Regents Chemistry
Topic IV
Physical Behavior of
Matter
Different Phases of Matter
• An element, compound or mixture can exist in the
form of a solid, liquid or a gas
• Solid – rigid form, definite volume and shape,
strong attractive forces and crystalline structure
• Liquid – not held together as well, can move past
one another, no definite shape but definite
volume
• Gas – minimal attractive forces, no definite shape
or volume, expand to shape of container
Other Phases
• Vapor – is the gaseous phase of a substance that is a liquid or
a solid at normal conditions: ex: water vapor
• Plasma – is a gas or vapor in which some or all of the
electrons have been removed from the atoms. ex: In a planet’s
core!
Heating and Cooling Curves
• Heating Curves: Constant rate of heating of a
substance over time – endothermic process!
What Can We Learn From a
Heating Curve?
• AB: heating of a solid, one phase
present, kinetic energy increases
• BC: melting of a solid (melting), two
phases present, potential energy
increases, kinetic energy remains
constant
• CD: heating of a liquid, one phase
present, kinetic energy increases
What Can We Learn From a
Heating Curve?
• DE: boiling of a liquid (Vaporization),
two phases present, potential
energy increases, kinetic energy
remains constant
• EF: heating of a gas, one phase
present, kinetic energy increases
***We can tell when the kinetic energy remains constant
because the temperature is not increasing!***
Cooling Curves
• Shows the constant rate of cooling of a gas at high
temperature – an exothermic process
Summary of a Cooling Curve
• AB: cooling of a gas (vapor), one phase
present, kinetic energy decreases
• BC: condensation of the gas (vapor) to
liquid, two phases present, potential
energy decreases, kinetic energy
remains constant
• CD: cooling of a liquid, one phase
present, kinetic energy decreases
Summary of a Cooling Curve
• DE: solidification (freezing) of a liquid,
two phases present, potential
energy decreases, kinetic energy
remains the same
• EF: cooling of a solid, one phase
present, kinetic energy decreases
Substances That Do Not Follow the
Curves
• Some substances change directly from a solid to a gas –
Sublimation
• Example: CO2 changes from a solid to a gas a normal atmospheric
pressure
• Some substances change directly from gas to a solid –
Deposition
Practice Problem
Which portions of the graph represent times when heat is
absorbed and potential energy increases while kinetic
energy remains constant?
worksheet
Regents Chemistry
• Temperature Scales
Temperature Scales
Celsius
 Based
°C
on boiling point/freezing point of water
Kelvin
 Based
K
on absolute zero
Fahrenheit
 Used
°F
in U.S. and Great Britain
Conversions
 Key
Equations
Celsius to Kelvin
K = °C + 273
Fahrenheit to Celsius
°C = 5/9 (°F - 32)
Kelvin to Celsius
°C = K - 273
Celsius to Fahrenheit
°F = 9/5(°C) + 32
**Add the conversions on the right to your worksheet
Practice Problems
 Convert
10 °C to °F
°F = 9/5(°C) + 32 = 9/5 (10 °C) + 32
= 50°F
Convert 25°C to K
K = °C + 273
Worksheet

Add the Fahrenheit and Celsius conversions
to worksheet
 Finish worksheet using p. 36 - 43 from text
 Answer problems on p. 52 #71-76 on
worksheet - write out question and answer

Homework: p.52 #77,78,79 (a-e)
Regents Chemistry
• Measurement of Heat Energy
Energy and Energy Changes
 Energy
is the capacity to do work. In
other words, it allows us to do things!
 Energy surrounds us and is involved in all
of life’s daily functions.
 It comes in many forms!
Energy and Energy Changes
 Energy
can be used to change the
temperature of a substance
 As
we heat a substance (put in heat), the
vibration of molecules in a substance
increases.
 Example:
When a solid is heated, the
molecules vibrate until they break free and the
substance melts.
Specific Heat Capacity
• The specific heat capacity of a substance is the amount of heat
required to raise 1 gram of the substance by 1 degree Celsius
• For water it is 4.184 J / g• K
• Compared to other substances, water has a very high specific
heat..what does this mean?
Specific Heat Capacities
• Check out the specific heat capacities of different substances!
Measurement of Heat Energy
• Question: You pool absorbs how many much heat energy
when it warms from 20 °C to 30 °C?
• It easy is we use a formula on our reference tables!
q = mCT
This means what?..
q = mCT
•
•
•
•
q = amount of heat absorbed or lost
m = mass in grams
C = specific heat
T = difference in temperature
Back to our problem…
• Question: You mini - pool containing 100,000 g of water
absorbs how many much heat energy when it warms
from 20 °C to 30 °C?
• q = mCT
q = (100,000 g)(4.184 J / g• K) (10 °C) =
q = 4,184,000 Joules!
Rearranging the formula..
• You need to be able to solve for any of the variables in the
equation
q = mCT
Making it easy..
• If we are finding the heat change during the melting or boiling
phases, we can use the Heat of Fusion or the Heat of
Vaporization..
• Why?? Because temperature remains constant during these
periods!
Heat of Fusion and Vaporization
• Heat of Fusion – amount of heat energy required
to melt a unit mass of a substance
• For water : HOF = 334 J/g
• Heat of Vaporization – amount of energy
required to convert a unit mass from liquid to
vapor phase
• For Water: HOV = 2260 J/g
Practice Problem
• How many joules are required to melt 255 g of ice at 0°C?
• q = m x Heat of Fusion
q = 255 g x 334 J/g = 85, 170 J
Measuring Heat Change
 Calorie
= the amount of energy(heat)
required to raise the temperature of one
gram of water by one Celsius degree.
1
Calorie (cal) = 4.184 Joules (J)
Metric system
SI system
Converting Calories to Joules
 Convert
60.1 cal of energy into joules
1 cal = 4.184 J
60.1 cal X 4.184 J =
1 cal
251 J
Converting Joules to Calories

Convert 50.3 J to cal
1 cal = 4.184 J
50.3 J X
1 cal = 12.0 cal
4.184 J
Kilojoules and Kilocalories
 The
prefix kilo means 1000
 energy
is often expressed in kilos because
the numbers are large
 We
can use Dimensional Analysis to
convert.
4.0 J x 1 kJ
1000 J
= 0.0040 kJ
Converting kilojoules to
kilocalories
1 cal = 4.184 J
1000 kcal = 4184 kJ
500.0 kJ x 1000 kcal = 2092 kcal
4184 kJ
Regents Chemistry
• Behavior of Gases
Behavior of Gases
• Scientists construct models to explain the
behavior of substances
• Gas laws are used to describe the behavior of
gases
• We will focus on the kinetic molecular theory,
which describes the relationships among
pressure, volume, temperature, velocity,
frequency and force of collisions
Kinetic Molecular Theory
• Major Ideas:
1. Gases contain particles (usually molecules or atoms) that
are in constant, random, straight-line motion
2. Gas particles collide with each other and with the walls of
the container. These collisions may result in a transfer of
energy among the particles, but there is no net loss of
energy as the result of the collisions.
Said to be “Perfectly Elastic”.
Kinetic Molecular Theory
3. Gas particles are separated by relatively great distances.
because of this, the volume occupied by the particles
themselves Is negligible and need not be accounted for.
4. Gas particles do not attract each other.
Relationship Between Pressure and #
of gas Particles
• Kinetic Molecular Theory explains why gases exerts
pressure
• Gas particles collide with each other and the walls of the
container
• Thus pressure is exerted on the walls
• The greater the number of air particles, the greater the
pressure
• Pressure and number of gas molecules are directly
proportional
Relationship
Between Pressure
and Volume of a Gas
• If you compress the
volume of a container,
the particles hit the
walls more often and
pressure increases.
The reverse is also
true!
Relationship Between Temperature and
Pressure of a Gas
• Temperature of a substance is defined as the
measure of the average kinetic energy of the
particles
• Kinetic Energy is given by the formula KE = ½ mv2
• So, as the temperature rise, the average kinetic
energy of the particles increase
• Increase is not due to mass, but an increase in
velocity of the particles, causing them to hit the
walls of the container with greater force (pressure)
Relationship Between Temperature and
Pressure of a Gas
At constant volume, as the temperature of the gas
Increases, the pressure it exerts increases
Relationship of
Temperature
and Volume of
a Gas
At constant pressure,
As the temp of the gas
Increases, the volume
It occupies increases
Relationship Between Temperature
and Velocity
• As temperature increases, the kinetic energy of the particles
increase
• What causes the increase in temp?
• The increase in velocity of the particles
• The higher the average velocity of the particles, the greater the
temperature
KE = ½
2
mv
Combined Gas Law Equation
P1V1
P2V2
T1
T2
P and V
must be in
the same units
and T must
be in Kelvin!
This law can be used to solve problems involving
the gas properties of temperature(T), volume(V)
and pressure(P), whenever two or more of these
properties are involved
Common Units of Variables
Standard temperature and pressure (STP) is defined as
One atmosphere of pressure and a temperature
of 0 C (273K)
Pressure is defined as force per unit area.
In chemistry, pressure is expressed in units of:
torr, millimeters of mercury (mm Hg), atmospheres (atm)
and kilopascals (kPa).
Normal atmospheric pressure is:
760 torr, 760 mm Hg, 1 atm and 101.3 kPa
Ideal vs. Real Gases
The KMT describes Ideal gases, but real gases
behave differently in two ways
• 1. Real gas particles DO ATTRACT at low
temperatures
• Ex: ozone!
• 2. The volume real gas particles occupy at high
pressures becomes important..
• Real behaves most like ideal at high
temperatures and low pressures
Gas Law Sample Problem
worksheet
Regents Chemistry
 Agenda
2/26/04 Thursday
 Review
Gases worksheet
 Discuss Quiz for tomorrow
 HW: STUDY!
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