Presentation on theme: "Physical and Chemical Changes 1.7. A burning candle – what happens? As the candle burns, the wax melts (a solid becomes a liquid), and then it hardens."— Presentation transcript:
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. The wax also combusts producing heat and light. This chemical change involves the wax becoming carbon dioxide, water and energy.
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. Most physical changes are easy to reverse.
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. Chemical changes are difficult to reverse.
There are usually clues that a chemical change has happened: A new colour appears. Heat or light is given off. Bubbles of gas are given off. A solid material (called a precipitate) forms in a liquid. The change is 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)
Read pages 28-30 and on page 30 answer questions 1-4. Copy the questions and the answers into your notebook.
Page 30 questions 1-4 1. Explain how a physical change differs from a chemical change. Chemical changes involve production of a new substance with new properties. No new substances are produced in physical changes.
2. a) Garbage rotting chemical b) Cutting up carrots physical c) A silver spoon turning black chemical d) Making tea from tea leaves physical e) Bleaching a stain chemical f) Boiling an egg chemical
Question 3 Changes occur more quickly at high temperatures. Putting candles together tends to concentrate heat more and the candles will be at a higher temperature. For emergencies, non-dripping and non- smoking candles should be kept on hand. (or battery operated)
Question 4 Evaporation, mixing, and condensation are physical changes. Combustion, catalytic conversion and rusting are chemical changes.