📖 Reading Passage: Introduction to Chemical Reactions

A chemical reaction occurs when two or more substances interact to form new substances with different properties. During a chemical reaction, the atoms in the original substances (called reactants) rearrange to form new substances (called products). The total number of atoms remains the same, but they are arranged differently.

Chemical reactions are happening all around us every day. When you cook an egg, the heat causes proteins to change structure permanently. When iron rusts, it combines with oxygen from the air to form iron oxide. Even digesting food involves many chemical reactions in your body.

There are several main types of chemical reactions:

1. Combustion reactions: A substance burns in oxygen, producing heat and light. Example: methane burning in a gas stove.

2. Synthesis reactions: Two or more simple substances combine to form a more complex substance. Example: hydrogen and oxygen combining to form water.

3. Decomposition reactions: A complex substance breaks down into simpler substances. Example: water breaking down into hydrogen and oxygen using electricity.

4. Precipitation reactions: Two solutions mix to form a solid that settles out. Example: mixing silver nitrate and salt water to form solid silver chloride.

Signs that a chemical reaction has occurred include: colour changes, temperature changes, gas production (bubbling), formation of a precipitate (solid), or the release of light or sound.

🧪 Part 1: Multiple Choice Questions

✏️ Part 2: Short Answer Questions