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Notes on. Heat Energy. Energy . Is the capacity to do work or to produce heat Forms: Kinetic energy = energy of motion Potential energy = energy of position Thermal energy = a form of KE caused by random internal motion of particles of matter. Heat. A form of energy

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Notes on

Notes on

Heat Energy


Energy
Energy

  • Is thecapacity to do workor to produce heat

  • Forms:

  • Kinetic energy= energy of motion

  • Potential energy= energy of position

  • Thermal energy= a form of KE caused by random internal motion of particles of matter


Heat

  • A form ofenergy

  • Is measured in calories (cal) orJoules(J)

  • 1 cal =4.184 J

  • 1 Cal = 1000 cal

  • Isnotthe same as temperature!


Temperature
Temperature

  • A measure of theKinetic Energyin a system

  • Units are:FahrenheitorCelsius(Centigrade) orKelvin


Absolute zero
Absolute Zero

  • Corresponds to about-273 oC

  • Is the (theoretical) point at which the motion of particles of matter –their kinetic energy- ceases


More about temperature
More about Temperature

  • For most applications in Chemistry, we will use theCelsiusscale.

  • There is at least one topic for which we must change our temperature units to Kelvins – that is forGas Laws.

  • On the Kelvin scale there is no “zero” and no negative values. That becomes important in calculations involving gases, since a negative temp might make it look like, in calculations, that there is a negative volume.


Law of conservation of energy
Law of Conservation of Energy

Energy is neither created nor destroyed…it just

Changes form.

By the way…

We can record a reading as, for example, 102.3 degrees Celsius -

but - if we were to record a temperature using the Kelvin scale, we would simply state, for example, “275 Kelvins” (not“degrees kelvin”)


Conversions
Conversions

  • C = K – 273so thereforeK = C + 273

  • C = 5/9 (F – 32) and F = (9/5*C) + 32

22.5oC = ___ K

55oF = ___ oC

290 K = ___oC

97 oF = ___ oC

Temperature “Sense” – Memorize these:

Room Temp in C: 22

Body Temp in C: 37

Boiling Pt/Freezing Pt: 100/0


Specific heat
Specific Heat

  • A property of matter that is unique to each element or compound –

  • It does not depend on the amount of matter present, so is anintensiveproperty

  • Also called “heat capacity”

  • “the amount of energy needed to raise the temperature of 1 g of a substance by 1 degree Celsius”


Formula for specific heat
Formula for Specific Heat

  • Q = mcDT

  • WhereQ= “heat” and is measured in J

  • Wherem= mass and is measured in g

  • Wherec= specific heat and is measured in …(see next slide!)

  • WhereDT= (“delta T”) is “change in temperature” and is measured in C


Unit for specific heat
Unit for Specific Heat

  • So what is the unit for “c”?

  • Let’s rearrange the formulaQ = mcDTin terms of c (we call this “deriving”)

  • c = Q / mDT

  • All units in Chemistry and Physics come from the formulas that they’re in

  • Therefore,c = Q / mDT

J

/

g

oC


Specific heat of water
Specific Heat of Water

  • Water, H2O, has anextremely high“heat capacity”, which in plain language, means that it takes a lot of energy to heat it up and it has a tremendous ability to retain heat (aka: takes a lot to cool it down)

  • The specific heat of water is 4.18 J/goC(which you may recognize as 1 calorie)

  • Memorize this!!!!!!!!!!!


Why that s important
Why That’s Important

  • It affects your life every day.

  • The reason it tends to be cooler at the ocean than in the valley is due to the cH2O

  • The reason that hurricanes get stronger over warm water is that they’re deriving their energy from the heat contained in the water (maybe that doesn’t affect you every day); it gives them energy

  • The reason a steam burn is worse than a regular burn is due to the energy in the steam

  • Can you think of other examples?


Reminder law of conservation of energy
Reminder: Law of Conservation of Energy

  • We know that energy cannot be created or destroyed

  • We know that heat is a form of energy

  • So…it must be true that the heat lost by one substance must be “accountable” by another substance or substances, or…

  • Q lost = Q gained


If q lost q gained
If Qlost = Qgained

  • …andif Q = mcDT, then it must be true that…

  • (mcDT) lost = (mcDT) gained

  • And that’s the foundation for our next lab: “Specific Heat of a Metal”


Pre lab specific heat of a metal
Pre-Lab: Specific Heat of a Metal

  • Discussion: You will be given a sample of a metal. You will have to determine its specific heat.

  • We already know the specific heat of water (4.18 J/goC)

  • We will use the concept of …

  • (mcDT)lost =(mcDT)gainedto solve for the unknown c for the metal


Lab specific heat of a metal
Lab: Specific Heat of a Metal

  • (mcDT)gained = (mcDT)lost

  • (mcDT)gained by water = (mcDT)lost by metal

  • (mcDT)water = (mcDT)metal

If the metal

starts at the

boiling point

of water, that’s

your T1.

The temp after the

water has stopped

rising has to be

the temp of the

metal as well, so

that is T2.

Measure

the mass

of the

water

Measure the

initial temp of the

water before the metal was added; the final temp after

the metal heats it up

You will be

calculating

the “c” for

the metal

You know

the “c”

for

water

(4.18 J/gC)

Measure the mass of the metal


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