Presentation on theme: "Chemical Properties & Physical and Chemical Changes."— Presentation transcript:
Chemical Properties & Physical and Chemical Changes
Physical changes are those changes that do not result in the production of a new substance. If you melt a block of ice, you still have H 2 O at the end of the change.
If you break a bottle, you still have glass. Painting your nails will not stop them from being fingernails. Some common examples of physical changes are: melting, freezing, condensing, breaking, crushing, cutting, and bending.
When a change of state occurs, molecules or atoms may move faster or slower, may spread out or clump together, but they do not change. i.e. An H2O molecule is still an H2O molecule!
Some, but not all physical changes can be reversed. You could refreeze the water into ice, but you cannot put your hair back together if you dont like your haircut!
Special types of physical changes where any object changes state, such as when water freezes or evaporates, are sometimes called change of state operations.
Physical change A substance alters its physical form, not its composition Chemical change A substance is converted into a new substance The distinction between physical and chemical change.
Sample Problem 1.5 Calculating Density from Mass and Length PROBLEM: Lithium (Li) is a soft, gray solid that has the lowest density of any metal. If a slab of Li weighs 1.49 x 10 3 mg and has sides that measure 20.9 mm by 11.1 mm by 11.9 mm, what is the density of Li in g/cm 3 ?
CHEMICAL PROPERTIES Chemical properties can ONLY be observed AS the substances are changing into different substances.
Chemical changes, or chemical reactions, are changes that result in the production of a new substance.
FLAMMABILITY: A materials ability to BURN in the presence of OXYGEN A chemical property
REACTIVITY: How readily (easily) a substance combines chemically with other substances. A chemical property
Some Characteristic Properties of Copper Table 1.1 Physical PropertiesChemical Properties reddish brown, metallic luster easily shaped into sheets (malleable) and wires (ductile) good conductor of heat and electricity density = 8.95 g/cm 3 melting point = C boiling point = C slowly forms a basic blue-green sulfate in moist air reacts with nitric acid and sulfuric acid slowly form a deep-blue solution in aqueous ammonia
When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon. When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide.
Common examples of chemical changes that you may be somewhat familiar with are; digestion, respiration, photosynthesis, burning, and decomposition.
Physical or Chemical Change? Painting Wood PHYSICAL
Physical or Chemical Change? Burning Paper CHEMICAL
Physical or Chemical Change? Digestion of food CHEMICAL
Physical or Chemical Change? Sugar dissolving in water PHYSICAL
Physical or Chemical Change? Iron turning red when heated PHYSICAL
Physical or Chemical Change? Evaporation PHYSICAL
Physical or Chemical Change? A pond freezing in winter PHYSICAL
Physical or Chemical Change? Melting ice PHYSICAL
Physical or Chemical Change? Cutting wire PHYSICAL
Physical or Chemical Change? Painting fingernails PHYSICAL
Physical or Chemical Change? Cutting fabric PHYSICAL
Physical or Chemical Change? Baking muffins CHEMICAL
Physical or Chemical Change? Shattering glass PHYSICAL
Physical or Chemical Change? Decomposition of old leaves CHEMICAL
Physical or Chemical Change? Wrinkling a shirt PHYSICAL
Physical or Chemical Change? An old nail rusting CHEMICAL
Common Decimal Prefixes Used with SI Units Table 1.3
Substance Physical State Density (g/cm 3 ) Densities of Some Common Substances * Table 1.5 HydrogenGas OxygenGas Grain alcoholLiquid WaterLiquid Table saltSolid 2.16 AluminumSolid 2.70 LeadSolid11.3 GoldSolid19.3 * At room temperature(20 0 C) and normal atmospheric pressure(1atm).
Physical versus Chemical Properties Unit II - Part 1 The study of matter
Matter: anything that has mass and takes up space Mass – the amount of matter in something Volume – the amount of space something occupies Which of the following is matter? A car? A box? You? Reviewing MATTER
What is a property? Property: a characteristic of a substance that can be observed
Physical Property Physical property: a property that can be observed without changing the identity of the substance. Examples: luster malleability: the ability to be hammered into a thin sheet ductility: the ability to be stretched into a wire melting point boiling point density solubility specific heat
In a physical change no new substances are formed Physical changes include changes of state. liquid to solid: Solidifying or Freezing solid to liquid: Melting liquid to gas: Evaporation or Boiling gas to liquid: Condensation gas to solid or solid to gas: Sublimation
Special Physical Properties Melting point: the temperature at which a substance changes from a solid to a liquid at a given pressure water = 0 o C Boiling point: the temperature at which a substance changes from a liquid to a gas at a given pressure water = 100 o C
Chemical Properties Chemical property: a property that can only be observed by changing the identity of the substance Examples: flammability ability to rust reactivity with vinegar
Density Density is the amount of mass per unit of volume. Density can be used to identify a substance. The density of water is 1.0g/mL
Density Calculations Calculations: D = m/V = g/mL = g/cm 3 Ex: A cube has a mass of 2.8 g and occupies a volume of 3.67 ml. Would this object float or sink in water? Mass = 2.8 gVolume = 3.67 mL D = 2.8g/3.67 mL= 0.76 g/mL This object would float in water because its density is less than water (1.0 g/mL).
More Density Calculations Ex: A liquid has a mass of 25.6 g and a volume of 31.6 mL. Use the table below to identify the substance. M=25.6 gV=31.6 mL D = 25.6 g/31.6 mL D= 0.81 g/mL The substance is ethanol.
Rules for Rounding Off Numbers 1. If the digit removed is more than 5, the preceding number increases by rounds to 5.38 if three significant figures are retained and to 5.4 if two significant figures are retained. 2. If the digit removed is less than 5, the preceding number is unchanged rounds to if three significant figures are retained and to 0.24 if two significant figures are retained. 3.If the digit removed is 5, the preceding number increases by 1 if it is odd and remains unchanged if it is even rounds to 17.8, but rounds to If the 5 is followed only by zeros, rule 3 is followed; if the 5 is followed by nonzeros, rule 1 is followed: rounds to 17.6, but rounds to Be sure to carry two or more additional significant figures through a multistep calculation and round off only the final answer.
Clues that a Chemical Change has occurred. Color change Heat or light given off Odor given off Gas released Solid forming in a liquid