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Energy and States of Matter
(Thermochemistry)
Measuring Heat Energy
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HEAT
HEAT
HEAT
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HEAT
Heat
Energy that flows from something warm to
something cooler. (Heat flows from high to low!)
A hotter substance gives KE (kinetic energy) to a
cooler one
When heat is transferred (lost or gained), there is
a change in the energy within that substance
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HEAT VS. TEMPERATURE
Heat & temperature are NOT synonyms
 Heat is energy that transfers from one object to
another because of a temperature difference
between the objects.
 Remember that temperature is defined as a
measure of the average kinetic energy of
particles in matter
So, the Kinetic Energy defines the temp.:
 Particles moving/vibrating fast = HOT
 Particles moving/vibrating slow = COLD
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HEAT
DEFINITION
THE FLOW OF THERMAL ENERGY
FROM SOMETHING WITH A HIGHER
TEMP TO SOMETHING WITH A LOWER
TEMP
UNITS
Joules (J) OR calories (cal)
TYPES
THROUGH WATER OR AIR =
CONVECTION
THROUGH SOLIDS = CONDUCTION
TRANSFERRED ENERGY BY
COLLISION WITH PHOTON =
RADIANT ENERGY
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Practice1
A. When you touch ice, heat is transferred
from
1) your hand to the ice
2) the ice to your hand
B. When you drink a hot cup of coffee,
heat is transferred from
1) your mouth to the coffee
2) the coffee to your mouth
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Practice2
When you heat 200 g of water for 1 minute, the
water temperature rises from 10°C to 18°C.
400 g
200 g
If you heat 400 g of water at 10°C in the same pan
with the same amount of heat for 1 minute, what
would you expect the final temperature to be?
1) 10 °C
2) 14°C
3) 18°C
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Practice2
When you heat 200 g of water for 1 minute, the
water temperature rises from 10°C to 18°C.
400 g
200 g
If you heat 400 g of water at 10°C in the same pan
with the same amount of heat for 1 minute, what
would you expect the final temperature to be?
1) 10 °C
2) 14°C
3) 18°C
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Reasoning
Heating twice the mass of water using the
same amount of heat will raise the
temperature only half as much.
400 g
200 g
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Some Equalities for Heat
Heat is measured in calories or joules
 1 kcal = 1000 cal
 1 calorie = 4.18 J
 1 kJ = 1000 J
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calories and Calories
 A calorie is defined as the quantity of heat needed to
raise the temperature of 1 gram of pure water by 1oC
Abbreviation = cal with small c.
 There is a difference between a calorie and a Calorie
 calorie is defined above and is used except when
referring to the energy contained in food.
 Calorie = refers to energy in food
 1 Calorie = 1 kilocalorie = 1000 calories
↑
(in food)
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Calories and Calories
 A calorie is defined as the quantity of heat needed to
raise the temperature of 1 gram of pure water with
1oC
Abbreviation = cal with small c.
 There is a difference between a calorie and a Calorie
 calorie is defined above and is used except when
referring to the energy contained in food.
 Calorie = refers to energy in food
 1 Calorie = 1 kilocalorie = 1000 calories
↑
(in food)
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Joule
 Joule = is the SI unit of heat and energy
named after the English physicist James
Prescott Joule (1818-1889)
 Equivalence statements:
1J = 0.2390 cal
1 cal. = 4.18 J
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Specific Heat : c or Cp
Why do some foods stay hot longer than others?
Why is the beach sand hot, but the water is cool
on the same hot day?
Why do your scrambled eggs get cold so fast
while the pancakes stay warm for much longer?
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Specific Heat (Cp) Values
Specific heat is the amount of heat needed
to raise the temperature of 1 g of a
substance by 1°C
cal/g°C J/g°C
water
1.00
4.18 memorize!
aluminum
copper
silver
gold
0.22
0.093
0.057
0.031
0.90
0.39
0.24
0.13
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Specific Heat : Cp or c
 Specific heats are listed on data tables
The smaller the specific heat  the less energy
it takes the substance to feel hot
 The larger the specific heat  the more energy
it takes to heat a substance up
 The smaller the specific heat  the less time it
takes the substance to cool off
 The larger the specific heat  the longer time it
takes the substance to cool off

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Practice3
A. A substance with a large specific heat
1) heats up quickly 2) heats up slowly
B. When ocean water cools, the surrounding air
1) cools
2) warms 3) stays the same
C. 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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All chemical reactions involve an
energy change.
The transfer of energy, usually heat, into or out of
the reaction mixture.
For example:


When petroleum burns, heat is given out.
When ammonium nitrate dissolves in water, heat
is taken in.
Instead of writing ‘enthalpy change’ all
the time, chemists use the symbols:
ΔH
Pronounced ‘delta H’.
Δ = Greek letter ‘delta’ meaning change.
H = enthalpy (see below)
So, ΔH means ‘change in enthalpy’.
(Enthalpy is the heat content of a system;
assuming pressure is constant)
Temperature Changes 1
Some reactions cause the
temperature of the reaction mixture
to increase.
This type of reaction is called
exothermic.
Heat energy is given out by the
reaction so the reaction feels hot.
Temperature Changes 2
Some reactions cause the
temperature of the reaction mixture
to decrease.
This type of reaction is called
endothermic.
Heat energy is taken in by the
reaction so the reaction feels cold.
Representing Energy Changes:
The energy changes in a chemical reaction
can be conveniently represented using
energy level diagrams
Energy level diagrams make it easier to
decide whether a reaction is exothermic or
endothermic
See next slide for some examples.
Energy Level Diagrams (copy this!)
This energy level diagram
shows a reaction where ΔH
is negative (an exothermic
reaction).
ΔH negative,
exothermic.
This energy level diagram shows a
reaction where ΔH is positive (an
endothermic reaction).
ΔH positive,
endothermic.
Making and Breaking Bonds:
Breaking chemical bonds is always endothermic.
Making chemical bonds is always exothermic.
All chemical reactions involve bond ‘rearrangements’.
Bonds are broken and new ones are formed.
Chemical reactions are in two stages:
1. Breaking bonds, an endothermic process.
2. Making new bonds, an exothermic process.
Summary
Chemical reactions happen in two stages:
1. Breaking bonds, an endothermic process.
2. Making new bonds, an exothermic process.
Exothermic rxns get hot, they give out heat.
Endothermic rxns get cold, they take in heat.
(think about that for a second)
The energy changes in a chemical reaction can
be represented using energy level diagrams and
reaction profile diagrams.
Law of Conservation of Energy
Law of Conservation of Energy, also called
The First Law of Thermodynamics
 In any chemical or physical process,
energy is neither created nor destroyed it is
conserved. All the energy involved in a
process can be accounted for work, energy,
or heat.
-q lost= q absorbed
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Measuring Heat Energy ( q )
Requires
 Grams of substance
 Temperature change T
 Specific heat of the substance (c)
is shown as “Cp” on your periodic table
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Heat Capacity
 Heat capacity is the amount of heat needed to increase
the temperature of an entire object by exactly 1°C
 q = mc∆T
 heat = (mass)(specific heat)(change in temperature)
 units: (grams)( cal OR Joules) (°C)
g°C
g°C
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Heat Capacity
 Heat capacity is the amount of heat needed to increase
the temperature of an entire object by exactly 1°C
 q = mc∆T
 heat = (mass)(specific heat)(change in temperature)
 units: (grams)( cal OR Joules) (°C)
g°C
g°C
 Therefore units of heat would be cal or J depending on
the specific heat value used.
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Heat Calculations
A hot-water bottle contains 750 g of water at 65°C. If the
water cools to body temperature (37°C), how many
calories of heat could be transferred to sore muscles?
q= m x c (of H2O) x T
750 g x 1.00 cal x 28°C
g°C
= 21,000 cal
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Heat Calculations
A hot-water bottle contains 750 g of water at 65°C. If the
water cools to body temperature (37°C), how many
joules of heat could be transferred to sore muscles?
q= m x c (of H2O) x T
750 g x 4.18 J x 28°C
g°C
= 87,760J
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Practice4
How many kcal are needed to raise
the temperature of 120 g of water
from 15°C to 75°C?
1) 60 kcal
2) 7.2 kcal
3) 9.0 kcal
4) 7200 kcal
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Solution
How many kcal are needed to raise
the temperature of 120 g of water
from 15°C to 75°C?
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Answer
How many kcal are needed to raise
the temperature of 120 g of water
from 15°C to 75°C?
1) 60 kcal
2) 7.2 kcal
3) 9.0 kcal
4) 7200 kcal
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Energy and Nutrition
1 Calorie (nutritional) = 1 kcal
1 Cal
= 1000 cal
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CALORIMETRY

Calorimetry is the process of measuring heat energy



Measured using a device called a calorimeter
Uses the heat absorbed by H2O to measure the heat given off by
a rxn or an object
The amount of heat absorbed (or lost) by the water is
equal to the amount of heat released (or gained) by the
reaction or object
HSYS= -HSUR
Hsys is the system or what is taking place in the main
chamber (rxn etc.) &
Hsur is the surroundings which is generally water.
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A COFFEE CUP
CALORIMETER
USED FOR A
REACTION IN WATER,
OR JUST A TRANSFER
OF HEAT.
A BOMB CALORIMETER
USED WHEN TRYING
TO FIND THE AMOUNT
OF HEAT PRODUCED BY
BURNING SOMETHING
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Phase Changes Quiz
●Draw
a diagram showing all of the phase
changes for water. Label the 3 states of
matter, the names of the phase change
processes, and whether each process is
exothermic or endothermic.
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Phase Change Diagram with names of changes and
Exothermic vs. endothermic
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*Water’s state of matter changes at certain
temps because heat is being gained or lost
*Particles move closer or spread apart more
from kinetic energy
*Sublimation-solid to gas
*Deposition-gas to solid
*They skip the liquid phase
Latent Heat of …
●ΔH
Fusion(melting)
●ΔH Solidification
●ΔH Vaporization
●ΔH Condensation
●ΔH Sublimation
●ΔH Deposition
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Latent Heat of … for Water
●ΔH
Fusion(melting) = 80 cal /g or 334 J / g
●ΔH Solidification = 80 cal /g or 334 J / g
●ΔH Vaporization = 540 cal /g or 2260 J / g
●ΔH Condensation = 540 cal /g or 2260 J / g
●ΔH Sublimation = ? cal /g or ? J / g
●ΔH Deposition = ? cal /g or ? J / g
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Calculate the amount of heat in Joules
required to melt 28 grams of ice
• Q=mΔHfusion
• Q=28g (334 J/g)
• Q=9352 J
Calculate the amount of heat in Joules needed
to freeze 155 grams of water
Q=mΔHfreezing (opposite of fusion)
Q=155g (334 J/g)
Q=51770 J
Calculate the amount of heat in calories
needed to vaporize 506 grams of ice
Q= mΔHvaporization
Q= 506g (540 cal/g)
Q= 273240 cal
Calculate the amount of heat released in
calories when 34 grams of water goes through
condensation.
Q= mΔHcondensation (opposite of vaporization)
Q=m (540cal/g)
Q = 34g (540 cal/g)
= 18360 J