Chemical reactions, Year 7: more practice：全部卡片
整套按顺序列出——孩子看到之前，您可以先通读一遍。
- Water boiling in a pan is full of bubbles. Why is this not a chemical reaction?
The bubbles are just water turning to steam, so no new substance forms
提示What is the gas in there, and where did it come from?
为什么Boiling is a change of state, a physical change. Steam is still water, so there is no new substance, which would be the sign of a chemical reaction.
- Bread dough bakes and its crust turns brown. Does the colour change suggest a chemical reaction?
Yes, a new colour suggests new substances have formed
提示Can the crust be turned back into dough?
为什么The browning of the crust is made by new substances, and it cannot be undone. Unexpected colour changes are a sign of a chemical reaction.
- A fizzing reaction gives off a gas that relights a glowing splint. Which gas is it?
Oxygen
提示Only one gas makes a glowing splint burst into flame again.
为什么Oxygen supports burning, so a glowing splint relights in it. It is the standard test for oxygen.
- Which gas turns limewater cloudy?
Carbon dioxide
提示The limewater reacts with the gas to form a fine white solid.
为什么Limewater turns cloudy because carbon dioxide reacts with it and makes tiny solid particles. This is the standard test for carbon dioxide.
- A candle burning in a sealed jar goes out after a short time. Why?
The oxygen is used up
提示Burning needs a gas from the air as well as the fuel.
为什么The wax is still there, but the oxygen in the jar has been used up, so the burning stops.
- Magnesium ribbon burns with a bright white light and leaves a white powder. Name the powder (two words).
Magnesium oxide
提示The metal combines with oxygen from the air.
为什么Magnesium + oxygen → magnesium oxide. The mass of the white powder is more than the mass of the ribbon, because oxygen has joined it.
- Is energy taken in or given out when a fuel burns?
Given out, as heat and light
提示Think how a campfire feels.
为什么Burning is a chemical reaction that releases stored energy. The fuel is the store of energy.
- Write a word equation for magnesium burning in oxygen.
magnesium + oxygen → magnesium oxide
提示Reactants go on the left, the product on the right.
为什么The arrow means 'react to make'. The word oxide shows oxygen has joined the metal.
- In the word equation zinc + sulfur → zinc sulfide, which substance is the product?
Zinc sulfide
提示The product is on the right of the arrow.
为什么Reactants are on the left of the arrow and the products are on the right. Zinc and sulfur are used up to make zinc sulfide.
- Say this word equation as a plain-English sentence: hydrogen + oxygen → water.
Hydrogen reacts with oxygen to make water
提示Read the plus as 'joins up' and the arrow as 'turns into'.
为什么A word equation is a sentence in shorthand: it says what goes in and what comes out.
1★ KS3-CHEM-REA-0035
2★ KS3-CHEM-REA-0036
3★ KS3-CHEM-REA-0037
4★ KS3-CHEM-REA-0038
5★ KS3-CHEM-REA-0039
6★ KS3-CHEM-REA-0040
7★ KS3-CHEM-REA-0041
8★ KS3-CHEM-REA-0042
9★ KS3-CHEM-REA-0043
10★ KS3-CHEM-REA-0044