Kinetic Particle Theory

Physical Change
- NO new substance formed.
- Usually easily reversible.
- May or may not involve heating
- Some types of physical changes include

1.     Grinding, tearing cutting or shaping

2.  A change of state or phase from a solid to liquid.

Chemical Change
-  New chemical substance(s) is/are formed
- Usually irreversible (Some chemical change can be reversed under special conditions)
- Heat energy may be given off or absorbed
- Light energy may be given off or absorbed

Signs of a chemical change

- A change in colour

- Production of a gas

- Formation of a precipitate from mixing solutions

- Change of temperature

All of the above must follow the formation of a new chemical substance

Chemical reactions

- A process in which new chemical substances are formed

Eg.    A+B   ->   C+D

    Reactants -> Products

- New chemical substances formed due to rearrangement of atoms

- No atoms are created or destroyed, according to le Law of Constant Mass

Types of chemical reactions:

B     Combination (Synthesis)

~ Two or more substances combine to form a new substance

~ Eg. Magnesium + oxygen -> magnesium oxide

B     Decomposition

~ A substance breaks down into two or more simpler substances

B     Combustion or burning

~ Combination of a substance with oxygen

~ Heat and light energy are given off

~ Eg. Hydrocarbon + oxygen -> carbon dioxide + water

B     Displacement reaction

~ A chemical reaction with an atom/ a group of atoms that got replaced by another atom/group of atoms

~ Eg. Hydrogen bromide -> hydrogen chloride + bromine