Chemical Properties and Changes

1. Chemical Properties and Changes

2. Property = a characteristic that gives a substance identity Properties of Vinegar: - clear liquid - density is 1.08 g/mL -strong odor - reacts with baking soda - acidic

3. Composition = the ingredients or make-up of a substance, often represented by a chemical formula Water is composed of Hydrogen and Oxygen Emeralds are composed of Al, Be, Si and O Diamonds are composed of Carbon only

4. Chemical Property Physical Property • can be observed without changing composition • “depends on the matter itself” • Only can be observed when composition changes. • “depends on its reaction with other matter” Methanol / Water

5. Important Physical Properties: • Color • Opacity • Density • Magnetism • Conductivity • (ability to conduct heat or electricity) • Solubility • (ability to form a solution in water or other solvent) • Crystal Form • (grain size, geometric shape of crystal)

6. There is only one chemical property: REACTIVITY …whether something will react with (have a chemical reaction with) another substance.

7. What is a Chemical Reaction? Chemical Reaction: …a rearrangement of the atoms in a substance to produce new substances

8. All chemical reactions can be written as: chemical equations: for example: Methanol + Oxygen  Carbon Dioxide + Water PRODUCTS REACTANTS or: CH3OH + O2 CO2 + 2H2O REACTANTS PRODUCTS

9. So, REACTIVITY is a chemical property …that describes whether something will have a chemical reaction (chemical change) with another substance.

10. Examples of Reactivity: • Reaction with…____ • Flammability • (reaction with O2) • pH • (reaction with water…whether something is an ‘acid’ or a ‘base’) Solder / Mg

11. pH: An important chemical property. pH = a measure of how acidic or basic a substance is. • Turn litmus paper red • React with bases to form salts • Taste Sour ACIDS BASES • Turn litmus paper blue • React with acids to form salts • Taste Bitter

12. = a measure of how acidic or basic a substance is ACIDS BASES pH

13. Which are Physical Properties?Which are Chemical Properties? Physical Physical Chemical Physical Physical Chemical Chemical Physical Chemical Physical • Hardness…………………… • Color………………………. • Reactivity with HCl………. • Magnetism………………... • Density……………………. • pH…………………………. • Flammability……………… • Boiling Point……………… • Corrosiveness……………… • Melting Point………………

14. Chemical Change Physical Change • No new substances are formed. • No change in chemical formula • = “chemical reaction” • New substances are formed. • Chemical Formulae are new or changed, Examples; - Crushing into Powder - All Phase Changes • Examples; • Wood Burning (Combustion) • Iron Rusting (Oxidation)

15. Q: How can we tell if a chemical change has occurred? A: Look for evidence… 5 Signs of a Chemical Reaction: • Formation of a gas • Formation of a solid • Unpredictable Color Change • Radiant Energy (Light) • Thermal Energy (Heat)

16. Ice Melting:Chemical or Physical Change? • Composition does not change; it is still water (H2O). No new substances are formed, so no chemical change. PHASE CHANGE = PHYSICAL CHANGE

17. Phase Changes and Kinetic Theory

18. When a candle melts, some of the wax turns to a liquid and runs down the side. Is this a chemical change or a physical change? Why? • Does the candle become a new substance? • It was wax; it is still wax; liquid wax is still wax Physical Change

19. Enough! Is lighting a match a chemical change or a physical change? Why? • Is a new substance produced? • Does a color change occur? • Is heat and light given off? • Is a gas produced? Chemical Change