Physical and Chemical Change

Question 1

Physical change?

Answer 1

Physical change occurs when no new substances are formed.
Energy changes are small in relation to chemical changes.
The mass, number of atoms and molecules are conserved.

Question 2

Chemical change?

Answer 2

Chemical change occurs when new chemical substances are formed.
Energy changes are larger in relation to physical changes.
The mass and number of atoms are conserved but number of molecules is not conserved.

Question 3

Synthesis reactions?

Answer 3

When 2 or more substances (simpler substances) combine chemically to form more complex compounds eg. Iron and sulfur combine to make iron sulfide.

Question 4

Decomposition reactions?

Answer 4

When a complex compound breaks down to form simpler substances eg. Potassiom chlorate breaks down to form potassium chloride and oxygen.

Question 5

Exothermic reactions?

Answer 5

When more energy is released in a reaction than it takes in eg. A reaction of hydrogen with oxygen

Question 6

Endothermic reactions?

Answer 6

When more energy is absorbed in a reaction than it releases eg. Copper carbonate is broken down into copper oxide and carbon dioxide when it is heated. During the reaction thermal energy is absorbed and is stored as chemical potential energy in the products

Question 7

The law of conservation of energy?

Answer 7

And an isolated system, energy cannot be created or destroyed; it can only be transferred from one place to another

Question 8

The law of constant proportions?

Answer 8

Elements combined in fixed ratios with one another in chemical compounds.