Educational worksheet on physical and chemical changes featuring illustrated examples and multiple-choice questions.

Problem: Identifying Physical and Chemical Changes

The task involves distinguishing between physical changes and chemical changes. Here's a brief explanation of the two:

- Physical Change: A change in which the physical properties (e.g., shape, size, state) of a substance are altered, but its chemical composition remains the same. No new substances are formed.
- Chemical Change: A change in which the chemical composition of a substance is altered, resulting in the formation of new substances with different properties.

Now, let's solve each question step by step:

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1. Soured milk smells badly because bacteria have formed new substances in the milk. This is an example of:

- Explanation: When milk sours, bacteria break down lactose into lactic acid, forming new substances. This alters the chemical composition of the milk.
- Answer: b. chemical change

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2. Sand flowing in an hourglass is an example of:

- Explanation: The sand simply changes its position from one side of the hourglass to the other without any alteration in its chemical composition.
- Answer: b. physical change

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3. The change of state from a gas to a liquid is an example of:

- Explanation: Changing from a gas to a liquid involves a change in the physical state of matter (e.g., condensation), but the chemical composition remains the same.
- Answer: b. physical change

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4. Which is an example of a physical change?

- Options:
- a. closing the door
- b. cracking an egg
- c. turning off the electric light
- d. putting the milk back in the fridge
- Explanation:
- a. Closing the door: No chemical change occurs; it's a physical action.
- b. Cracking an egg: The structure of the egg changes, but no new substances are formed.
- c. Turning off the electric light: This is a change in energy state, not a chemical or physical change to matter.
- d. Putting the milk back in the fridge: The temperature of the milk changes, but its chemical composition remains the same.
- Answer: d. putting the milk back in the fridge

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5. The melting of butter when left out in a warm room is an example of:

- Explanation: Melting is a change in the physical state of butter from solid to liquid, but the chemical composition of butter remains unchanged.
- Answer: b. physical change

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6. Which of the following is an example of physical change?

- Options:
- a. closing the door
- b. cracking an egg
- c. turning off the electric light
- d. putting the milk back in the fridge
- Explanation:
- a. Closing the door: No chemical change occurs; it's a physical action.
- b. Cracking an egg: The structure of the egg changes, but no new substances are formed.
- c. Turning off the electric light: This is a change in energy state, not a chemical or physical change to matter.
- d. Putting the milk back in the fridge: The temperature of the milk changes, but its chemical composition remains the same.
- Answer: d. putting the milk back in the fridge

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7. An ice cream cone melting on a hot day is an example of:

- Explanation: Melting is a change in the physical state of the ice cream from solid to liquid, but the chemical composition remains unchanged.
- Answer: b. physical change

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8. Which of the following describes a chemical change?

- Options:
- a. water freezing
- b. match burning
- c. dew on grass
- d. magnetizing a nail
- Explanation:
- a. Water freezing: This is a physical change (change in state).
- b. Match burning: Burning involves combustion, which produces new substances (e.g., carbon dioxide and water).
- c. Dew on grass: This is a physical change (condensation).
- d. Magnetizing a nail: This is a physical change (change in magnetic properties).
- Answer: b. match burning

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9. Charcoal burning on the grill is an example of:

- Explanation: Burning charcoal involves combustion, where charcoal reacts with oxygen to produce new substances such as carbon dioxide and ash.
- Answer: b. chemical change

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Final Answers:

1. b. chemical change
2. b. physical change
3. b. physical change
4. d. putting the milk back in the fridge
5. b. physical change
6. d. putting the milk back in the fridge
7. b. physical change
8. b. match burning
9. b. chemical change

Boxed Final Answer:
\[
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\begin{array}{l}
1. \text{b} \\
2. \text{b} \\
3. \text{b} \\
4. \text{d} \\
5. \text{b} \\
6. \text{d} \\
7. \text{b} \\
8. \text{b} \\
9. \text{b} \\
\end{array}
}
\]