Heat Changes

E N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - H

heat content in matter:

E N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - H

heat content in matter:

natural systems tend to go from a state of high energy to a state of low energy.

E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y

The phases of matterrepresent "classes" of molecular motion found at different temperatures.



XKinetic Energ

y



XHEAT


q = U + P Vq = heat gained or lostU = internal energyP = PressureV = volume


Hfus - heat of fusion

As energy is added to a solid at its melting point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.


Hfus - heat of fusion

The amount of heat needed to change one gram of a solid into a liquid at its melting point.

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Heat Added

Tem

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Every phase change isaccompanied by a changein the energy of the system.

As the temperature of a solidincreases, its particle vibration increases.

When a solid melts, itsparticles are freed to move with respect to one another.

This melting process is called fusion.

The increased freedom ofmotion of the molecules orions comes at a price...

measured by the heat of fusion, or enthalpy of fusion, Hfus

As the temperature of a liquidincreases, the molecules movewith increasing energy.

When increasing temperature,the concentration of gas-phasemolecules just above thesurface of the liquid increases.

These gas-phase moleculesexert a pressure on theliquid called vapor pressure.

This vapor pressure increases with temperature until it equals the atmospheric pressure.

This is the boilingpoint of the liquid.

The energy required tocause this transition..

is called the heat of vaporization or enthalpy of vaporization, Hvap

solid/liquid phase change

q = m Hfus

q = heat gained or lostm = massHfus = heat of fusion


Hfus H2O = 334 J/g

Hfus lead = 24.72 J/g


As energy is added to a liquid at its boiling point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.


Hvap - heat of vaporization

The amount of heat needed to change one gram of a liquid into a gas at its boiling point.

liquid/gas phase change

q = m Hvap

q = heat gained or lostm = massHvap = heat of vaporization


Hvap H2O = 2260 J/g

change temp within change temp within phasephase

q = m Cp

q = heat gained or lostm = mass= “change in temperature”

Cp = specific heat capacity

Specific Heat Specific Heat CapacityCapacity


The heat required to raise

the temperature of onegram of a substance byone Celsius degree.



Cp of ice = 2.06 J/g.Co

Cp of water = 4.18 J/g.Co

Cp of steam = 2.02 J/g.Co

Cp of copper = .385 J/g.Co

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q=mHvap - change phase

q=mHFUS- change phase

q=mCp - change temp

q=mCp - change temp

q=mCp - change temp

Heat of Fusion of Ice

How much heat is needed toconvert 250 grams of ice at -30 oC to vapor at 150 oC?

1. Change temp of ice2. Melt ice3. Change temp of liquid water4. Vaporize water5. Change temp of vapor6. Add total heat used

Step 1 raise temp of ice

q = m T Cp

q = (250g) (30 Co) (2.06 J/g. Co)

q = 15,450 JoulesQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Step 2 melt ice

q = m Hfus

q = (250g) (334 J/g)



Step 3 raise temp of liquid water

q = m T Cp

q = (250g) (100 Co) (4.18 J/g. Co)



Step 4 vaporize liquid water

q = m Hvap

q = (250g) (2260 J/g)



Step 5 raise temp of water vapor

q = m T Cp

q = (250g) (50 Co) (2.02 J/g. Co)



Step 6

q = 15,450 83,500 104,500 565,000 25,250



What is

Which has the greater?

Fe H2Oor

Specific Heat Capacity - 13 min

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is used to measure

heat change

Calorimetry - 13 min

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Specific Heat of a Metal

Lab Burners and BTUs

P h a s e D i a g r a mP h a s e D i a g r a m

A g r a p h s h o w i n g A g r a p h s h o w i n g t h e p h a s e s o f t h e p h a s e s o f m a t t e r a s t h e m a t t e r a s t h e y r e l a t e t o y r e l a t e t o t e m p e r a t e m p e r a t u r e a n d t u r e a n d p r e s s u r e . p r e s s u r e .

M a j o r p o i n t s o n a p h a s e d i a g r a m

M a j o r p o i n t s o n a p h a s e d i a g r a m

Normal Atmospheric PressureNormal Atmospheric Pressure

Triple pointTriple point

Boiling PointBoiling Point

Melting pointMelting point

Critical temperatureCritical temperature

101.325 kPanormal atmospheric pressure

TP Triple Point

Tb

Normal boiling point

Tm

Normalmelting point

Tc

Criticaltemperature

V a n d e r W a l l s A t t r a c t i o n

V a n d e r W a l l s A t t r a c t i o n

T h e f o r c e o f T h e f o r c e o f a t t r a c t i a t t r a c t i o n o n b e t w e e n b e t w e e n

m o l e c u l e sm o l e c u l e s

Calories in a Peanut

Heat Changes

Documents

p yhfus heat

heat of fusione n t

heat of vaporizatione

p yhvap heat

volumee n t h

xheate n t h

jge n t h

xkinetic energye n t