Transcript 16.1 Thermal Energy and Matter

16.1 Thermal Energy and Matter
Count Rumford
supervised the drilling of
brass cannons in a
factory in Bavaria.
From his observations,
Rumford concluded that
heat is not a form of
matter.
16.1 Thermal Energy and Matter
Work and Heat
Heat is the transfer of thermal energy from one
object to another because of a temperature
difference.
Heat flows spontaneously from hot objects
to cold objects.
16.1 Thermal Energy and Matter
Work and Heat
A drill is a machine that does work on the
cannon. Remember that no machine is 100%
efficient. Some of the work done by the drill is
useful, but some energy is lost due to friction.
Heat flows from the cannon to a surrounding
water bath because the cannon is at a higher
temperature than the water.
16.1 Thermal Energy and Matter
Temperature
What is the temperature of an object related
to?
Temperature is related to the average kinetic
energy of the particles in an object due to
their random motions through space.
16.1 Thermal Energy and Matter
Temperature
Temperature is a measure of how hot or cold
an object is compared to a reference point.
• On the Celsius scale, water freezes at 0°C and
boils at 100°C.
• On the Kelvin scale, absolute zero is the
temperature where all molecular motion stops. It
is defined as a temperature of 0 Kelvins.
16.1 Thermal Energy and Matter
Temperature
• How does heat flow from a high to a low
temperature?
– It does this through collisions.
– On average, high energy particles lose energy and low
energy particles gain energy in collisions.
– So overall, collisions transfer thermal energy from hot to
cold objects.
16.1 Thermal Energy and Matter
Thermal Energy
What is thermal energy?
Thermal energy is the total potential and kinetic
energy of all the particles in an object.
Thermal energy depends on the mass,
temperature, and phase (solid, liquid, or gas)
of an object.
16.1 Thermal Energy and Matter
Thermal Energy
• Thermal energy depends on mass.
– A cup full of tea and a pitcher full of tea have the same
temperature.
– However, because the pitcher holds a larger amount, or
mass, of tea, it also has more particles than the cup.
– Because it has more particles it can be said that it has
more thermal energy
16.1 Thermal Energy and Matter
Thermal Energy
• Thermal energy depends on temperature.
– If you have a cup of hot tea and a cup of cold tea, they
both contain the same number of particles and have the
same mass.
– Because the particles in warmer objects move faster than
the particles in colder objects, there are more collisions
taking place in the warm cup of tea.
– Because the particles are moving faster, the average
kinetic energy is greater and thus it contains more thermal
energy.
16.1 Thermal Energy and Matter
Thermal Energy
Thermal energy depends on mass and temperature.
A. The tea is at a higher temperature than the
lemonade.
B. The lemonade has more thermal energy because
it has many more particles.
16.1 Thermal Energy and Matter
Thermal Contraction and Expansion
What is thermal expansion?
Thermal expansion is an increase in the
volume of a material due to a temperature
increase.
Thermal expansion occurs when particles of
matter move farther apart as temperature
increases.
16.1 Thermal Energy and Matter
Thermal Energy
If you take a balloon outside on a cold winter
day, it shrinks in a process of thermal
contraction.
• As temperature decreases, the particles that
make up the air inside the balloon move more
slowly, on average.
• Slower particles collide less often and exert less
force.
• Gas pressure decreases and the balloon
contracts.
16.1 Thermal Energy and Matter
Thermal Energy
If you bring the balloon inside, it expands.
Gases expand more than liquids and liquids
usually expand more than solids.
16.1 Thermal Energy and Matter
Thermal Energy
As temperature increases, the alcohol in a
thermometer expands, and its height increases
in proportion to the increase in temperature.
In an oven thermometer, strips of steel and
brass expand at different rates as the coil
heats up. The coil unwinds, moving the needle
on the temperature scale.
16.1 Thermal Energy and Matter
Specific Heat
What is specific heat?
Specific heat is the amount of heat needed to
raise the temperature of one gram of a material
by one degree Celsius.
The lower a material’s specific heat, the
more its temperature rises when a given
amount of energy is absorbed by a given
mass.
16.1 Thermal Energy and Matter
Specific Heat
When a car is heated by the sun, the
temperature of the metal door increases more
than the temperature of the plastic bumper.
The iron in the door has a lower specific heat
than the plastic in the bumper.
16.1 Thermal Energy and Matter
Specific Heat
16.1 Thermal Energy and Matter
Specific Heat
In this formula, heat is in joules, mass is in
grams, specific heat is in J/g•°C, and the
temperature change is in degrees Celsius.
16.1 Thermal Energy and Matter
Specific Heat
What is a calorimeter?
A calorimeter is an instrument used to measure
changes in thermal energy.
It uses the principle that heat flows from hotter
to colder objects until they both reach the same
temperature.
The thermal energy released by one object is
equal to the thermal energy absorbed by
another object.
16.1 Thermal Energy and Matter
Specific Heat
A calorimeter is used to
measure specific heat. A
sample is heated and
placed in the calorimeter.
The temperature change is
observed.
16.1 Thermal Energy and Matter
Assessment Questions
1. What is the thermal energy of an object?
a.
b.
c.
d.
the total number of atoms or molecules
the total kinetic energy of the atoms or molecules
the average kinetic energy of the atoms or molecules
the average mechanical energy of the atoms or
molecules
16.1 Thermal Energy and Matter
Assessment Questions
1. What is the thermal energy of an object?
a.
b.
c.
d.
the total number of atoms or molecules
the total kinetic energy of the atoms or molecules
the average kinetic energy of the atoms or molecules
the average mechanical energy of the atoms or
molecules
ANS: B
16.1 Thermal Energy and Matter
Assessment Questions
2. What causes a gas to expand when its
temperature is increased?
a. The number of particles increases as temperature
increases.
b. Each particle expands as its temperature increases, so
the total volume increases.
c. As temperature increases, more electrons leave atoms
and move separately.
d. As gas particles move faster, they overcome some
forces of attraction.
16.1 Thermal Energy and Matter
Assessment Questions
2. What causes a gas to expand when its
temperature is increased?
a. The number of particles increases as temperature
increases.
b. Each particle expands as its temperature increases, so
the total volume increases.
c. As temperature increases, more electrons leave atoms
and move separately.
d. As gas particles move faster, they overcome some
forces of attraction.
ANS: D
16.1 Thermal Energy and Matter
Assessment Questions
3. The specific heat of water is 4.18 J/g•°C. How
much heat is required to raise the temperature of
1,000 grams of water by 50°C?
a.
b.
c.
d.
83.6 J
83.6 kJ
209 J
209 kJ
16.1 Thermal Energy and Matter
Assessment Questions
3. The specific heat of water is 4.18 J/g•°C. How
much heat is required to raise the temperature of
1,000 grams of water by 50°C?
a.
b.
c.
d.
83.6 J
83.6 kJ
209 J
209 kJ
ANS: D
16.1 Thermal Energy and Matter
Assessment Questions
4. What property of matter can be measured using a
calorimeter?
a.
b.
c.
d.
temperature
thermal expansion
specific heat
mass
16.1 Thermal Energy and Matter
Assessment Questions
4. What property of matter can be measured using a
calorimeter?
a.
b.
c.
d.
temperature
thermal expansion
specific heat
mass
ANS: C
16.1 Thermal Energy and Matter
Assessment Questions
1. Temperature is the transfer of thermal energy
from one object to another.
True
False
16.1 Thermal Energy and Matter
Assessment Questions
1. Temperature is the transfer of thermal energy
from one object to another.
True
False
ANS:
F, Heat