OpenStax-CNX module: m20443
1
To investigate and discuss physical
and chemical changes in substances
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1 NATURAL SCIENCES
2 Matter, measuring and reactions
3 EDUCATOR SECTION
4 Memorandum
Examples of physical change:
a pan that is heated; tea that cools down
burning match; toasting bread
Examples of chemical change:
Marshmallow
• Yes, it tastes slightly dierent after being toasted
• Yes, it became black and powdery
• Chemical change. It is permanent - the chemical reaction changed the sugar to carbon.
Leaner Section
5 Content
5.1 ACTIVITY: To investigate and discuss physical and chemical changes in substances [LO
2.3]
People make use of dierent natural substances and change them into something else. To achieve this change,
substances are mixed with other substances, heated, separated, dissolved or treated with electricity. Some
changes are not permanent, while other changes cannot be reversed. We also distinguish between physical
and chemical changes.
Physical Change
When crystallised honey is heated in a pot it becomes uid again. But when it cools down and is exposed
to air, it will crystallise once more. No new substances are formed and the properties of the honey remain
exactly what they were. The change is a physical change. In the previous experiment, the orange/red
mercuric oxide became black when it cooled down (physical change).
Chemical change
∗ Version
1.1: Mar 16, 2009 2:49 am -0500
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http://cnx.org/content/m20443/1.1/
OpenStax-CNX module: m20443
2
When you pour pancake batter into warm oil, something happens: the appearance of the batter changes.
It is not runny any more, but sti. The change that occurs is permanent. A change that is permanent and
results in something new is a chemical change. The properties of the new substance dier from those of the
original substances. The mercuric oxide also experienced a chemical change when it was decompounded into
mercury and oxygen.
Name two further examples of physical and two examples of chemical change:
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Try the following:
Bring some marshmallows to school. Push them onto the prongs of a fork and heat them over a ame.
Answer the questions that follow.
• Taste a marshmallow (when it has cooled down). Has the taste changed?
• Has the appearance changed? Describe what you observe.
• Did this involve a physical or a chemical change? Motivate your ndings.
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Figure 1
6
7 Assessment
8
The learner will know and be able to interpret and apply scientic, technological
and environmental knowledge.
Assessment Standard 2.3: We know this when the learner interprets information by identifying key
ideas in text, nding patterns in recorded data, and making inferences from information in various forms
(e.g. pictures, diagrams, text).
Learning Outcome 2:
http://cnx.org/content/m20443/1.1/