Physical and Chemical Changes Chapter 1.7

Physical and Chemical Changes (Not the same as Phys. and Chem. Properties) Physical Change: The substance involved remains the same, even though it may change state or form. Ex. Pour melted chocolate on ice cream. It still tastes the same because the particles have not changed, it just hardened (changed state) because the ice cream was cool.

Video Physical Changes Video Physical Changes

Chemical Changes: The original substance is changed into one or more different substances that have different properties. Examples: Burning, Cooking, Rusting… Burning, Cooking, Rusting… The formation of water from hydrogen and oxygen. The formation of rust from iron and oxygen.

Video Chemical Changes Video Chemical Changes

There are usually clues that a chemical change has happened: A new colour appears. A new colour appears. Heat or light is given off. Heat or light is given off. Bubbles of gas are given off. Bubbles of gas are given off. A solid material (called a precipitate) forms in a liquid. A solid material (called a precipitate) forms in a liquid. The change is difficult to reverse. The change is difficult to reverse.

A Burning Candle – What happens? As the candle burns, the wax melts (a solid becomes a liquid), and then it hardens (a liquid becomes a solid). These are physical changes. As the candle burns, the wax melts (a solid becomes a liquid), and then it hardens (a liquid becomes a solid). These are physical changes. When candle wax melts, it is still wax. When candle wax melts, it is still wax. Most physical changes are easy to reverse. Most physical changes are easy to reverse.

A Burning Candle – What happens? The wax also combusts producing heat and light. This chemical change involves the wax becoming carbon dioxide, water and energy. The wax also combusts producing heat and light. This chemical change involves the wax becoming carbon dioxide, water and energy. As the wax melts, some of the wax particles combine with oxygen to produce water vapour, carbon dioxide, heat and light, it is still wax. As the wax melts, some of the wax particles combine with oxygen to produce water vapour, carbon dioxide, heat and light, it is still wax. Most chemical changes are difficult to reverse. Most chemical changes are difficult to reverse.

Sample Chemical Changes (Always involve the production of a new substance.) Ex. 1: H + O  H 2 O (water) gas gasliquid gas gasliquid Reactants: Left side Products: Right side Reactants: Left side Products: Right side Ex. 2: C + 2O  CO 2 (carbon dioxide) C + 2O  CO 2 (carbon dioxide) Ex. 3: 6C + 12H + 6O  C 6 H 12 O 6 (sugar) Ex. 4: 3C + 8H  C 3 H 8 (Propane)

HOMEWORK Read pages and on page 30 answer questions 1-4. Copy the questions and the answers into your notebook.