Chemical and Physical Changes Notes
Chemical Reactions
Scientists classify matter according to the following diagram:
There are two types of change:
PHYSICAL CHANGES
In a physical change there is only a change of state. The new substance has the same properties as the old one. No new substance(s) are produced.
Eg.ICE WATER STEAM (They are all water!)
For example: ice melting to water or water boiling.
In all of these changes, you can get the original materials back!
A physical change may also involve changing the shape of the substance. For example paper cut into pieces is still paper, cutting wood into pieces is still wood, and moulding a sculpture is still cement or marble!
Physical Properties
Physical properties include: appearance, texture, color, odour, melting point, boiling point, density, solubility, malleability (hammered into thin sheets), ductility (pulled into thin wires), tensile strength (resistance to tension), viscosity ( resistance to flow), compressibility, density – mass per unit of volume)
CHEMICAL CHANGES
In a chemical change one or more NEW substances are created. The new substance is different from the original - has properties that are different than those of the starting materials.
Original materials cannot be obtained back easily. (lighting a match)
Examples of chemical reactions:
-raw egg becomes cooked egg
-cake mix becomes cake
-paper becomes ash
-steel becomes rust
How do we know a chemical change occurred?
If two of the following are produced, a chemical reaction has probably occurred:
-change in temperature
-a new colour appears
-starting colour disappears
-a material with new properties forms
-solids are formed in a liquid
Testing for chemical substances
For oxygen gas – a glowing splint bursts into flame
Hydrogen gas – a flaming splint at the mouth of the tube causes a “pop”
Carbon dioxide gas – limewater solution turns milky
Water vapour – cobalt chloride paper changes from blue to pink