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Properties of MatterChapter 4

Hein and Arena

Eugene Passer

Chemistry Department

Bronx Community College

© John Wiley and Sons, Inc

Version 1.0

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Properties of

Substances

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• A property is a characteristic of a

substance.

• A substance has both physical and

chemical properties.

Properties of a Substance

Recall that a substance is a particular kind of matter. It has a

fixed composition and distinct properties.

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Physical Properties

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• Physical properties are inherent

characteristics of a substance that are

determined without changing its

composition.

taste

color

physical state

melting point

boiling point

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Chemical Properties

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Chemical properties describe the ability

of a substance to form new substances,

either by reaction with other substances

or by decomposition.

• Will it burn in oxygen.

• Will it support the combustion ofcertain other substances.

• Can it be used as a disinfectant.

• Can it combine with sodium toform sodium chloride, NaCl.

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Physical Changes

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tearing of paper

change of ice into water

change of water into steam

heating platinum wire

• Changes in physical properties (such as

size, shape and density) or changes in the

state of matter without an accompanying

chemical change are physical changes.

• Examples:

Physical Changes

Note that no new substance(s) are formed.

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Chemical 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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Heating a copper wire in a Bunsen burner

causes the copper to lose its original appearance

and become a black material.

Formation of Copper(II) Oxide

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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Chemical Equations

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The Information present in a

“Balanced” Chemical Equation

• Species present as reactants and

products (i.e. atoms, ions, molecules,

etc.)

• Amounts present (i.e. moles)

• Stoichiometry (i.e. mole ratios)

• Direction of reaction (i.e. favored)

• Reaction conditions (i.e. heat)

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Water decomposes into hydrogen and

oxygen when electrolyzed.

reactant productsyields

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Chemical symbols can be used to

express chemical reactions

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Water decomposes into hydrogen and

oxygen when electrolyzed.

reactant yields

2H2O 2H2 O2

products

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Copper plus oxygen yields copper(II)

oxide.

yield productreactants

heat

2Cu O2 2CuO

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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 of products

78.1 g reactant →

mass of reactants =

This is the Law of Conservation of Mass:

In a chemical reaction, mass is neither

created nor destroyed.

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Heat Energy and the Specific Heat of a Substance

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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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The units of

specific heat in

joules are:o

Joules

gram Celcius

o

J

g C

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The units of

specific heat in

calories are:o

calories

gram Celcius

o

cal

g C

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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:

q = mcDt

heat = specific

heatmass

temperature

change

(tf - to)

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Heat

q = mcDTWhere:m = mass (in g)

C = Specific Heat Capacity (in J/g°C)

DT = Tf - To (in °C)

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Question

How much heat (q) is required to raise

the temperature of 1.00 g of water from

25°C to 75°C?

The specific heat of water is 4.184 J/g°C.

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Answer

m = 1.00 g

c = 4.184 J/g°C

DT = (Tf – Ti) = 75 – 25 = 50.°C

q = mcDT = (1.00 g)(4.184 J/g°C)(50.°C)

q = 210 J

How much heat (q) is required to raise the

temperature of 1.00 g of water from 25.0°C to

100.°C? The specific heat of water is 4.184 J/g°C.

1 2 3 4

17%

71%

4%8%

A “Clicker” Question

t, w1 &w2

1. 418 J

2. 401 J

3. 613 J

4. 310 J

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Answer

m = 1.00 g

c = 4.184 J/g°C

DT = (Tf – Ti) = 100. – 25.0 = 75.°C

q = mcDT = (1.00 g)(4.184 J/g°C)(75.°C)

q = 310 J

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13.5

Heating curve for a pure substance.

q = mcDT

Heat flow that produces a temperature

change w/o a phase change (i.e. A-B,C-D

and E-F).

q = mc

Heat flow that

produces a phase

change w/o a

temperature

change (i.e. B-C

and D-E).

melting

freezing

evaporation

condensation

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Latent Heat

… is the heat energy involved in a phase changewith no accompanying change in temperature.

q = mcWhere:

m = mass (g)C = Heat of Fusion (J/g)

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The heat of fusion of ice at 0oC is 335 J/g.

q = mc

How many joules of energy are needed to change 10.0

g of ice at 0.00oC to water 20.0oC?

Determine the joules necessary to melt 10.0 g of ice.

33.35 x 10 J 10.0 g335 J

=1 g

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How many joules of energy are needed to change 10.0

g of ice at 0.00oC to water 20.0oC?

Next, determine the joules necessary to heat 10.0 g

of water from 0.00oC to 20.0oC; q = mcDT.

The total heat absorbed by the system is the heat

required to melt the ice plus the heat required to raise

the water temperature from 0.00oC to 20oC.

q = 3350 J + 837 J = 4.19 x 103 J

The specific heat of water is 4.184 J/goC.

837 J 10.0 g o

4.184 J

1 g C

o20.0 C =

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Energy in

Chemical Changes

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In all chemical reactions, matter either absorbs

energy( referred to as Endothermic reactions)

or releases energy( referred to as Exothermic

reactions).

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Examples of Heat Energy in Chemical

Reactions

Endothermic Reaction:

N2 + O2 + Heat 2NO

(heat is a reactant)

Exothermic Reaction:

CH4 + 2O2 2H2O + CO2 + Heat

(heat is a product)

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Conservation of

Energy

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Law of Conservation of Energy

Energy can be neither created nor destroyed,

though it can be transformed from one form

of energy to another form of energy (e.g. heat

to potential energy or visa versa).

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An energy transformation occurs

whenever a chemical change occurs.

• If energy is absorbed during a chemicalchange, the products will have morepotential energy than the reactants. This isan endothermic reaction.

• If energy is released in a chemical

change, the products will have less

potential energy than the reactants. This is

an exothermic reaction.

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4.4

H2 + O2 have higher

potential energy than H2O

energy is given offenergy is absorbed

Electrolysis of Water Burning of

Hydrogen in Air

higher potential energy lower potential energy

Endothermic Reaction Exothermic Reaction

The difference in potential energies between the reactants and the products is

heat (i.e. enthalpy).

CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + 802.5 KJ

Is this reaction Exothermic or Endothermic and is

the PE of the products higher or lower than the PE

of the reactants?

1 2 3 4

20%

30%

4%

46%

A “Clicker” Question

1. Endothermic, Higher

2. Exothermic, Lower

3. Endothermic, Lower

4. Exothermic, Higher

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AnswerCH4(g) + 2O2(g) CO2(g) + 2H2O(g) + 802.5 KJ

Heat is a product, so heat is being released and the

PE of the products will be lower than the PE of the

reactants.

802.5 KJ

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