Physical and Chemical Changes and Properties

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

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

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

Density Density = Mass (g)/Volume (mL or cm 3 ) 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

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 cm 3 D = 356 g/40.0 cm 3 = 8.90 g/cm 3

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 = g

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

Other Properties Volume: The amount of space an object takes up. Measured in mL or cm 3. 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.

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.

Example Review Problems Aluminum has a density of 2.70 g/cm 3. If a block of aluminum were massed at g, then what is the volume? Three substances were placed in a container, A has a density of g/cm 3, B has a density of g/cm 3, and C has a density of g/cm 3. What order will the substances be in the container?

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

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.

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.

Terms of chemical reactions Reactant: What you start with Product: What you end up with 2 H 2 + O 2  2 H 2 O ReactantsProducts The arrow always points to the Products

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

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.

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

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

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

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

CHEMICAL WORDS Reacts Burns Combusts Replaces Produces Decomposes Releases Rusts

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.

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