Physical and chemical changes, endothermic and exothermic reactions

Question 1

What is a physical change?

Answer 1

A physical change is a change in the physical property of a substance that is reversible, and where no bonds between atoms are broken, and no new substances are made.

eg. Melting, condensation, boiling, dissolving

Question 2

What is a chemical change?

Answer 2

A change occurs when the bonds between atoms are broken, and atoms are rearrange to create new substances, usually irreversible.

eg. lighting a match, baking a cake, explosion, consuming food.

Question 3

What are signs of a chemical reaction?

Answer 3

• Energy in the form of heat is either absorbed or produced
• Permanent colour change occurring (non-reversible)
• When a precipitate (powder) forms
• Gas produced- we can identify this if there are bubbles that have been formed or if a new/ unusual smell is observed from the reaction
• Energy in the form of light is produced eg. lighting a match

Question 4

What is an exothermic reaction?

Answer 4

An exothermic reaction is one where more heat energy is being released when new bonds are formed, than is absorbed/taken in to break bonds.

This cause the temperature of the surroundings to increase (feel hot).

Question 5

What is an endothermic reaction?

Answer 5

An endothermic reaction is one where more energy is being absorbed/taken in to break bonds than is released when new bonds are made.

This causes the temperature of the surrounding s to decrease (feel cold)