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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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