Law of Conservation of Energy
• States that energy can neither be created
or destroyed or that the total amount of
energy in a system remains constant.
• We can measure the energy in terms of
calories.
Calories
• One calorie is defined as the amount of
energy needed to raise the temperature of
1 gram of water 1oC
• Abbreviated as (cal)
• Dietary calories (C) = 1000cal or 1kcal =
amount of energy released from foods
Heat Energy
• Heat - a flow of energy from a hot object
(higher energy) to a cold object (lower
energy).
– The most familiar form of energy
– All matter contains some heat energy.
– The net energy transferred from or to an
object as a result of a temperature difference
which results in a change in internal energy
Review Heat Energy
The heat energy of a substance is
determined by how active its particles
(atoms and molecules) are.
A hot object is one whose atoms and
molecules are excited and show rapid
movement.
A cooler object's molecules and atoms
will be less excited and show less
movement.
What is Heat Energy?
• As heat is added to an object the
temp. increases
• The added heat becomes part of
the object’s internal energy
Heat travels from a hot object
(higher energy) to a cold object
(lower energy).
So how does heat travel from one
object to another?
By Convection, Conduction and
Radiation.
Heat Transfer by Convection
• Convection occurs only in
liquids and gases.
• We call liquids and gases
fluids.
• It cannot happen in solids.
• It needs particles to be free
to move about.
• A radiator in a room heats
up the room by convection
(NOT radiation).
Heat Transfer by Convection
• Look at the engine
at the left.
• Water carries heat
from a hot engine
through a pump and
delivers it to a
radiator, whose duty
is to give up heat to
the air.
Heat Transfer by Conduction
• The process in which heat passes through
a solid substance is called conduction.
• Metals are good conductors of heat.
• Non-metals are generally bad conductors
of heat.
• Liquids and gases are bad conductors of
heat as well.
• A bad conductor of heat is called an
insulator.
Ability of a metal to conduct heat?
• What is an element of
metal made of?
Atoms that vibrate
Free electrons that move
around
• They are constantly
vibrating or oscillating
against each other.
• Through these collisions,
the heat energy is
conducted
Heat Transfer by Conduction
• The flow of heat from a hot part of a body to a
cooler part, without transfer of matter.
• Can also take place from one body to another,
provided the two bodies are in contact, and a
temperature difference exists between them.
• A pot on a hot plate is heated by conduction
from the stove
surface, via the underside
of the pot.
Heat Transfer by Radiation
• The easiest way to explain heat transfer by
RADIATION is by the heat we feel from the sun or
a light bulb.
• RADIATION of heat is the transfer of heat energy
through matter or space as electromagnetic
waves.
• Examples :
– Electromagnetic waves called infra-red radiation that is
emitted from earth.
– Ultraviolet radiation that is emitted from the sun and
causes sunburns
– Microwaves that cook food
Review
• Heat flows from hot objects to cold
objects.
• Heat flow depends on the temperature
difference.
• Heat is not temperature.
• Heat passes by conduction, convection, or
radiation.
• Radiation is caused by infra-red radiation
Determining the amount of heat
gained or lost by a substance
Step 1
• You will need the following formulas for
your calculations:
– where T refers to the change in temperature
– Tf refers to the final temperature and
– Ti refers to the initial temperature
 T= Tf - Ti
Determining the amount of energy
lost or gained
Step 2
– where Qcal refers to the heat gained (or lost)
expressed in calories
– mass of water is expressed in grams
– (1 mL water = 1 gram)
– T refers to the change in temperature
Qcal  (mass of water)( T)
– Answers are expressed in calories or cal
Qcal  (mass of water)( T)
45 gm sample of water is heated from
24.0ºC to 82.0 ºC
 T= Tf - Ti
How much heat was gained by the cold
water?
∆T = 82.0 – 24.0 = 58.0 ºC
Qcal = 45 g x 58.0 ºC = 2610 = 2600cal
• If a sample of hot water and cold water are
mixed together…
• Based on the Law of Conservation of
Energy what would you expect?
Qcal  (mass of water)( T)
110.5 gm sample of hot water has an initial
temp of 61.8ºC. 250.0 gm of 1.8ºC water
is added to it and the final temperature is
6.8ºC
1 - How much heat was gained or lost by the
by the cold water?
2 - How much heat was gained or lost by the
warm water?
How Do We Measure the
Changes in Heat Energy?
Temperature
What is Temperature?
• The measure of the average kinetic
energy of the particles (atoms and
molecules) of a substance
– Kinetic energy is the energy an object posses
because of it’s motion
How do we measure temperature?
With a thermometer.
1. A thermometer is an instrument that
utilizes the physical property of thermal
expansion for the purpose of accurately
determining temperature
What is thermal expansion?
1. The property of a substance to expand
with an increasing temperature and
contract with a decreasing temperature
2. The expansion and contracting allows for
the quantitative measure of temperature
by using a thermometer.
Thermometer
• Most common is the
bulb type
• As the substance gets
hotter, the particles in
the liquid mover faster
and spread out
• This causes the red
liquid to move up.
• Gives us a
quantitative reading.
3 Different Temperature Scales