Unit B Lesson 3: Physical and Chemical Change
Completion requirements
Unit B Lesson 3: Physical and Chemical Change
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Learning Targets |
Big Question: How do I determine if a change is physical or chemical?
Matter can change in different ways. Look for evidence to decide what type of change has occurred.
Matter can change in different ways. Look for evidence to decide what type of change has occurred.
At the end of this inquiry, you should be able to answer the following questions:
- What constitutes a physical change?
- List the possible evidence of a chemical change.
- What are three chemical properties?
- What is a chemical reaction?
Page 105 in your text will help you answer these questions about physical and chemical change.
Introduction
Have you ever been to an aerial fireworks show and wondered how all the impressive colours are produced?
Understanding how fireworks produce various colours requires an understanding of chemical reactions. In this lesson, you will learn how chemical changes and chemical reactions are important aspects of life.
Physical and Chemical Change
Change is everywhere around us. Heraclitus, a Greek philosopher, said, βThe only thing that is constant is change.β Outside, the weather shifts from cold to warm or from winter to spring. The appearance of the moon from the earth changes from a crescent moon to a half moon to a full moon.
Matter is changing constantly, too. For example, wood rots, snow melts, cookies crumble, fireworks explode, cake becomes light and fluffy in the oven β the list is almost endless.
A physical change occurs when a change in the form or the state of the substance occurs, but the chemical composition of the substance remains the same.
How can you determine if a physical change has occurred?
Understanding how fireworks produce various colours requires an understanding of chemical reactions. In this lesson, you will learn how chemical changes and chemical reactions are important aspects of life.
Physical and Chemical Change
Change is everywhere around us. Heraclitus, a Greek philosopher, said, βThe only thing that is constant is change.β Outside, the weather shifts from cold to warm or from winter to spring. The appearance of the moon from the earth changes from a crescent moon to a half moon to a full moon.
Matter is changing constantly, too. For example, wood rots, snow melts, cookies crumble, fireworks explode, cake becomes light and fluffy in the oven β the list is almost endless.
A physical change occurs when a change in the form or the state of the substance occurs, but the chemical composition of the substance remains the same.
How can you determine if a physical change has occurred?
Watch
Watch the following videos to learn about physical properties and physical changes.
Look at the examples below and decide whether each situation illustrates the occurrence of a physical change:
(a) Chocolate mix dissolving into to milk
The hot chocolate mix dissolved in the hot milk to form a solution. The form of the hot chocolate and milk has changed, but the chemical composition of both substances has not changed.
(b) Dropping a plate that shatters
The
plate is still a plate.
A change in form
has occurred, which indicates a physical change.
(d) Beating eggs
The form of the eggs has changed now that they are beaten; however, the chemical composition of the eggs has not changed.
(e) Mowing grass
The grass is sorter than it was, so the form of the grass has changed.
(f) Sharpening a pencil
Some of the pencil is shaved off. The form of the pencil has changed; therefore, a physical change has occurred.
(g) Solidifying melted wax
A phase change has occurred
(liquid --> solid).
(liquid --> solid).
(i) Sublimation of dry ice
A phase change has occurred
(solid --> gas).
(solid --> gas).
Chemical Change
A chemical property can be observed if a chemical change occurs. A chemical change occurs when two or more materials react to produce a new substance.
In a chemical change...
Evidences of a Chemical Reaction
When a chemical reaction occurs, one or more of the following events occur:
A chemical property can be observed if a chemical change occurs. A chemical change occurs when two or more materials react to produce a new substance.
In a chemical change...
- A new substance is formed.
- The products have different characteristics and compositions from the starting materials.
Evidences of a Chemical Reaction
When a chemical reaction occurs, one or more of the following events occur:
- Colour change
- Gas produced
- Heat absorbed (endothermic) or released (exothermic) (although some physical changes can also include a temperature changes)
- Light produced
- Precipitate (solid) formed
- Irreversible (some chemical reactions are reversible but most are not)
- New substance formed
Watch
Watch the following video to learn more about chemical properties and changes.
Examples of chemical changes:
a. Burning paper
Evidence that a chemical reaction occurred:
- heat released (exothermic)
- light given off
- smell produced
- change in colour (white to black)
b. A tomato ripens
Evidence that a chemical reaction occurred:
- change in colour (green to red)
c. Fireworks exploding
Evidence that a chemical reaction occurred:
- heat released
- light given off
- smell produced
- change in colour
d. An egg is cooked
Evidence that a chemical reaction occurred:
- heat is absorbed (endothermic)
- change in smell
- change in colour
e. Rusting of iron
Evidence that a chemical reaction occurred:
- precipitate (solid rust) formed
- change in colour from black to rust
f. Vegetable scraps compost
Evidence that a chemical reaction occurred:
- change in smell (very stinky)
- change in colour
- (Vegetables are colourful.
- Compost is dirt colour.)
How can I tell if a physical or chemical change has occurred?
When a piece of paper is cut up into small pieces, it still is paper. This is a physical change in the form (shape and size) of the paper. However, if the same piece of paper is burned, it is changed into various substances that are not paper. Burning the paper is a chemical change.
When a piece of paper is cut up into small pieces, it still is paper. This is a physical change in the form (shape and size) of the paper. However, if the same piece of paper is burned, it is changed into various substances that are not paper. Burning the paper is a chemical change.
Physical changes can be reversed, but most chemical changes cannot be reversed.
For example, a cup of water can be frozen when cooled and then returned to a liquid form when heated. If a piece of paper is burned, no one can reverse the reaction.
If sugar is mixed into water to make sugar water, the change is physical because the water could be left to evaporate and the sugar crystals would remain. However, if a mixture of flour, water, sugar, and other ingredients are baked, some extraordinary means would be needed to separate the various ingredients into their original forms. Mixing the ingredients of the cake is a physical change, but baking the cake produces a chemical change.
For example, a cup of water can be frozen when cooled and then returned to a liquid form when heated. If a piece of paper is burned, no one can reverse the reaction.
If sugar is mixed into water to make sugar water, the change is physical because the water could be left to evaporate and the sugar crystals would remain. However, if a mixture of flour, water, sugar, and other ingredients are baked, some extraordinary means would be needed to separate the various ingredients into their original forms. Mixing the ingredients of the cake is a physical change, but baking the cake produces a chemical change.
Try It!
Practice Worksheet: Physical and Chemical Changes
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
- DOWNLOAD this practice worksheet (S9_UB_S1_L3a_physical_chemical). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
- As you watch the video below, "Physical and Chemical Changes", complete the worksheet.
- When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
Chemical Properties
Chemical properties can be seen only when a chemical reaction occurs. Some examples of chemical properties of matter are:
Examples of these chemical properties in action are shown in the videos below:
Chemical properties can be seen only when a chemical reaction occurs. Some examples of chemical properties of matter are:
- reaction with acids
- ability to burn
- reaction with water
Examples of these chemical properties in action are shown in the videos below:
Magnesium reacts with hydrochloric acid.
Many substances burn (combustion) in the presence of oxygen.
The reaction of copper with nitric acid.
Sodium reacts with water. Watch the "Sodium vs. Water" (slow motion) video.
Try It!
Practice Worksheet: Properties of Matter
-
DOWNLOAD this practice worksheet (UB_S1_L3b_properties_of_matter). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
- As you view the video below, "Properties of Matter - Physical and Chemical Properties", list the pieces of evidence for each chemical reaction on the practice worksheet.
- When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't
view the suggested answers first. This practice work is not for marks,
it is meant to help you check your understanding. Check the answers
AFTER doing the questions! Keep the practice worksheet for study
purposes. If you don't understand something, contact your teacher!
