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Chapter 6: Energy andChemical Change
Brady and Senese 5th Ed.
Chem 1110: Prof. Deora
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Energy: Definition and Types
Energy is the ability to do work (move mass over
a distance) or transfer heat
Types: kinetic and potential
: the energy of motion
: the stored energy in matter.
E.g. _____________.
: the sum of the kinetic and
potential energy for each particle in the system
6.1 An object has energy if it is capableof doing work 2
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Potential Energy Depends on Position
Potential energy1. can be converted to E.g.:winding of a clock
2. depends on of the object: E.g.: __________________________________
3. P.E. when:
Objects that attract move apart, or
Objects that repel move toward each other
6.1 An object has energy if it is capableof doing work 3
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Uequilibrium
Ucompressed
Uextended
E
nergy
EmaxEmax
Emin
Stretching or squeezing of the spring. The P.E. of the system
is the least at !
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Kinetic Energy: The Energy of Motion
KE = 1 mv2
2
where: m = mass, v = velocity
Energy can be from one moving particle
to another
Collision of particles with particlescauses the particle to speed up while the
molecule to down .think billiards!
6.1 An object has energy if it is capableof doing work 5
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What happens next???
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Law of Conservation of Energy
6.1 An object has energy if it is capableof doing work 7
First Law of Thermodynamics :
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Interconversion of PE and KE
Think Yankees!! Jeter hits the ballthe ball goes up in
the air.Hitting provides the initial Energy.
in P.E. as the ball goes up.
Since Total Energy is the , K.E. __________
Does the mass change?
Then what?? The ball stops in mid-air., point of
Maximum Energy
Then gravity comes into play..So K.E. andP.E. .
Home run!
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Heat and Temperature
Particles are always moving..hence possess
____________________!
The of an object is proportional to the
_____________of its particles, The higher the averageK.E. the _________the temperature.
______or __________is energy transferred betweenobjects caused by differences in their _________until
they reach _______________.
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What is Temperature?
Temperature (T) is ____________ to the ________
______of all particle units: C, F, K
KEaverage= mvaverage2
At a high temperature, most molecules are moving at
_________________
6.2 Internal energy is the total energy ofan objects molecules 10
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A. A pencil rolls across a desk
B. A pencil is sharpened
C. A pencil is heated
D. All are forms of kinetic energy
E. None are forms of kinetic energy
6.1 An object has energy if it is capableof doing work 11
Which of the following is not a
form of kinetic energy?
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Units of Energy
SI unit is the Joule, J J = kgm/s2
If the calculated value is greater than 1000 J, use the kJ
Another unit is the calorie, cal
cal = 4.184 J (exact)
Nutritional unit is the Calorie (note capital C),which is one kilocalorie
1 Cal = 1 kcal = 4.184 kJ
6.1 An object has energy if it is capableof doing work 12
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Internal Energy is Conserved
From the 1st Law of Thermodynamics: For anisolated system the internal energy (E) _________:
E=Ef-Ei = 0
E=Eproduct -Ereactant = 0
We ______ measure the internal energy of
anything, so we measure the ______________
Eis a State Function
6.2 Internal energy is the total energy ofan objects molecules 13
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6.2 Internal energy is the total energy ofan objects molecules 14
State Function A property whose value depends only on the ______
_______________, not on the ______ or ______used to arrive at that state
Position is a State Function: both train and car travel
to the same locations although their paths vary
The actual distance traveled does vary with path
New
York
Los
Angeles
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6.3 Heat can be determined by measuring temperature changes 15
Heat Transfer is a State Function
Transfer of heat during a reaction is a _____
_________.
The route taken to arrive at the products
________affect the ____________ that
is___________.
The number of steps ________ affect the
_______________ that is ___________.
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Heat Capacity and Transfer
Heat capacity(C) - the (extensive) ability of an
object with constant mass to absorb heat.
Calorimeter constant
Varies with the __________ and the _________ of the
substance Units: J C-1
q = Ct
q = C=
t=
6.3 Heat can be determined bymeasuring temperature changes 16
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6.3 Heat can be determined by measuring temperature changes 17
Heat Transfer, q
HeatTransfer (q) - the transfer of energy from
Units: J, cal, kgm2
/s2
A calorie is the amount of energy needed
A metal spoon at 25 C is placed in boiling water.
What happens?
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Surroundings / System / Universe
_______-the reaction or area under study ___________-the rest of the universe
_____________- can gain or lose mass and energy
across their boundaries. E.g. ____________- can absorb or release energy, but
not mass, across their boundaries. E.g.
______________- cannot exchange matter orenergy with their surroundings. E.g.
6.3 Heat can be determined bymeasuring temperature changes 18
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6.3 Heat can be determined bymeasuring temperature changes 19
The Sign Convention
_________________ require energy to beadded to the system, thus the q is (+)
_________________ release energy to the
surroundings. Their q is (-) Energy changes are measured from the point of
view of the system
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A. The water heats
B. The skillet cools
C. The heat transfer for the skillet has a (-) sign
D. The heat transfer for the skillet is the same as
the heat transfer for the water
E. None of these are untrue
6.3 Heat can be determined bymeasuring temperature changes 20
A cast iron skillet is moved from a hot oven toa sink full of water. Which of the following isnot true?
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q = C
tq =
q =
6.3 Heat can be determined bymeasuring temperature changes 21
A cup of water is used in an experiment. Its
heat capacity is known to be 720 J C-1. How
much heat will it absorb if the temperaturechanged from 19.2 C to 23.5 C?
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Heat Transfer and Specific Heat
Specific heat(s) - The intensive ability of asubstance to store heat.
C= ms
Units: J g-1
C-1
or J g-1
K-1
or J mol-1
K-1
q = mts
q = heat transferred
m = mass of object t= change in temperature (tfinal - tinitial)
6.3 Heat can be determined bymeasuring temperature changes 22
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6.3 Heat can be determined bymeasuring temperature changes 23
Specific Heats
Substances with highspecific heats resist
temperature changes
Note that water has a
very high specific
heat
This is why coastal
temperatures aredifferent from inland
temperatures.
Substance
Specific Heat
J g-1C-1(25 C)
Carbon (graphite) 0.711
Copper 0.387
Ethyl alcohol 2.45Gold 0.129
Granite 0.803
Iron 0.4498
Lead 0.128Olive oil 2.0
Silver 0.235
Water (liquid) 4.18
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Calculate the specific heat of a metal if it
takes 235 J to raise the temperature of a
32.91 g sample by 2.53 C.
6.3 Heat can be determined bymeasuring temperature changes 24
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6.3 Heat can be determined bymeasuring temperature changes 25
The First Law of ThermodynamicsExplains Heat Transfer
If we monitor the heat transfers (q) of all
materials involved and all work processes,
_____________________________________ By monitoring the surroundings, we can predict
______________________________
Heat transfers until thermal equilibrium is
achieved, thus the final temperature is ______
_____________________
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6.3 Heat can be determined bymeasuring temperature changes 26
A 43.29 g sample of solid is transferred from boiling water (t
= 99.8 C) to 152 g water at 22.5 C in a coffee cup. The
twater rose to 24.3 C. Calculate the specific heat of the solid.
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A. 870 J/C
B. 35 J/C
C. -35 J/C
D. -870 J/C
E. None of these
6.3 Heat can be determined bymeasuring temperature changes 27
What is the heat capacity of the container if 100. g of
water (s = 4.184 J g-1C-1) at 100. C are added to 100.
g of water at 25 C in the container and the final
temperature is 61 C?
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Chemical Potential Energy
___________: net attractive forces that bindatomic nuclei and electrons together
________________form stronger bonds in the
product than in the reactant and release energy _________________ break stronger bonds in the
reactant and require energy
6.4 Energy is absorbed or releasedduring most chemical reactions 28
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