Regents Chemistry

1
Regents Chemistry

• Topic IV
• Physical Behavior of Matter

2
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

3
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 planets core!

4
Heating and Cooling Curves

• Heating Curves Constant rate of heating of a
  substance over time endothermic process!

5
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

6
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!
7
Cooling Curves

• Shows the constant rate of cooling of a gas at
  high temperature an exothermic process

8
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

9
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

10
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

11
Practice Problem
Which portions of the graph represent times when
heat is absorbed and potential energy increases
while kinetic energy remains constant?
worksheet
12
Regents Chemistry

• Temperature Scales

13
Temperature Scales

• Celsius C
• Based on boiling point/freezing point of water
  
• Kelvin K
• Based on absolute zero
• Fahrenheit F
• Used in U.S. and Great Britain

14
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
15
Practice Problems

• Convert 10 C to F
• F 9/5(C) 32 9/5 (10 C) 32
• 50F

Convert 25C to K K C 273
16
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)

17
Regents Chemistry

• Measurement of Heat Energy

18
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
  lifes daily functions.
• It comes in many forms!

19
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.

20
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?

21
Specific Heat Capacities

• Check out the specific heat capacities of
  different substances!

22
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

23
This means what?..

• q mC?T
• q amount of heat absorbed or lost
• m mass in grams
• C specific heat
• ?T difference in temperature

24
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!

25
Rearranging the formula..

• You need to be able to solve for any of the
  variables in the equation
• q mC?T

26
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!

27
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

28
Practice Problem

• How many joules are required to melt 255 g of ice
  at 0C?
• q m x Heat of Fusion

q 255 g x 334 J/g 85, 170 J
29
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
30
Converting Calories to Joules

• Convert 60.1 cal of energy into joules
• 60.1 cal X 4.184 J 251 J

1 cal 4.184 J
1 cal
31
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
32
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
0.0040 kJ
1000 J
33
Converting kilojoules to kilocalories
1 cal 4.184 J 1000 kcal 4184 kJ
500.0 kJ x
1000 kcal
2092 kcal
4184 kJ
34
Regents Chemistry

• Behavior of Gases

35
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

36
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.
37
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.
38
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

39
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!

40
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)

41
Relationship Between Temperature and Pressure of
a Gas
At constant volume, as the temperature of the
gas Increases, the pressure it exerts increases
42
Relationship of Temperature and Volume of a Gas
At constant pressure, As the temp of the
gas Increases, the volume It occupies increases
43
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 mv2
44
Combined Gas Law Equation
P and V must be in the same units and T must be
in Kelvin!
P1V1
P2V2
T1
T2
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
45
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

46
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

47
Gas Law Sample Problem
worksheet
48
Regents Chemistry

• Agenda 2/26/04 Thursday
• Review Gases worksheet
• Discuss Quiz for tomorrow
• HW STUDY!

49
1
50
2