Year 8 Science — Physical and chemical changes
Decide whether a change has made a new substance or merely rearranged an old one, say what combustion needs, and name the slow changes that turn rock into soil.
Name: ________________________
Before you start
Look closely at a burning candle. Two different kinds of change are going on at once.
- 1. The flame
- 2. The wick
- 3. The pool of melted wax
- 4. The solid wax of the candle
The wax melting into a pool, being drawn up the wick and turning to vapour are physical changes — it is still wax. Inside the flame, that vapour burns and becomes something else. That part is a chemical change.
1.Which statement describes a physical change?
- a) The state of a substance may change, and no new substance is formed
- b) A substance with different properties is formed
- c) A chemical reaction takes place and gives out heat
- d) The change is impossible to reverse
2.Combustion needs three things at the same time. Which set is right?
- a) A fuel, carbon dioxide, and sunlight
- b) A fuel, water, and a flame
- c) Oxygen, heat, and a container to hold the fire in
- d) A fuel, oxygen, and heat enough to reach the ignition temperature
3.Sand that a river carried settles on the riverbed, and over thousands of years it becomes rock. What does the chapter say about undoing changes like that?
- a) They can be reversed, but just in a laboratory
- b) They can be reversed by grinding the rock back to sand
- c) They reverse themselves each rainy season
- d) They cannot be reversed
4.Rock, pebbles and soil are picked up by wind or flowing water and carried somewhere else. What is that process called?
5.A black basalt rock exposed to damp air for a long time grows a red layer on its surface. What kind of change is that?
- a) A chemical change — iron in the rock has turned into iron oxide
- b) A physical change — the surface has been worn smooth by rain
- c) Neither — the rock was red underneath a black coating from the start
- d) A physical change — the red is dust that has settled and stuck
6.Sort each change by whether a new substance was formed.
Groups: Physical change · Chemical change
- Folding paper into a shape
- Adding baking soda to vinegar
- Burning a magnesium ribbon
- Cooking food
- Rusting of an iron nail
- Melting an ice cube
- Crushing chalk into powder
7.A candle burns. Which kinds of change are going on?
- a) Neither, because the candle is just getting shorter
- b) Chemical alone, because a flame is a chemical reaction
- c) Both — the wax melting and evaporating are physical, and the vapour burning is chemical
- d) Physical alone, because the wax is still wax the whole way through
8.Someone's clothes catch fire and a woollen blanket is wrapped around them. Why does that put the fire out?
- a) It soaks up the fuel that is feeding the flames
- b) It cools the clothes below their ignition temperature at once
- c) It cuts off the supply of air, so the burning has no oxygen
- d) It reflects the heat back onto the fire and smothers it with light
Answer key — Year 8 Science — Physical and chemical changes
- 1. a) The state of a substance may change, and no new substance is formed
- 2. d) A fuel, oxygen, and heat enough to reach the ignition temperature
- 3. d) They cannot be reversed
- 4. erosion
- 5. a) A chemical change — iron in the rock has turned into iron oxide
- 6. Melting an ice cube → Physical change; Crushing chalk into powder → Physical change; Folding paper into a shape → Physical change; Rusting of an iron nail → Chemical change; Burning a magnesium ribbon → Chemical change; Adding baking soda to vinegar → Chemical change; Cooking food → Chemical change
- 7. c) Both — the wax melting and evaporating are physical, and the vapour burning is chemical
- 8. c) It cuts off the supply of air, so the burning has no oxygen