Transcript Slide 1

 The
ability to do work
 The ability to transfer heat
Two types: Kinetic and Potential
 Energy
do to motion or action
 electromagnetic waves (light), heat,
motion, electrical current,
 A moving truck has the ability to flatten
you - do work on you!
 Energy
due to position (gravitational or
electrical) or chemical bonds
 Stored energy
 Position: boulder at the top of the hill,
water behind a dam, stick of plastique
 Chemical: tank of gas, hamburger
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Death is very likely the single best invention of Life. It is
Life's change agent. It clears out the old to make way for
the new.
Right now the new is you, but someday not too long from
now, you will gradually become the old and be cleared
away. Sorry to be so dramatic, but it is quite true. Your
time is limited, so don't waste it living someone else's
life.
Don't be trapped by dogma — which is living with the
results of other people's thinking. Don't let the noise of
others' opinions drown out your own inner voice. And
most important, have the courage to follow your heart
and intuition.
They somehow already know what you truly want to
become. Everything else is secondary.
 Energy
can
neither be
created nor
destroyed, but
you may change
from one form to
another
 When
energy is changed from one form
to another, some of the energy is
degraded to a lower-quality, more
dispersed energy form
• No reaction can be 100% efficient
• All reactions lose energy (usually as heat)
• Systems only go spontaneously in the direction
of decreasing order (increasing entropy)
• heat always flows from hot to cold
 Entropy
is the amount of disorder in a
system
 Entropy always increases over time (in
the absence of an input of outside
energy)
 example. cleaning up your room
 There
are two units which are commonly used:
 Calories
one
(c): amount of energy it takes to raise
gram of water one degree Celsius
• Calories in food (C) = kilocalories(kcal) = 1000
calories
 Joules
(J): 4.18 Joules = 1 calorie
 Heat
is the amount of kinetic energy of
the atoms
 Temperature
measures the average
speed of the atoms
 Homework
pages 8-9
J Deutsch 2003
20
•AIM
•Heating and Cooling Curves
•DO NOW
•Page 14
 Exothermic
- Potential energy decreases
• Releases energy
• H, change in heat, is negative
• Energy is on the right
 2H2 + O2  2H2O + energy
 Endothermic
- Potential energy increases
• Absorbs energy
• H, change in heat, is positive
• Energy is on the left
 2H2O + energy  2H2 + O2
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A hot pack contains chemicals that can be activated to produce heat. A cold
pack contains chemicals that feel cold when activated.
1.
Based on energy flow, state the type of chemical change that occurs in a hot
pack.
Exothermic
2.
A cold pack is placed on an injured leg. Indicate the direction of the flow of
energy between the leg and the cold pack.
From the leg to the cold pack (Hot to Cold)
3.
What is the Law of Conservation of Energy? Describe how the Law of
Conservation of Energy applies to the chemical reaction that occurs in the hot
pack.
Energy cannot be created nor destroyed. It can only be changed from one
form to another. The heat produced in the hot pack was stored in the
chemical bonds.
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Boiling
Point
Potential energy changes, so
temperature doesn’t
Melting
Point
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AB
• solid warms up (KE/PE constant)
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AB
• solid warms up (KE/PE constant)
BC
• solid melts (KE constant/PE)
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AB
• solid warms up (KE/PE constant)
BC
• solid melts (KE constant/PE)
CD
• liquid warms up (KE/PE constant)
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AB
• solid warms up (KE/PE constant)
BC
• solid melts (KE constant/PE)
CD
• liquid warms up (KE/PE constant)
DE
• liquid boils (KE constant/PE)
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AB
• solid warms up (KE/PE constant)
BC
• solid melts (KE constant/PE)
CD
• liquid warms up (KE/PE constant)
DE
• liquid boils (KE constant/PE)
EF
• gas warms (KE/PE constant)
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As ice melts at standard pressure, its temperature remains at 0°C until
it has completely melted. Its potential energy
(1) decreases
(2) increases
(3) remains the same
J Deutsch 2003
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A sample of water is heated from a liquid at 40°C to a gas at 110°C. The
graph of the heating curve is shown in your answer booklet.
a On the heating curve diagram provided in your answer booklet, label
each of the following regions:
Liquid, only
Gas, only
Phase change
Phase change
Gas Only
Liquid Only
J Deutsch 2003
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b For section QR of the graph, state what is happening to the water
molecules as heat is added.
They move faster, their
temperature increases.
c For section RS of the graph, state what is happening to the water
Their intermolecular bonds
molecules as heat is added.
are breaking, their potential
energy is increasing.
J Deutsch 2003
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What is the melting point of this substance?
J Deutsch 2003
(1) 30°C
(3) 90°C
(2) 55°C
(4) 120°C
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How do we calculate amount
of heat,(Q), if we are not given
a graphic?
Q
= mCT
Q = mHf
Q = mHv
Have
to figure out which one to use
for a given problem.
Depends which section of heating
curve.
Look for hints in the problem.
Calculating Heat Transferred
Simple system: Pure substance in a
single phase. To calculate heat gained
or lost, use:
Q = mCT
•Q = amount of heat transferred
•m = mass of substance
•C = specific heat capacity of the substance
(Table B).
•T = temperature change = Tfinal – Tinitial
Temperature
changed
Temperature
increased
Temperature
decreased
Initial / Start
temperature
Final
temperature
Ending
temperature
From ____ to ____
Water
Amount of energy required to convert
1 gram of a pure substance from the
solid to the liquid phase at the melting
point.
Heat of Fusion
Q = mHf
Use this equation to calculate energy
changes for phase changes between ice
& liquid water at 0C.
Ice
Freezing
Melting
At
0C (for H2O)
At constant temperature
Amount of energy required to convert
1 gram of a pure substance from the
liquid to the gas phase at the boiling
point.
Heat of Vaporization
Q = mHv
Use this equation to calculate energy
changes for phase changes between
steam & liquid water at 100C.
Steam
Boiling
Condensation
At
100C (for H2O)
At constant temperature