Count Rumford

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Count Rumford

• Movement of molecules and heat

People thought heat was a liquid
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Heat as a kind of liquid???
caloric
A kind of plasma

• You can transfer heat from one area to another by
  placing objects together.

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Heat is a Form of Motion An Experiment in Boring
Cannon
Count Rumford 1798

• It frequently happens that in the ordinary
  affairs and occupations of life opportunities
  present themselves of contemplation some of the
  most curious operations of nature

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He invented a number things including the

• Rumford Fireplace
• Photometer
• Kitchen range
• Drip coffeepot
• Double boiler

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Sign up for AP chem
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8 block go over percent yeild
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• Finish the lab
• I want the
• CONCLUDING QUESTIONS FOR THE IRON-COPPER (II)
  CHLORIDE LAB
• sheet filled out including the half page
  conclusion mentioned in item 6

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Terms1) system the area under study2)
surroundings the area outside the system3)
Open system system can transfer both energy and
matter to surroundings4) closed system system
where energy can but matter can not be
transferred to surrounding5) isolated system
system can not tansfer either energy or matter6)
exothermic - system where energy is going from
the system to surrounding7) endothermic -
system where energy is going from the surrounding
to the system
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Heat is transfer of energy from one object to
another

• The amount of heat is a combination of the
  temperature of an object and the mass of the
  object.

Temperature is a reflection of the random motion
of the atoms
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Temperature is the average kinetic energy or
velocity of a group of atoms.

• Heat is the total kinetic energy in a system

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A gram of water 22 degrees and a gallon of water
at 20 degrees
which one has a higher temperaturewhich one has
a higher heat content
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It is easy to see which has a greater temperature
but how do we determine which has a greater heat
content?
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Show movie Eureka
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Work is force over distance
Pushing without movement is not work, you are
just applying force
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Keep in mind that what ever we do energy content
is in reference to the system

• Endothermic ?E
• Exothermic - ?E
• Increase of heat (of the system) ?E
• Decrease in heat (of the system) - ?E
• Work is done on the system ?E
• The system does work on the surroundings - ?E

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The energy of a system is influenced by heat
added or removed and by work either done on or
by the system
If heat is added to the system the ?E of the
system increases If heat is removed from the
system the ? E of the system decreases
If work is done on the system the ?E of the
system increases (either increases the potential
energy or kinetic energy) If work is done by the
system on the surroundings then the ?E of the
system decreases (the system is increases the
potential energy or kinetic energy of the
surroundings)
?E q w
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?E q wq is heat w is work

• If you add heat (q) or work is done on the
  system (w) the ?E
• is
• If you remove heat (-q) or the system performs
  work on its surroundings (-w) then the ?E
• is -

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During a chemical reaction such as CH4 2O2 ?
CO2 2H2O Heat

• This means energy in the form of heat left the
  system. exothermic

Where did the energy come from?
Some of the potential energy that was held in the
chemical bonds of the CH4 was released as kinetic
energy (thermal energy) or heat
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Energy diagram
Exothermic Products have less PE
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Energy diagram
Endothermic Products have more PE
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We can not know how much Total Energy anything
contains

• To know how much energy this book has in it we
  have to add all the possible energies kinetic
  (moving earth) and potential (the paper was
  first obtained from the Ohio valley)

We can not know the total energy of an object
just the change in energy ?E i.e. it increased
in temperature it decreased in temperature
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The Change in the internal energy of a system is
the sum of the heat work
?E q w
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I can see how heat enters and leaves a system but
what about work?

• I dont see how a chemical reaction does work!!!

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Pressure and work

• A common type of work associated with chemical
  process is done by a gas in a system or to a gas
  in a system.

Gas engine vs a diesel engine
http//chemed.chem.purdue.edu/genchem/topicreview/
bp/ch5/work.html
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What kind of system is this?
Isolated system
Calorimeter
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The work component of the equation w P?Vp is
the pressure?V is the change in volume
If the work is being done on the system the work
(w) is positive (increase pressure on the
system) If the work is being done to the
surrounding by the system the work w is negative
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During a chemical reaction in a open container
what is the change in pressure or volume?
P 0 Volume 0
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Realizing that W P?Vif there is no pressure
change or volume change thenW 0 and our
equation become
?E q or enthalpy
Not ?E q w but
This is important because most of the experiments
are done in open air so the energy change is
called change of enthalpy or ?H the heat
at 1 atm or enthalpy
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Enthalpy of a system is a state function

• A state function means that the value does not
  take into account what route was taken to get to
  a particular point just what you ended up with.
  The value is the endpoint without referance to
  how you got there.

I was winning 200 dollars at one point but now I
am down 20 bucks The bottom line is you lost 20
bucks
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The simple synthesis of C and O2 C O2 ? CO2
?H -393.5 kJ

• The two step formation of CO2
• C ½ O2 ? CO ?H -110.5 kJ
• CO ½ O2 ? CO2 ?H -283.5 kJ
• C ½ O2 CO ½ O2 ? CO CO2

C O2 ? CO2 ?H -393.5 kJ
A state function has a value that is unrelated of
how you got there
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All energy changes in this course will be with an
open system with constant pressure thus all
energy will be involve a change of enthalpy ?H
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Heat of a system when the volume does not change
and the pressure remains at 1 atm is equal to
Enthalpy?H Hproducts - Hreactants
Think of money and a date

• Like other forms of energy we can not know the
  exact amount of energy something has only the
  change in energy
• ?H

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Example 1When 1 mole of CH4 is burned at
constant pressure and volume, (enthalpy, H)890 kJ
of energy is released as heat. Calculate ?H for
a process in which a 5.8 g sample of CH4 is
burned.
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Example 2
C O2 ? CO2 ?H -393.5 kJ

• The above equation indicates how many kJ of
  enthalpy (heat) in an open chamber is released
  for every mole of carbon dioxide produced from
  Carbon and oxygen gas. If we need to heat a fire
  alarm in order to warn the world that Lex Luthor
  (arch enemy of Superman) is on the loose, how
  many grams of carbon do we need to burn to
  activate the 1000 kJ alarm.

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Heat is based on the speed of the molecules and
the number of molecules present

• Heat is an extensive property This means that
  the size of the object effects the temperature
• A glass of water is 100 degrees low heat
• A Pitcher of water is 100 degrees high heat

Momentum is extensive the mass of the object
effects the momentum
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The higher the temperature the faster the samples
molecules move

• Temperature is an Intensive property This means
  that the size of the object does not effect the
  temperature
• A small glass of water is 100 degrees
• A Pitcher of water is 100 degrees

speed is intensive the mass of the object
doesn't effect the speed
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How Energy is measured in joules or calories

• One calorie is the amount of heat necessary to
  raise one gram one degree
• one Calorie is equal to 4.1 joules. the amount
  of energy to raise one gram on degree centigrade
  is 4.1 joules

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Joules are typically written in kJ or kilojoules

• 1 Calorie 4.18 joule

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• A joule J is a very small number
• The energy to bring a cheeseburger to your mouth
  is a joule

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As we burn natural gas heat is radiated off the
burning gas and that heat causes molecules to
move in the end of the metal.
Heat a piece of metal

• domino effect

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How do we measure heat?

• With a thermometer invented by a guy named
  Fahrenheit

How does a thermometer work
Gases expand, so does mercury
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Fahrenheit used a scale that went from 32 degrees
freezing to 212 boiling

• A different scale was proposed by a guy named
  Celsius that was labeled with 0 being freezing
  and 100 being boiling.

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Because there was 100 increments between
freezing and boiling it is refereed to the
centigrade scale.
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Heat capacityis the amount of heat required to
change a substances temperature by one degree.
The heat capacity is an extensive variable and
so the mass of the substance must be stated
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A more useful quantity is specific heat
capacityJ/Cogram ormolar heat capacity
J/Comole
Specific heat of water is 4.18 J/Co g Specific
heat of aluminum is .89 J/Co g This means that
it takes a little over 4.1 joules to raise one
gram of water 1Co and .89 joules to raise on
gram of aluminum 1Co
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THE CAPACITY OF A SUBSTANCE TO ABSORB HEAT

• Some things get hot fast
• Others things take for ever to warm up

The tendency for a material to absorb heat is
known as a materials specific heat.
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Mass vs Number of particles

• Molar heat capacity mole
• Specific Heat capacity gram

What is the difference???
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The reason why water takes so much energy to get
the molecules moving is those wild hydrogen bonds

• Hydrogen bonds act like shock absorbers and make
  it so it takes more energy for the water molecule
  to start moving.
• But once they start moving they keep going
• Hot water bottle

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Things with low specific heats got hotter faster
Wood or Metal
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We are going to use specific heat capacity that
deals in grams

• Molar heat does enable us to make one interesting
  observation

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Dulong-Petit Law is approximately true it says
that it takes 25 Joules to raise 1 mole of atoms
1degree K
Specific Heat x molar mass 25jmol C
Molar heat capacity for Ag is 25.3 Molar
heat capacity for Al is 24.2 Molar heat
capacity for NaCl is 50.5 Molar heat
capacity for BaCl2 is 75.1
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Heat transference is dependent on three factors

• a)     THE CAPACITY OF A SUBSTANCE TO ABSORB HEAT
• b)    THE MASS OF THE SUBSTANCE
• c)     THE CHANGE OF THE TEMPERATURE OF THE MASS

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To see how the temperature of an object will
change with applied heat you use the equation

• q s m ?T

q is the heat transferred in calories  s is the
specific heat in CALORIES  m is the mass in
grams  ?T is the temperature in Co    
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How much energy is required to heat a nail with a
mass of 7 g from 25 C until it becomes red hot
at 750 degrees the specific heat of iron is .45
J/gCo
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If 5750 J of energy are added to a 455g piece of
24Co granite (sg of .8) what is the final
temperature of the granite
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30 g sample of a unknown metal is heated form 22
C to 59.2 during the process 1000 joules of
heat is absorbed by the metal. What is the
specific heat of the metal
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• Using our nifty equation no matter what the
  substance just insert the number of joules of
  heat that enters a system plug in the mass of the
  substance and its specific gravity whippo sappo
  we find the new and altered temperature.