This worksheet helps students distinguish between physical and chemical changes using everyday examples like melting butter and souring milk.

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 the 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:

- Answer: b. chemical change
- Explanation: When milk sours, bacteria break down lactose into lactic acid and other compounds. This process creates new substances, indicating a chemical change.

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

- Answer: b. physical change
- Explanation: The sand simply changes its position from one side of the hourglass to the other. There is no change in the chemical composition of the sand, so this is a physical change.

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

- Answer: b. physical change
- Explanation: Changing the state of matter (e.g., gas to liquid) involves a change in physical properties (e.g., temperature and pressure) but does not alter the chemical composition of the substance. This is a physical change.

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4. Which is an example of a physical change?

- Options:
- a. blowing out candles on a birthday cake
- b. burning wood in a campfire
- c. baking bread
- d. cutting a piece of bread
- Answer: d. cutting a piece of bread
- Explanation:
- a. Blowing out candles involves combustion, which is a chemical change.
- b. Burning wood produces ash and smoke, indicating a chemical change.
- c. Baking bread involves chemical reactions that create new substances.
- d. Cutting a piece of bread only changes its shape, which is a physical change.

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

- Answer: b. physical change
- Explanation: Melting is a change in the state of matter (solid to liquid) without altering the chemical composition of the butter. This is a 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
- Answer: d. putting the milk back in the fridge
- Explanation:
- a. Closing the door is a mechanical action, not a physical or chemical change.
- b. Cracking an egg involves breaking the shell, which is a physical change, but the question asks for the best example among all options.
- c. Turning off the electric light involves electrical processes, not a physical or chemical change.
- d. Putting the milk back in the fridge cools it down, changing its temperature but not its chemical composition, making it a physical change.

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

- Answer: b. physical change
- Explanation: Melting is a change in the state of matter (solid to liquid) without altering the chemical composition of the ice cream. This is a 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
- Answer: b. match burning
- Explanation:
- a. Water freezing is a change in state (liquid to solid), which is a physical change.
- b. Match burning involves combustion, producing new substances like carbon dioxide and water, which is a chemical change.
- c. Dew on grass is condensation, a physical change.
- d. Magnetizing a nail alters its magnetic properties but does not change its chemical composition, so it is a physical change.

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

- Answer: b. chemical change
- Explanation: Burning charcoal involves combustion, where charcoal reacts with oxygen to produce carbon dioxide and heat. This process creates new substances, indicating a chemical change.

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Final Answers:

1. b. chemical change
2. b. physical change
3. b. physical change
4. d. cutting a piece of bread
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:
\[
\boxed{
\begin{array}{l}
1. \text{b} \\
2. \text{b} \\
3. \text{b} \\
4. \text{d} \\
5. \text{b} \\
6. \text{d} \\
7. \text{b} \\
8. \text{b} \\
9. \text{b} \\
\end{array}
}
\]