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| Question | Answer |
| Key Feature of Physical Change. | no new substance is produced during the change. |
| What happen when solid/liquid/gas is heated? | The particles expand. |
| What happens when expansion occurs? | The volume of object increases and its density decreases. |
| What happens when contraction occurs? | The volume of substance decreases and its density increases. |
| What happen in thermometers? | It use expansion and contraction of liquid such as ethanol and mercury. As temperature increases, the liquid in the thermometer expands and moves up the thermometer. As it decreases, the liquid contracts and move down. |
| Solid to liquid | melting |
| Liquid to gas | evaporation |
| Gas to liquid | condensation |
| Liquid to solid | freezing or solidification |
| Solid to gas | sublimation |
| Gas to solid | deposition |
| What is melting? | When solid is heated enough, it melts and change into a liquid. i.e: butter spreads on a hot toast, the butter melts and soaks into the bread. |
| What is freezing? | The reverse process of melting. Freezing is when a liquid is cooled enough, it will form a solid. i.e: drops of liquid candle wax cool and become solid enough. |
| What is evaporation? | When a liquid is warmed and become a gas. It occurs a the surface of liquid at all temperatures but becomes faster as the temperature of the liquid increases. |
| What happens when liquid is at its boiling point? | Bubble of gas will form within the liquid and the liquid is said to be boil. |
| What is condensation? | When gas cools and becomes liquid. i.e: A cold can is left out of the fridge. It develops moisture on the outside. This is because water vapour in the air condenses on the cold outside of the can to form liquid water. |
| Explain why do you see fogs. | Fog is water vapour in your breath condensing to for a mist of tiny liquid water droplets. |
| Is mixing a physical change? | Yes, as long as no new substance is formed. |
| Explain how dissolving works. | When solute dissolves in solvent, they form a solution. Solute seems to disappear within the solvent. However, the solute broke down into such small particles that they are invisible. |
| What happens when solvent is removed? | If solvent is removed either by boiling or evaporation, then the solute particles join together again to form crystals. This process is known as crystallization. |
| Identifying a chemical change | 1. seeing bubbles or smelling a gas 2. seeing a change in colour 3. seeing a new solid (precipitate) 4. seeing light or feeling a change in temperature |
| Give an example that physical and chemical change occurs in the same time | Toasting bread starts as a physical change, heat evaporates water from the bread, drying i out. The drying bread starts to burn, changing colour to brown then black. This is a chemical change. |
| How is changing colour is a chemical change? | New substance produced by the chemical change has a different colour to what you started with. i.e: dyeing clothes or hair, bruised leg and ripening apple. |
| Why is mixing blue paint and yellow paint isn't a chemical change even though the colour changed to green? | This is because no new substances are formed. The yellow and blue paints particles are mixed so closely together that they give the illusion of green paint. |
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