6.1 - 6.4 slides student nd

8/3/2019 6.1 - 6.4 Slides Student ND

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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



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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!



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What happens next???


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Law of Conservation of Energy


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


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



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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



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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.



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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


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 =


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)



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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.



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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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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


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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