Yr7 C3.1 Chemical reactions

What happens to atoms during a chemical reaction?

• They disappear and new atoms appear.

• They rearrange to form new substances.

• They stay in the same arrangement but change size.

Which of the following is NOT a sign of a chemical reaction?

• Change in temperature

• Formation of a gas

• Change in shape

Which of these is an example of a useful product made by chemical reactions?

• Paracetamol

• Wood

• Water

Why are most chemical reactions NOT easily reversible?

• The new substances are too stable.

• The atoms rearrange to form new substances that are difficult to separate.

• Energy is transferred away, preventing reversal.

Which of these statements about catalysts is true?

• A catalyst speeds up a reaction without being used up.

• A catalyst is always required for a reaction to happen.

• A catalyst makes a reaction colder.

Which of these is a chemical reaction?

• Boiling water to make steam

• Dissolving sugar in water

• Baking a cake

What is an example of an unwanted chemical reaction?

• Rusting of iron

• Boiling water

• Melting chocolate

Why do chemical reactions transfer energy?

• Because atoms lose mass during the reaction.

• Because new bonds are made and broken, releasing or absorbing energy.

• Because the number of atoms changes.

Which of these changes is a physical change?

• Burning petrol

• Melting chocolate

• Cooking an egg

Which of the following is a correct statement about chemical reactions?

• They always make new substances.

• They never involve energy transfers.

• They can be easily reversed.