Introduction to Reactions

Question 1

Signs of a chemical change

Answer 1

• a gas has been given off
• there is a colour change
• there is a different smell
• there is heat given out or absorbed
• the change cannot be easily reversed
• new substance formed. ie chemical bonds are broken and formed
• light produced

Question 2

Signs of a physical change

Answer 2

• the substance changes state
• the change can be easily reversed
• no new substances are formed
• the mass of the object is the same at the end of the change
• no change in the chemical bonds (intermolecular forces can be overcome
• dissolving and melting