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4 Properties of Matter
A burning log undergoes a chemical change resulting in
the release of energy in the form of heat and light
Foundations of College Chemistry, 14th Ed.
Morris Hein and Susan Arena
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Chapter Outline
4.1
Properties of Substances
4.2
Physical and Chemical Changes
4.3
Learning to Solve Problems
4.4
Energy
4.5
Heat: Quantitative Measurement
A. Energy in Chemical Changes
B. Conservation of Energy
4.6
Energy in the Real World
© 2014 John Wiley & Sons, Inc. All rights reserved.
Properties of Substances
Each substance has a set of properties that are
characteristic and give it a unique identity.
Properties are classified as either physical or chemical.
Physical properties are inherent characteristics that can
be determined without altering the composition.
Examples include:
color
taste
odor
state of matter
density
melting point
boiling point
© 2014 John Wiley & Sons, Inc. All rights reserved.
Properties of Substances
Chemical properties describe the ability of a substance
to either undergo a reaction with another substance
or to decompose.
Consider chlorine (Cl2).
Physical Properties: 4 times heavier than air, a gas at
room temperature, greenish-yellow in color, bad odor.
Chemical Change:
2 Na (s) + Cl2 (g)
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2 NaCl (s)
Properties of Substances
No two substances have identical
physical and chemical properties!
© 2014 John Wiley & Sons, Inc. All rights reserved.
Physical and Chemical Changes
Physical changes are changes in physical properties
(such as size and density) or changes in states of matter
without a change in composition.
No new substances are formed during a physical change!
Sawing wood is a physical change – the wood changes
shape, but the resulting pieces are still wood!
© 2014 John Wiley & Sons, Inc. All rights reserved.
Physical and Chemical Changes
In a chemical change, new substances are formed
that have different properties and composition
from the original material.
When copper metal (Cu) is heated in air, the shiny metal
turns black as copper(II) oxide is formed on the surface.
2 Cu (s) + O2 (g)
D
2 CuO (s)
D represents heat
© 2014 John Wiley & Sons, Inc. All rights reserved.
Common Physical and Chemical Changes
Be able to distinguish between a physical
and chemical change.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Let’s Practice!
a.
b.
c.
d.
e.
Which of the following is a physical change?
grinding a rock into powder
hydrogen and oxygen reacting to form water
a shovel rusting
an acid and base reacting to form water
burning sugar
Which of the following is a chemical change?
a.
b.
c.
d.
e.
melting aspirin
breaking a plate
boiling antifreeze
putting sugar in tea
lighting a match
© 2014 John Wiley & Sons, Inc. All rights reserved.
Chemical Equations
A chemical equation is used to represent chemical change.
For example, water decomposes into its elements
when electrolyzed.
2 H2O (l)
2 H2 (g) + O2 (g)
Understanding a chemical equation:
reactants
the starting substances (in this case 2 H2O)
products
the substances formed (in this case 2 H2 + O2)
means “produces”; points towards products
A physical change usually accompanies a chemical change.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Learning to Solve Problems
To succeed in chemistry, you must learn to solve
complicated problems.
READ
Read the problem carefully and determine
what is known and desired. Use units!
PLAN
Determine the unit relationships needed to
solve the problem. Set up the problem so
that the units cancel correctly.
CALCULATE Do the math. Make sure the answer contains
the proper units and significant figures.
CHECK
Check the answer — is it reasonable?
© 2014 John Wiley & Sons, Inc. All rights reserved.
Energy
Energy is the capacity of matter to do work.
There are many types of energy including mechanical,
chemical, electrical and nuclear energy.
Potential energy (PE) is stored energy, the energy
an object possesses due to its position.
A ball located 20 feet above the ground has more PE
than when it is located 10 feet above the ground.
A diver poised on a diving board has a large amount of PE.
When the diver leaves the board, the energy is converted.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Energy
Kinetic energy (KE) is energy that matter possesses
due to its motion.
When water held by a dam is released, its PE converts to
KE which can be used to produce electricity.
Energy can be converted from one form to another.
In chemistry, energy is most frequently released as heat.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Heat: Quantitative Measurement
The SI unit for energy is the joule (J).
The energy required to change the temperature of 1 g
of water by 1 °C is 4.184 J.
4.184 J = 1 calorie
Nutritional calories are actually kilocalories (kcal) and
are represented with a capital C.
Heat and temperature are different concepts.
Imagine two beakers containing water.
In each, the temperature is raised by 30 °C.
The beaker containing twice the water requires twice
the heat to reach the same temperature.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Let’s Practice!
Methane (CH4) is the major compound in natural gas.
Using the reaction below, determine the amount of
energy produced during combustion (in calories).
CH4 (g) + 2 O2 (g)
Knowns
CO2 (g) + 2 H2O (g) + 802.5 kJ
4.184 J = 1 cal
1000 J = 1 kJ
Solving for calories
Calculate
1000 J x 1 cal
x
= 1.918 x 105 cal
802.5 kJ
4.184 J
1 kJ
© 2014 John Wiley & Sons, Inc. All rights reserved.
Heat: Quantitative Measurement
Every substance has a characteristic heat capacity.
The specific heat of a substance is the amount of heat
(gained or lost) required to change the temperature
of 1 g of the material by 1 °C.
The specific heat of water is much higher
than most substances.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Specific Heat Capacity
When an object is heated or cooled, the amount of energy
transferred depends on three things:
1. The amount of material
2. The magnitude of the temperature change
3. The identity of the material gaining or losing energy
The following equation can be used to calculate heat:
q = mCDT
q is heat
m is mass
C is specific heat capacity
DT is change in temperature
© 2014 John Wiley & Sons, Inc. All rights reserved.
Specific Heat Capacity
How much heat is needed to raise the temperature
of 200. g of water by 10.0 °C?
q = mCDT
Knowns
m = 200. g
C = 4.184 J/g°C
DT = 10.0 °C
Solving For q
q = mCDT
Calculate q = (200. g)(4.184 J/g°C)(10.0 °C) = 8.37 x 103 J
© 2014 John Wiley & Sons, Inc. All rights reserved.
Specific Heat Capacity
Calculate the specific heat (J/g°C) of an unknown if
1638 J raises the temperature of 125 g
from 25.0 °C to 52.6 °C.
q = mCDT
Knowns
q = 1638 J
m = 125 g
DT = 52.6 °C – 25.0 °C = 27.6 °C
q
Solving For C C =
mDT
Calculate C =
1638 J
= 0.475 J/g°C
(125 g)(27.6 °C)
© 2014 John Wiley & Sons, Inc. All rights reserved.
Energy in Chemical Changes
All chemical reactions either absorb or release energy.
Chemical changes can produce different kinds of energy,
like electrical energy in a lead storage battery or
heat and light when fuel undergoes combustion.
Chemical changes can also use energy,
such as the electricity used to decompose water or
the solar energy used by plants during photosynthesis.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Conservation of Energy
Energy can be changed from one form to another
or from one substance to another.
The Law of Conservation of Energy states that energy
can be neither created nor destroyed.
When water decomposes, energy is absorbed by the
system so H2 and O2 have higher potential energy.
When hydrogen (H2) is used as a fuel, energy is released
and water (the product) has lower potential energy.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Energy in the Real World
Energy comes from many sources, including petroleum,
coal and woody plants, all derived from the sun.
We use petroleum deposits in the forms of
gasoline and natural gas.
Petroleum is composed of hydrocarbons, compounds
containing only carbon and hydrogen in differing ratios.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Energy in the Real World
Natural gas consists mainly of methane (CH4) with
small amounts of ethane, propane and butane mixed in.
Coal is formed from plant remains stored under high
pressure for many years. The higher the carbon content,
the more energy available in the coal.
© 2014 John Wiley & Sons, Inc. All rights reserved.
The Energy Crisis
To keep up with increasing energy demands,
new renewable energy sources are necessary.
Potential resources include solar, nuclear, biomass,
wind and synthetic fuels.
solar
wind
biomass
© 2014 John Wiley & Sons, Inc. All rights reserved.