Physical and Chemical Changes and Properties

1. Physical and Chemical Changes and Properties

2. Physical Properties • A characteristic that can be observed or measured without changing the object. • Density, color, odor, taste, hardness, melting point, boiling point • Extensive – Depends on the amount of substance present • Volume, mass, etc • Intensive – Does not depend the amount of substance • Density, color, etc

3. More on Extensive Properties • Extensive - Properties that do depend on the amount of matter present. • Mass - A measurement of the amount of matter in a object (grams). • Weight - A measurement of the gravitational force of attraction of the earth acting on an object. • Volume - A measurement of the amount of space a substance occupies. • Length, Width, Height – obvious what this is

4. More on Intensive Properties • Intensive - Properties that do not depend on the amount of the matter present. • Color, Odor • Luster - How shiny a substance is. • Malleability - The ability of a substance to be beaten into thin sheets. • Ductility - The ability of a substance to be drawn into thin wires. • Conductivity - The ability of a substance to allow the flow of energy or electricity. • Hardness - How easily a substance can be scratched. • Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. • Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure). • Density - The mass of a substance divided by its volume

5. Density • Density = Mass (g)/Volume (mL or cm3) • Each substance has a generally unique density, and they can be identified by their density. • More Dense substances sink in less dense substances • Less Dense substances float on more dense substances

6. Density Practice Problem #1 • If a block of copper measures 2.00 cm x 4.00 cm x 5.00 cm and a mass of 356 g, what is its density? • D = m/v • M = 356 g • V = 2.00 cm x 4.00 cm x 5.00 cm = 40.0 cm3 • D = 356 g/40.0 cm3 = 8.90 g/cm3

7. Density Practice Problem #2 • The density of mercury is 13.6 g/mL. What is the mass of 8.20 mL of mercury? • D = m/v • M = D x V • D = 13.6 g/mL • V = 8.20 mL • M = 13.6 g/mL x 8.20 mL = 111.52 g

8. Density Practice Problem 3 • Which of the following will float on water?

9. Other Properties • Volume: The amount of space an object takes up. Measured in mL or cm3. • Viscosity: The resistance to flow. The greater the viscosity, the slower something will move as a result. • Melting point/Freezing point: The point at which a substance changes from a solid to a liquid. • Boiling point/condensation point: The point at which a substance changes from a liquid to a gas.

10. Viscosity Problem • Pancake Syrup and Water were both poured out of a container. Which would pour more slowly and why? • The Pancake Syrup because it is more Viscous.

11. Example Review Problems • Aluminum has a density of 2.70 g/cm3. If a block of aluminum were massed at 20.00 g, then what is the volume? • Three substances were placed in a container, A has a density of 1.789 g/cm3, B has a density of 0.825 g/cm3, and C has a density of 1.000 g/cm3. What order will the substances be in the container?

12. More Examples of Density • Gasoline floats on water, explain why.

13. Chemical Properties • The ability of a substance to combine with or change into one or more substances • How something reacts with something else • 5 signs something has reacted: • Gas released • Energy released (Heat or Light) • Change in Odor • Change in Color • Solid (Precipitant) formed • Aqueous means the substance is dissolved in water.

14. Law of Conservation of mass • Mass cannot be created or destroyed in a chemical reaction, just rearranged. • The starting mass in a chemical reaction must equal the ending mass.

15. Terms of chemical reactions • Reactant: What you start with • Product: What you end up with • 2 H2 + O2 2 H2O • Reactants Products • The arrow always points to the Products

16. States of Matter • Solid – Definite Shape and volume • Liquid – Definite volume, Indefinite Shape • Gas – Indefinite Shape and Volume

17. Physical Changes • Changes in a substance that doesn’t change the chemical composition of the substance • State of Matter Change • Cutting • Breaking • Bending • Crushing • Aqueous means the substance is dissolved in water. Dissolving something in water is a physical change.

18. PHYSICAL CHANGE • A Substance becomes a different state of matter • The Original Chemical Formula Remains • Liquid Water Freezes to produce Ice • Water is still Water • Liquid Water Boils to Produce Steam • Water is still Water

19. WORDS HAVE MEANING • PHYSICAL Words • Melts • Boils • Breaks • Shatters • Cut • Freezes • Sublimates

20. Chemical Changes • Changing a substance into a completely new substance 5 signs something has reacted: Gas released Energy released (Heat or Light) Change in Odor Change in Color Solid (Precipitant) formed

21. CHEMICAL CHANGES • One or more substances change to produce One or more NEW Substances • Ammonia reacts with Water to Produce Ammonium Hydroxide • Silver Nitrate reacts with Zinc to produce Silver and Zinc Nitrate • Compounds get rearranged to produce new compounds

22. CHEMICAL WORDS • Reacts • Burns • Combusts • Replaces • Produces • Decomposes • Releases • Rusts

23. Other Important Concepts • Element: The smallest substance that can be broken down chemically. They are on the periodic table. • Compound: Two or more different substances chemically combined • Homogenous Mixture: Two or more different substances physically combined, it looks the same throughout • Heterogeneous Mixture: Two or more different substances physically combined, has visually seeable parts.

24. Alloys • A homogenous mixture of two or more metals. • Examples: (Bronze, Brass, Nickel Steel) • This is a Physical combination and a physical change.