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A short class with Sarah and her students. The other ways are under More.
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Today, let's explore the burning of a candle. First, can anyone tell me what happens to the wax as the candle burns?
It melts!
Exactly! The melting of the wax is a physical change. Can anyone remind us what a physical change is?
It's when no new substance is formed and the change is usually reversible.
Perfect! So when the wax turns from solid to liquid, the physical properties change, but the wax itself remains the same substance. We can freeze it again and get solid wax.
So it’s temporary?
Yes! Remember the acronym 'CRISP': Change is Reversible, Involves Same substance, Physical properties change. This is helpful to recall the features of physical changes.
Got it!
Great! So the melting of candle wax is a clear example of a physical change.
Now let’s talk about the burning aspect of the candle. What happens when the wax burns?
It produces light and smoke!
Correct! Burning the wax produces light, heat, and smoke, which indicates a change is happening. What can we say about the change when the wax burns?
It's a chemical change!
Exactly! During this chemical change, new substances are formed such as carbon dioxide and water vapor. Can anyone think of how we can recognize a chemical change?
There’s usually a change in color or gas is produced!
Absolutely! Remember the acronym 'HEAT GLOWS' to remember that Heat, Evolution of gas, Altered colors, and a change in physical properties hint at a chemical change. So the burning of wax is a chemical change.
That makes sense!
Now that we understand both changes, let’s summarize why burning a candle is unique. Can anyone tell me how both changes are illustrated?
Well, first the wax melts, which is physical, and then it burns, which is chemical!
Exactly! Burning a candle is a fantastic illustration of both physical and chemical changes occurring simultaneously. What could this teach us about other situations?
It could show that some processes can involve both types of changes!
Right! So understanding these concepts helps us identify behaviors in various materials and their reactions. Always remember 'BOTH'—Burning has One Physical change and Two chemical changes.
That’s a good summary!
A transformation where no new substance is formed and the change is often reversible.
A process that leads to the creation of new substances with different properties.
The reaction of a substance with oxygen resulting in light and heat, and producing new substances.
When wax goes from solid to melt, that’s a physical change felt.
Imagine a candle at night, first it melts for a bright light, then it burns and creates new air, a chemical process in the night to share.
Remember BRIGHT: Burning Reaction Indicates Gas and Heat is Thermochange—signs of a chemical change.
Use the acronym HEAT to remember: Heat, Evolution of gas, Altered color, Transformation (signs of chemical change).
Term
Physical Change
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Term
Chemical Change
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Term
Combustion
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A substance used in candles that melts when heated.
A change that does not produce new substances and is usually reversible.
A change that results in the formation of new substances with different properties.
A chemical reaction involving the burning of a substance with oxygen.
This section explores the burning of a candle, highlighting both physical and chemical changes.
The activity of burning a candle illustrates the concept of physical and chemical changes, where the melting of the wax represents a physical change and the burning of the wax produces smoke and gases representing a chemical change.
In this activity, we examine the process of burning a candle as an illustrative example of both physical and chemical changes. When a candle burns, the wax first undergoes a physical change as it melts from solid to liquid. However, as the wax burns, it reacts with oxygen in the air, leading to a chemical change where new substances—carbon dioxide, water vapor, and smoke—are produced. This section emphasizes the dual nature of the changes occurring during the burning of a candle, noting the significance of understanding these transformations in daily life and scientific contexts.