CHEMISTRY: ATOMS, ELEMENTS, AND COMPOUNDS
Physical & Chemical Changes
Combustion
Corrosion
Changes in MatterPhysical Changes No new substance is formed New properties are temporary Change can be reversed There is only a change in form or shape examples
Ice melting Water freezing Chopping wood Tearing paper
Changes of State: a physical change
Changes in Matter
Chemical Changes New substance is formed New properties Cannot reverse the change Examples:
Wood burning (combustion) Iron rusting (corrosion) Baking soda reacting with
vinegar to produce bubbles
Chemical Changes
Evidence of a chemical change: Colour change Heat is absorbed or released Gas bubbles form in a liquid A new solid (precipitate) forms Light is released A new odour is produced A sound is produced
Homework
Read pg. 28 – 30 Answer # 1 – 4 on pg. 30
Corrosion: a chemical change
a metal loses its properties because of a chemical change with its environment
it is a very slow process corrosion looks different for different types of
metals
Corrosion of Iron: Rusting
iron reacts with oxygen to form iron oxide (rust)
the oxygen can come from air or water
Preventing Corrosion
prevention is based on stopping the metal from being exposed to oxygen
avoid exposure to air or water1. paint the surface of the metal
2. spray the bottom and inner surfaces with oil
3. coat with other metals
Homework
Read pg. 34 – 35 Answer # 1 – 3, 5 – 7 on pg. 35
Combustion: a chemical change
Combustion: a chemical change
Homework
Read pg. 38 – 39 Answer # 1 – 5, 7 on pg. 39