**The internal energy or thermal energy of
a substance is determined by the movement of the molecules and
the potential energy of the arrangement of molecules.**

**Temperature is the measure of the
average kinetic energy of the
molecules.**

**Heat energy is the energy transferred
from a warmer substance to a
colder one by the collisions of
molecules.
The unit for all energy is the joule. However, sometimes the calorie
is used for heat. The calorie is defined as the amount of heat
needed to raise 1 g of a substance 1 degree Celsius.
1 cal = 4.18 joules or 1kcal = 4180 J
To convert calories to joules
multiply the calories by
4.18.
To convert joules to calories
divide by 4.18.**

Temperature is measured by the

changes it causes in matter like

expansion. A thermometer is one of

the instruments used. A

thermocouple is another.

**There are two temperature scales
used in the SI.
1. Celsius scales sets zero at the
freezing point of water and 100 at
boiling.**

**2. Kelvin scale (sometimes called
the absolute scale) sets 0 at
absolute zero the point at which a
substance has no kinetic energy.
The freezing point of water is 273 on
this scale and boiling is 373.**

**The Fahrenheit scale is the scale
commonly used in the English
system. It sets freezing at 32 and
boiling at 212.**

Heat Transfer

**1. Conduction - heat transferred by
contact.
Example: metal spoon gets hot in a
pot of boiling water**

**2. Convection - heat transferred by
the movement of fluids (gases and
liquids)
Example: hot air rises in a room.**

**3. Radiation - heat transferred by
waves (infrared) no material is
needed.
Example: heat reaches earth from
the sun.**

**Heat transfer will stop when thermal equilibrium
is reached, that is the rate at which energy flows out of a substance
equals the rate that energy flows into the substance.
Calculating Heat**

**Specific heat is the amount of heat
needed to raise the temperature of
1kg of a substance 1 degree.**

**m - is mass in kg
c - is the specific heat of the material
DT
- change in temperature**

**According to the law of conservation of
energy, energy cannot be created or destroyed. This is also true
of heat energy.**

**If a substance gets hotter something else
must get colder.**

**For example: 200 g of water at 80 degreesC
is mixed with 200 g of water at 10 degree C. What is the final
temperature?**

**The 80 degree water will lose heat and the
10 degree water will gain heat. They will eventually come to thermal
equilibrium and be at the same temperature.**

**Matter occurs commonly in 3 phases. When
a phase change occurs heat is needed to rearrange the molecules.
This heat does not change the kinetic energy
so the temperature does not change.
during a phase change.**

**The boiling point is the temperature
at which vaporization/condensation
occurs.
The heat needed to vaporize or condense a substance is called
the Heat of Vaporization.
The heat of vaporization is the
amount of heat need to vaporize or
condense 1 g or kg of a substance.
The heat of vaporization of water is
540cal/g or 2.26 x 10^6 J/kg. This means for every g of water
that evaporates 540 cal of heat must be absorbed.
For every g of water vapor that
condenses to liquid water 540 cal
must be lost.**

**To calculate the heat needed to make
this phase change Use the following
equation: Q = mHV**

**Q= energy
m = mass
HV = heat of vaporization**

**Example: How much heat would it take to
change 3 kg of water at 100 degrees C to steam?**

**The freezing point of a substance is
the temperature at which freezing/
melting occurs.
The amount of heat that must be
removed for a liquid to freeze or
added for a solid to melt is called the
Heat of Fusion.
The Heat of Fusion is the amount
of heat necessary to freeze/melt 1 g or kg
of a substance.
The heat of fusion of water is 80
cal/g or 3.34 x 10^5 J/kg**

**To calculate the amount of heat
involved in freezing or melting use
the following equation:
Q = mHF**

**Q = heat energy
m = mass
HF = heat of fusion**

**Example: How much heat would it take to
melt .5 kg of ice at 0 degrees C?**

**Before a substance can change phase it must
reach its freezing/melting or boiling/condensing point. The heat
needed to reach this point is determined by the temperature change
equation:**

**The latent heat to change phase is next
calculated by using the equation for the phase change:**

**The heats are then added together to find
the total heat.**

**Example how much heat will it take to turn
2 kg of water at 30 degrees celsius to steam?**

**First you must calculate how much heat it
will take to change the temperature of the water from 30 to 100
degrees C and then how much heat it will take to change the water
to steam.**

**Q = mcDTH2O
+ mHf**

**Q = (2kg) (4180 J/kg*C)(100-30 C)**

**Q = 585,200 J + 4,520,000 J**

**Q = 5,110,000 J**

**Thermal energy can be increased either by
adding heat or by doing work ona system.**

**DQ
= Work + Additional Heat**

**1ST Law of Thermodynamics -the total increase
in the thermal energy of a system is the sume of the work done
on it and the heat added to it,**

**This is just a restatment to the Law of
Conservation of Energy.**

**The converison of mechanical energy to thermal
energy (rubbing your hands together) is easy. The reverse process,
conversion of thermal to mechanical energy is more difficult.**

**Heat engines are devices able to convert
thermal energy to mechanical.**

**Example: A 4.2 g lead bullet moving at 275
m/s steel plate and stops. If all its kinetic energy is converted
to thermal energy and none leaves the bullet, what is its temperature
change?**

**KE = 1/2 mv^2**

**Q = mcDT**

**If all the kinetic energy is converted then:
KE = Q**

**1/2mv^2 = mcDT**

**1/2(.0042kg)(275m/s)^2 = (.0042kg)(130J/kg-C)DT**

**75625 = 130DT**

**290 degrees = DT**

**2ND Law of Thermodynamics -natural processes
go in a direction that increases the total entropy of the universe**

**Entropy is defined as disorder.**