- According to the kinetic theory of matter, all matter is
made up of tiny particles – called atoms or molecules.
- These particles are always moving, and it is this
movement that helps decide what state of matter exists
(solid, liquid, gas, plasma).
- The particles have potential and kinetic energy (kinetic as
they are moving, and potential as they are potentially
attracted or repulsed by each other).
- The TOTAL of all these forms of energy in a particular
substance is called its thermal energy. (Physicists also call
this internal energy because it is internal to a substance).
- When you strike a nail with a
hammer, it becomes warm. Why?
When you put a flame to a liquid,
the liquid becomes warmer as its
molecules move faster. Why?
- In both the above examples, the molecules are made to
race back and forth faster. In other words, they gain kinetic
energy. In general, the warmer an object, the more kinetic
energy its atoms and molecules possess.
- Temperature, the degree of “hotness” or “coldness” of
an object, is proportional to the average (NOT total) kinetic
energy of the atoms or molecules making it up.
- Temperature is expressed quantitatively by a number that
corresponds to the degree of hotness on some chosen scale.
- The scale most often used
world-wide is the Celsius
thermometer, where a zero
(0) is assigned to the
temperature at which water
freezes, and 100 is assigned
to the temperature at which
water boils (at standard
- In the U.S., the number 32 is traditionally assigned to
the temperature at which water freezes, and the number
212 is the temperature at which water boils. This
thermometer is called the Fahrenheit scale.
Upper Limits of Temperature
- In principle, there is no upper limit to
-As thermal motion increases, a solid object first melts
than vaporizes. As the temperature is further increased,
molecules dissociate into atoms, and atoms lose some of
their electrons, thereby creating a cloud of electrically
charged particles – called plasma.
- Plasmas exist in stars, where the temperature is many
millions of degrees Celsius.
Lower Limits of Temperature
- In contrast to high temperatures, there is a definite limit at
the opposite end of the scale, called absolute zero.
- Temperature is based upon
kinetic energy of molecules.
The colder something is, the
slower the molecules.
Eventually, the molecules
will slow down SO much,
they will essentially stop
moving (they will be out of
energy, and so they can’t get
- The absolute temperature scale is called the Kelvin scale.
Absolute zero is 0 K. The melting point of ice is 273 K, and
the boiling point of water is 373 K. There are no negative
numbers on the Kelvin scale.
- Here’s the part you all LOVE to hate: How to convert
from one scale to the other.
Fahrenheit to Celsius
Celsius to Fahrenheit
Celsius to Kelvin
Kelvin to Celsius
-We know that temperature is the hot or cold nature of
something (based on the kinetic energy of its molecules), so
what is heat? Heat is the thermal energy transferred from
one thing to another due to a temperature difference.
- If you touch a hot stove,
thermal energy enters your hand
because the stove is warmer than
your hand. When you touch a
piece of ice, thermal energy
passes out of your hand and into
the colder ice.
-The direction of energy flow is ALWAYS from a
warmer thing to a neighboring cooler thing. (This is
a basic concept of meteorology and thermodynamics –
things always go from high to low pressure, and from
hot to cold temperatures until equilibrium is reached).
Transfer of Heat Energy
- According to the previous definition, matter does not
contain heat. Matter contains thermal energy (NOT heat!).
- Heat is the thermal
energy transferred from
one thing to another due
to a temperature
difference. Once thermal
energy has been
transferred to an object
or substance, it ceases to
be heat. Heat is simply
thermal energy in
- So, does that mean a cold
substance contains something
opposite from thermal energy? No.
It just lacks thermal energy. When
outdoors on a winter day, you feel
chilly not because something
called “cold” gets to you, but
because you lose body heat (hot to
cold, remember?). That’s the
purpose of your coat – to slow the
heat flow from your body to the
surrounding air. Cold is just
reduced thermal energy.
Heat Versus Cold
Making Sense So Far?
Question: Suppose you apply a flame to 1 liter of water for a
certain time and its temperature rises by 2°C. If you apply the
same flame for the same time to 2 liters of water, by how
much will its temperature rise?
Answer: Its temperature will rise by only 1°C, because there
are twice as many molecules in 2 liters of water, and each
molecule receives only half as much energy on the average.
So, the average kinetic energy, and thus the temperature,
increases by half as much.
- Heat is a form of energy, and it is measured in joules. It
takes about 4.2 joules of heat to change 1 gram of water by 1
- A unit of heat common in
the U.S. is the calorie, which
is defined as the amount of
heat energy needed to
change the temperature of 1
gram of water by 1 Celsius
degree (the relationship
between calories and joules
is that 1 calorie = 4.18
- The energy ratings of
foods are measured by the
energy released when they
are burned. The heat unit
for labeling food is the
kilocalorie, which is 1,000
calories. But we don’t use
this term. For clarity, the
food unit is usually called a
Calorie, with a capital C.
So, 1 Calorie is really
Counting Food Calories
• Calories in Physics and in food:
– In Physics: 1 calories is the amount of energy needed to raise the
temperature of 1 g of water 1 C.
– In food: 1 Calories is the amount of energy needed to raise the
temperature of 1 kg water 1 C
1 Cal =1,000 cal
• Normal body maintenance uses up about 15 calories per day for
each pound of body weight.
• You must consume about 3500 calories to gain a pound of weight.
• To burn off 500 calories you would have to run 5 miles, bike 15
miles, or swim for an hour.
Specific Heat Capacity
-While eating, you’ve likely noticed that some foods remain
hotter much longer than others. Whereas the filling of hot
apple pie can burn your tongue, the crust does not.
-Different substances have different capacities for storing
thermal energy. A gram of water requires 1 calorie of
energy to raise the temperature 1 degree Celsius. It takes
only about one-eighth as much energy to raise the
temperature of a gram of iron by the same amount.
-Water absorbs more heat than iron for the same change in
temperature. We say water has a higher specific heat
capacity (sometimes called specific heat).
Specific Heat Capacity
Water’s high specific heat capacity changes the world’s
climate. The Gulf Stream retains heat as it moves northward
from the Caribbean, ultimately causing Northern Europe to
have a warmer climate than Canada, even though they are near
the same latitude.
- We can use specific heat capacity to write a formula for the
quantity of heat Q involved when a mass m of a substance
undergoes a change in temperature:
Q = mcΔT
In other words, heat transferred to or from an object =
specific heat capacity of the object x mass of the object x its
- This equation is valid for a substance that gets warmer as
well as for one that cools. When a substance is warming up,
the heat transferred into it, Q, is positive. When a substance
is cooling off, Q has a minus sign.
Q = mcΔT
A 2.0-kg aluminum pan is heated on the stove
from 20°C to 110°C. How much heat had to be
transferred to the aluminum? The specific heat
capacity of aluminum is 900 J/kg°C.
Q = (2.0 kg) (900 J/kg°C ) (110°C - 20°C)
Q = 162,000 J
Q = 1.62 x 105
• How much heat is required to raise the
temperature of 70g of water from 20 o
Phase Change and Latent Heat
• When an object goes through a change of phase or
state, heat is added or removed without changing the
temperature. Instead, the state of matter changes:
solid to liquid, for example.
• The amount of heat needed per unit mass to produce
a phase change is called the latent heat (L)
– The latent heat of fusion of water is 80 cal/g (Lf
= 80 cal/g is 80 cal/g): it takes 80 calorie of heat
the melt 1 g of ice at 0C to become water at 0C.
– The latent heat of vaporization of water is 540
cal/g (Lv = 540 cal/g): it takes 540 calories of
heat to turn one gram of water at 100 C into
steam at 100 C.
Changes in State
• Heat of Fusion (Hf)
– Conversion from Solid Liquid
• Heat of Vaporization (Hv)
– Conversion from Liquid Gas
Formula Q = m Hf or m Hv
Hf = 80 cal/g or 334 J/g (for ice)
Hv = 540 cal/g or 2260 J/g (for steam)
If the specific heat capacity of ice is
0.5 cal/g⋅C°, how much heat would have
to be added to 200 g of ice, initially at
a temperature of -10°C, to
(a) raise the ice to the melting point?
(b) complete melt the ice?
Example Box 10.1
Change in State Graph
Change in State
0 10 20 30 40
Time ( Min )
1. Copy this graph1. Copy this graph
2. Identify specific heat, heat of fusion, and heat of2. Identify specific heat, heat of fusion, and heat of