Transcript Chapter 2

Chapter 2
Matter and Energy
2.1 Classification of Matter
Matter is anything that has mass and
occupies space.
 Classification of matters are

◦ Pure substance
◦ Mixture
Pure substance

Has fixed or definite composition
◦ An element, the simplest type of pure
substance and is composed of atoms
 E.g.
H, Na, O, C etc…
◦ A compound consists of atoms of two or
more elements
 Chemically combined in proportion and held
together by a bond
 E.g. H2O, NaCl, CO2 etc…
Mixtures

Two or more substances are physically
mixed, not chemically combined.
◦ Homogeneous mixture or solution
 Has a uniform composition
 E.g. air contains oxygen and nitrogen
◦ Heterogeneous mixture
 Does not have a uniform composition
 E.g. raisins in cookie
2.2 States and Properties of Matters
Solids have
• a definite shape.
• a definite volume.
• particles that are close
together in a fixed
arrangement.
• particles that move very
slowly.
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2.2 States and Properties of Matters
Liquids have
• an indefinite shape, but
a definite volume.
• the same shape as their
container.
• particles that are close
together, but mobile.
• particles that move
slowly.
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2.2 States and Properties of Matters
Gases have
• an indefinite shape.
• an indefinite volume.
• the same shape and
volume as their
container.
• particles that are far
apart.
• particles that move very
fast.
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Summary of the States of Matter
Table 2.1
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2.2 States and Properties of Matters
Physical Properties: Characteristics that do
not involve a change in a sample’s chemical
makeup.
 Chemical Properties: Characteristics that do
involve a change in a sample’s chemical makeup.

2.2 States and Properties of
Matters
Physical change occurs when matter
changes its appearance but the
composition stay the same
 Chemical change takes place when the
original substance is converted into
one or more new substances

◦ Have different physical and chemical
properties
Examples
Identify each as: 1) solid, 2) liquid, or 3) gas.
A. It has a definite volume, but takes the shape of
the container.
__ B. Its particles are moving rapidly.
__ C. It fills the volume of a container.
__ D. It has particles in a fixed arrangement.
__ E. It has particles close together that are mobile.
___
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Example

What type of change, physical or
chemical, takes place in the each of the
following
◦
◦
◦
◦
Water vapor condenses to form rain
Cesium metal reacts explosively with water
Gold melts at 1064 oC
Food is digested
Energy
Energy
• makes objects move.
• makes things stop.
• is needed to “do work.”
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Work
Work is done when
• you climb.
• you lift a bag of
•
•
•
•
groceries.
you ride a bicycle.
you breathe.
your heart pumps blood.
water goes over a dam.
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Potential Energy
Potential energy is
• stored energy.
Examples are
•
•
•
water behind a dam.
a compressed spring.
chemical bonds in
gasoline, coal, or food.
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Kinetic Energy
Kinetic energy is the
• energy of motion.
Examples are
•
•
•
•
swimming.
water flowing over a dam.
working out.
burning gasoline.
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Units for Measuring Energy or
Heat
Heat is measured in joules or calories.
4.184 Joules (J) = 1 calorie (cal)
1 kJ = 1000 J
1 kilocalorie (kcal) = 1000 calories (cal)
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Examples of Energy In Joules
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Examples
Identify the energy as potential or kinetic.
A.
B.
C.
D.
Rollerblading
a peanut butter and jelly sandwich
mowing the lawn
gasoline in the gas tank
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Example

The energy needed to keep a 75-watt light bulb
burning for 1.0h is 270KJ. Calculate the energy
required to keep the light bulb burning for 3.0 h in
each of the following energy units:
a. Joules
b.
kilocalories
2.3 Temperature Conversion
• Temperature is a measure of how hot or cold an
object is compared to another object.
• indicates that heat flows from the object with a higher
temperature to the object with a lower temperature.
• is measured using a thermometer.
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Temperature Scales
• are Fahrenheit,
Celsius, and
Kelvin.
• have reference
points for the
boiling and
freezing points
of water.
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Examples
A. What is the temperature of freezing water?
1) 0 °F 2) 0 °C
3) 0 K
B. What is the temperature of boiling water?
1) 100 °F
2) 32 °F
3) 373 K
C. How many Celsius units are between the boiling
and freezing points of water?
1) 100
2) 180
3) 273
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Fahrenheit Formula
• On the Fahrenheit scale, there are 180 °F between the
•
freezing and boiling points; on the Celsius scale there
are 100 °C.
180 °F = 9 °F =
1.8 °F
100 °C
5 °C
1 °C
In the formula for the Fahrenheit temperature,
adding 32 ° adjusts the zero point of water from 0 °C to
32 °F.
TF
= 9/5 TC + 32 
TF
= 1.8 TC + 32 
or
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Celsius Formula
• TC is obtained by rearranging the equation for TF.
TF = 1.8TC + 32 °
• Subtract 32 ° from both sides.
TF - 32 °
=
1.8 TC ( + 32 ° – 32 °)
TF - 32 ° =
1.8 TC
• Divide by 1.8 = °F - 32 °
1.8
TF - 32 °
1.8
=
= 1.8 TC
1.8
TC
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Solving A Temperature Problem
A person with hypothermia has a
body temperature of 34.8 °C.
What is that temperature in °F?
TF
= 1.8 TC + 32 
TF = 1.8 (34.8 °C)
exact 3 SFs
+ 32 °
exact
= 62.6 + 32 ° (addition)
= 94.6 °F
tenth’s
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Kelvin Temperature Scale
The Kelvin temperature scale
• has 100 units between the freezing and boiling points
of water.
100 K = 100 °C or
1 K = 1 °C
• is obtained by adding 273 to the Celsius temperature.
TK
= TC + 273
• contains the lowest possible temperature, absolute
zero (0 K).
0K
= –273 °C
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Learning Check
The normal body temperature of a chickadee is 105.8 °F.
What is that temperature on the Celsius scale?
1) 73.8 °C
2) 58.8 °C
3) 41.0 °C
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Examples
A pepperoni pizza is baked at 455 °F. What
temperature is needed on the Celsius scale?
1) 423 °C
2) 235 °C
3) 221 °C
and in the Kelvin scale?
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2.5 Specific Heat
Specific heat
• is different for different substances.
• is the amount of heat that raises the temperature of 1 g
of a substance by 1 °C.
• in the SI system has units of J/g °C.
• in the metric system has units of cal/g °C.
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Examples of Specific Heats
TABLE 2.7
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Examples
A. When ocean water cools, the surrounding air
1) cools. 2) warms.
3) stays the same.
B. Sand in the desert is hot in the day, and cool
at night. Sand must have a
1) high specific heat.
2) low specific heat.
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Heat Equation
The amount of heat lost or gained by a substance is
calculated from the
• mass of substance (g).
• temperature change (ΔT).
• specific heat of the substance (J/g C).
This is expressed as the heat equation.
Heat = mass x specific heat x ΔT
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Example
How many kJ are needed to raise the temperature
of 325 g of water from 15.0 °C to 77.0 °C?
1) 20.4 kJ
2) 77.7 kJ
3) 84.3 kJ
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Example

Calculate the Calories of one stalk of celery that
produces energy to heat 505 g of water from 25.2oC
to 35.7oC
Example
What is the specific heat if 24.8 g of a metal
absorbs 275 J of energy and the temperature rises
from 20.2 °C to 24.5 °C?
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Examples
How many kcal are absorbed by ocean water if 3
x 1018 L of water in the Caribbean has an increase
of 1 °C. Assume the specific heat of ocean water is
the same as water. Assume the density of ocean
water is 1.0 g/mL.
1) 3 x 1015 kcal
2) 3 x 1018 kcal
3) 3 x 1021 kcal
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2.6 Energy and Nutrition


Energy Values in
Nutrition
◦ 1 Cal = 1 kcal = 1000
cal
◦ 1 Cal = 4.184 kJ =
4184 J
The number of
Calories in a food is
determined by using
an apparatus called a
calorimeter
Energy Value for Foods

The energy (caloric) value of food are the
kilocalories or kilojoules obtained from burning 1g
of carbohydrate, fat or protein.
Table 2.8 Typical Energy (caloric) values of the
three food types
Examples

At a fast-food restaurant, a hamburger contains 37g
of carbohydrate, 19g of fat, and 24g of protein.
What is the total energy content in kilocalories?
Round off the answer to the tenth place
Example

Using the energy values for food (Table 2.8),
determine the grams of fat in one avocado that has
405 kcal, 13g of carbohydrate and 5g of protein.
Round the answer to the tenth place
2.7 Changes of State
A substance
• is melting while it changes from a solid to a liquid.
• is freezing while it changes from a liquid to a solid.
• such as water has a freezing (melting) point of 0 °C.
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Calculations Using Heat of Fusion
The heat of fusion
• is the amount of heat released when 1 gram of
liquid freezes (at its freezing point).
• is the amount of heat needed to melt 1 gram of a
solid (at its melting point).
• for water (at 0 °C) is
80. cal
1 g water
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Calculation Using Heat of Fusion
The heat needed to freeze (or melt) a specific mass
of water (or ice) is calculated using the heat of
fusion.
Heat = g water (ice) x 80. cal
1 g water (ice)
Example: How much heat in cal is needed to melt
15. g of ice?
15. g ice x
80. cal
1 g ice
= 1200 cal
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Examples
A. How many calories are needed to melt 5.0 g of ice
at 0 °C?
1) 80. cal
2) 4.0 x 102 cal
3) 0 cal
B. How many calories are released when 25 g of
water at 0 °C freezes?
1) 80. cal
2) 0 cal
3) 2.0 x 103 cal
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Sublimation
Sublimation
• occurs when particles
change directly from
solid to a gas.
• is typical of dry ice, which
sublimes at -78 C.
• takes place in frost-free
refrigerators.
• is used to prepare freezedried foods for long-term
storage.
Copyright © 2009 by Pearson Education, Inc.
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Evaporation and Condensation
Water
• evaporates when molecules on the surface gain
sufficient energy to form a gas.
• condenses when gas molecules lose energy and
form a liquid.
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Boiling
At boiling,
• all the water molecules
acquire enough energy
to form a gas.
• bubbles appear
throughout the liquid.
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Heat of Vaporization
The heat of vaporization is the amount of heat
• absorbed to vaporize 1 g of a liquid to gas at the
boiling point.
• released when 1 g of a gas condenses to liquid at the
boiling point.
Boiling Point of Water = 100 °C
Heat of Vaporization or condense (water)
=
540 cal
1 g water
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Examples
How many kilocalories (kcal) are released when 50.0 g
of steam from a volcano condenses at 100 °C?
1) 27 kcal
2) 540 kcal
3) 2700 kcal
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Summary of Changes of State
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Heating Curve
A heating curve
• illustrates the changes
of state as a solid is
heated.
• uses sloped lines to
show an increase in
temperature.
• uses plateaus (flat
lines) to indicate a
change of state.
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Examples
A. A flat line on a heating curve represents
1) a temperature change.
2) a constant temperature.
3) a change of state.
B. A sloped line on a heating curve represents
1) a temperature change.
2) a constant temperature.
3) a change of state.
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Cooling Curve
A cooling curve
• illustrates the changes
of state as a gas is
cooled.
• uses sloped lines to
indicate a decrease in
temperature.
• uses plateaus (flat
lines) to indicate a
change of state.
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Examples
Use the cooling curve for water to answer each.
A. Water condenses at a temperature of
1) 0 °C.
2) 50 °C.
3) 100 °C.
B. At a temperature of 0 °C, liquid water
1) freezes.
2) melts.
3) changes to a gas.
C. At 40 °C, water is a
1) solid.
2) liquid.
3) gas.
D. When water freezes, heat is
1) removed.
2) added.
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Combined Heat Calculations
To reduce a fever, an infant is packed in 250. g of ice. If the
ice (at 0 °C) melts and warms to body temperature (37.0
°C), how many calories are removed from the body?
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Example

How many kilojoules of heat are released when 75g
of steam at 100. oC is converted to ice at 0oC?