This worksheet helps students practice distinguishing between chemical and physical changes using common examples like rusting iron and dissolving sugar.

Problem: Identifying Chemical and Physical Changes

The task is to classify each of the given changes as either chemical or physical. Here's a breakdown of the solution:

#### Definitions:
- Chemical Change: A change in which new substances are formed, and the chemical composition of the starting materials is altered. Energy is often absorbed or released.
- Physical Change: A change in which the physical form or state of a substance is altered, but its chemical composition remains the same.

#### Analysis of Each Change:

1. Heating water into steam
- Explanation: Water (liquid) is heated and turns into steam (gas). The molecules of water are simply changing their state from liquid to gas without forming any new substances.
- Type: Physical Change

2. Milk going sour
- Explanation: Milk spoils due to bacterial action, which breaks down lactose into lactic acid and other compounds. New substances are formed.
- Type: Chemical Change

3. Dissolving sugar in water
- Explanation: Sugar dissolves in water, forming a homogeneous mixture. No new substances are created; it is just a change in the physical state.
- Type: Physical Change

4. Iron rusting
- Explanation: Iron reacts with oxygen and moisture to form iron oxide (rust). This is a chemical reaction that produces a new substance.
- Type: Chemical Change

5. Hydrochloric acid and sodium hydroxide reacting and forming salt and water
- Explanation: Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form sodium chloride (salt) and water. This is a neutralization reaction, and new substances are formed.
- Type: Chemical Change

6. Digesting food into nutrients
- Explanation: Digestion involves breaking down complex molecules in food into simpler molecules (e.g., proteins into amino acids, carbohydrates into sugars). New substances are formed.
- Type: Chemical Change

7. Melting ice into water
- Explanation: Ice (solid) melts into water (liquid). This is a change in the physical state of water without altering its chemical composition.
- Type: Physical Change

8. Acid rain dripping onto limestone and making carbon dioxide gas
- Explanation: Acid rain (containing sulfuric or nitric acid) reacts with calcium carbonate in limestone to produce calcium sulfate, water, and carbon dioxide gas. New substances are formed.
- Type: Chemical Change

9. Breaking a glass into pieces
- Explanation: Breaking glass into smaller pieces does not change the chemical composition of the glass; it only changes its physical form.
- Type: Physical Change

10. Hydrogen peroxide decomposing into oxygen gas and water
- Explanation: Hydrogen peroxide (H₂O₂) decomposes into water (H₂O) and oxygen gas (O₂). This is a chemical reaction that produces new substances.
- Type: Chemical Change

#### Final Classification:

| Number | Description | Type |
|--------|--------------------------------------------------|---------------|
| 1 | Heating water into steam | Physical |
| 2 | Milk going sour | Chemical |
| 3 | Dissolving sugar in water | Physical |
| 4 | Iron rusting | Chemical |
| 5 | Hydrochloric acid and sodium hydroxide reacting and forming salt and water | Chemical |
| 6 | Digesting food into nutrients | Chemical |
| 7 | Melting ice into water | Physical |
| 8 | Acid rain dripping onto limestone and making carbon dioxide gas | Chemical |
| 9 | Breaking a glass into pieces | Physical |
| 10 | Hydrogen peroxide decomposing into oxygen gas and water | Chemical |

Final Answer:

\[
\boxed{
\begin{array}{|c|l|c|}
\hline
\text{Number} & \text{Description} & \text{Type} \\
\hline
1 & \text{Heating water into steam} & \text{Physical} \\
2 & \text{Milk going sour} & \text{Chemical} \\
3 & \text{Dissolving sugar in water} & \text{Physical} \\
4 & \text{Iron rusting} & \text{Chemical} \\
5 & \text{Hydrochloric acid and sodium hydroxide reacting and forming salt and water} & \text{Chemical} \\
6 & \text{Digesting food into nutrients} & \text{Chemical} \\
7 & \text{Melting ice into water} & \text{Physical} \\
8 & \text{Acid rain dripping onto limestone and making carbon dioxide gas} & \text{Chemical} \\
9 & \text{Breaking a glass into pieces} & \text{Physical} \\
10 & \text{Hydrogen peroxide decomposing into oxygen gas and water} & \text{Chemical} \\
\hline
\end{array}
}
\]