculum subtopic:   Types of Chemical Reactions

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

When a chemical reaction takes place, there are several changes that may occur. These visible changes are called the indicators of a chemical reaction. There are several indicators of reaction:

  

colour change when chemical is added to a flask of solution

 

Colour Change

 

A change in colour is a sign of a chemical reaction. For example, frying an egg is a chemical reaction with a colour change - colourless to white.

 

 

TReaction giving off gas

Gas Given Off  

 

During a chemical reaction, a gas can be produced. This can be seen by bubbles forming in the reaction or by a coloured gas being produced (such as smoke).

 

 

Precipitate forming

Solid Formed  

 

If two solutions are mixed and a solid is formed, this is called a precipitate. A precipitate is an insoluble solid formed by reacting two liquids. For example, when milk goes very sour, a solid is formed.

 

 

Match burning

Temperature Change 

 

An energy change involves a change in temperature (either up or down). For example, the burning of a match involves a release of both heat and light.

 

 

The indicators of chemical reactions shown here all involve a chemical change - for example, the burning of a match. These are different to physical changes (such as boiling water) which always end up with the same substance, but sometimes in a different state (liquid to gas); it's easy to confuse those with a chemical reaction. which always ends up with new substances, so watch out!

 

Remember that, in a chemical reaction, one or more new substances are produced!

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