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Properties of Substances
Properties of Substances
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• A property is a characteristic of a substance.
• Each substance has a set of properties that are characteristic of that substance and give it a unique identity.
Properties of a Substance
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Physical PropertiesPhysical Properties
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• The inherent characteristics of a substance that are determined without changing its composition.
• Examples: tastecolorphysical statemelting pointboiling point
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• 2.4 times heavier than air
• color is yellowish-green
• odor is disagreeable
• melting point –101oC
• boiling point –34.6oC
Physical Properties of Chlorine
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Chemical PropertiesChemical Properties
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Describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition.
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• It will not burn in oxygen.
• It will support the combustion of certain other substances.
• It can be used as a bleaching agent.
• It can be used as a water disinfectant.
• It can combine with sodium to form sodium chloride.
Chemical Properties of Chlorine
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Physical ChangesPhysical Changes
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• Changes in physical properties (such as size shape and density) or changes in the state of matter without an accompanying change in composition.
• Examples:
Physical Changes
tearing of paperchange of ice into waterchange of water into steamheating platinum wire
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Chemical ChangesChemical Changes
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In a chemical change new substances are formed that have different properties and composition from the original material.
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Formation of Copper(II) Oxide
Heating a copper wire in a Bunsen burner causes the copper to lose its original appearance and become a black material.
The black material is a new substance called copper(II) oxide. Copper is 100% copper by mass. Copper (II) oxide is: 79.94% copper by mass 20.1% oxygen by mass.
The formation of copper(II) oxide from copper and oxygen is a chemical change. The copper (II) oxide is a new substance with properties that are different from copper.
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Formation of Copper(II) Oxide
Copper(II) oxide is made up of Cu2+
and O2- Neither Cu nor O2 contains Cu2+ or O2-A chemical change has occurred.
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Chemical EquationsChemical Equations
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Chemical symbols can be used to express chemical reactions
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Copper plus oxygen yields copper(II) oxide.
yield productreactants
heat
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Conservation of Mass
Conservation of Mass
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No change is observed in the total mass of the substances involved in a chemical change.
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sodium + sulfur sodium sulfide
46.0 g 32.1 g 78.1 g
78.1 g product
mass productsmass products
78.1 g reactant →
mass reactantsmass reactants ==
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Heat: Quantitative Measurement
Heat: Quantitative Measurement
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Heat• A form of energy associated
with small particles of matter.
Temperature• A measure of the intensity of heat, or of how hot or cold a system is.
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Units of Heat EnergyUnits of Heat Energy
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• The SI unit for heat energy is the joule (pronounced “jool” rhymes with fool).
• Another unit is the calorie.
4.184 J = 1 cal
(exactly) 4.184 Joules = 1 calorie
This amount of heat energy will raise the temperature of 1 gram of water 1oC.
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Specific HeatSpecific Heat
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The specific heat of a substance is the quantity of heat required to change the temperature of 1 g of that substance by 1oC.
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Specific Heat of SubstancesSubstance Specific heat (cal/gC)Water 1.00
Ethyl alcohol 0.511
Ice 0.492
Steam 0.481
Iron 0.113
Copper 0.0921
Gold 0.0312
Lead 0.0305
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The units of specific heat in calories are:
o
caloriesgram Celcius
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The relation of mass, specific heat, temperature change (Δt), and quantity of heat lost or gained is expressed by the general equation:
Heat (cal) = mass (g) specific heat (cal/g C) Δt (C)
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ExampleExample
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Calculate the specific heat of a solid in cal/goC if 391.5 cal raise the temperature of 125 g of the solid from 25.0oC to 52.6oC.
heat = (mass)(specific heat)Δt
heat = (g)(specific heat)Δtheat
specific heat = g Δ
t
heat = 391.5 cal
mass = 125 g
Δt = 52.6oC – 25.0oC = 27.6oC
specific heat =o
1638 J125 g 27.6 C
391.5 cal 0.113 cal g C
=
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Energy in Chemical Changes
Energy in Chemical Changes
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In all chemical changes, matter either absorbs or releases energy.
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Energy Release From Chemical Sources
Type of Energy
Energy Source
Electrical Storage batteries
Light A lightstick. Fuel combustion.
Heat and Light Combustion of fuels.
BodyChemical changes occurring within body cells.
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Chemical Changes Caused byAbsorption of Energy
Type of Energy
Chemical Change
ElectricalElectroplating of metals. Decomposition of water into hydrogen and oxygen
Light Photosynthesis in green plants.
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