1. 3.3 Physical and Chemical Changes
(c) McGraw Hill Ryerson 2007

2. (c) McGraw Hill Ryerson 2007
Physical Change: the appearance of a substance changes, but the chemical bonds holding the substance together do NOTchange. Examples: changes in state, dissolving
See page 98
(c) McGraw Hill Ryerson 2007

3. (c) McGraw Hill Ryerson 2007
Chemical Change: new substances are produced in the process of breaking and/or forming chemical bonds
Evidence of chemical change:
Colour change
Heat, light, sound produced or consumed
Bubbles of gas form
Formation of a precipitate
The change is difficult to reverse
Ex) 2Na + Cl2  2NaCl
(c) McGraw Hill Ryerson 2007

4. (c) McGraw Hill Ryerson 2007
Energy Changes
In both phys. & chem. changes, energy changes take place
can mean releasing to or absorbing energy from the environment
Exothermic reactions involve the overall release of energy in the form of heat and light.
Endothermic reactions involve the overall absorption of energy.
Instant Cold Pack: Endothermic
Campfire: exothermic
See page 99
(c) McGraw Hill Ryerson 2007

5. Applications of Chemical Changes
Some chemical changes are positive & some are negative:
Corrosion is major problem for steel structures
First nations people of the Pacific Coast have used smoking as a means of preserving food. Smoke causes chemical changes in meat that kill bacteria.
Take the Section 3.3 Quiz
See page 100
(c) McGraw Hill Ryerson 2007