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Physics - Chp 7 - Temperature, Energy and Matter
Transcript of Physics - Chp 7 - Temperature, Energy and Matter
Heat? 7.4 Heat
Made of Particles
In Motion Elements
of Matter Atoms
Smallest Particles Compounds The idea of
atoms Albert Einstein (in 1905)
proposed that Brownian motion is caused by collisions between visible particles and smaller, invisible partiles. Democritus 430 BC Ancient Chinese ideas -(551-479 BC)
metal, wood, water, fire, earth make up matter.
Ancient Indian ideas - 6th century BC
earth, water, fire, air, and ether
Ancient Greek ideas - 495-435 BC
fire, water, air, and earth
Similar ideas about matter
basic building blocks What are
elements? pure substance that cannot be
broken down intosimpler substances
by physical or chemical means smallest particle of an element that retains the chemical identity of the element Each element has a unique type of atom.
All atoms of a given element are similar to each other contains two or more different elements
chemically joined and that has the same
composition throughout Molecules -
contains two or more different elements chemically joined and that has the same composition throughout mixture
contains more than one kind of atom, molecule, or compound 7.1
Review Explain why Brownian
motion provides evidence
for the existence of atoms
and molecules. Describe the difference
and give an example between elements,
mixtures. Pollen grains being pushed around by the
molecules within the water itself –
in other words, they were being “jostled”
about by the atoms. Although Brown
himself did not provide such an explanation
for this phenomenon, it is still named in his honor,
and at least provides a framework for later work on
proving the existence of atoms. Measuring
Temperature Thermometers What is
Temperature Phases of
Zero Show PPT All thermometers are based on a physical property (such as color or volume) that changes with temperature. measure of the kinetic energy
of individual atoms atoms are in constant motion.
Temperature measures the KE in just the random motion. throwing a rock does not make it hotter
When you heat a rock with a torch,
each atom jiggles back and forth w/
but the whole rock stays in same place solid
holds its shape and
does not flow.
molecules vibrate in
place, but on average,
don’t move far from
their places. Liquid
holds its volume, but does
not hold its shape
molecules in a liquid are about as
close together as a solid,
have enough energy to exchange
positions with neighbors.
Liquids flow because molecules
can move around. gas
flows like a liquid, can expand
contract to fill a container.
A gas does not hold its volume.
molecules have enough energy
to completely break away
much farther apart than liquid/solid. Intermolecular forces
molecules are attracted to each other by these forces
strength of forces determines whether matter exists as a solid, liquid, or gas
KE from temperature tends to push molecules apart. As the temperature changes,
balance between temperature & intermolecular forces changes.
At temperatures below 0°C,
the intermolecular forces in water are strong enough to overcome temperature and water becomes solid (ice). melting point
temperature at which a substance changes from a solid to a liquid.
different melting points.
intermolecular forces between particles in each substance vary in their strength.
Stronger intermolecular forces require more energy to break. Boiling
enough energy added, the intermolecular forces are completely pulled apart
liquid becomes a gas.
Boiling takes place as bubbles of gas particles form and rise to the surface. Evaporation
I when molecules go from liquid to gas at temperatures below the boiling point.
happens because temperature measures the average random kinetic energy of molecules.
takes energy away from a liquid. Changes in state
require energy limit to how cold matter can get.
As temperature reduces, molecules move more and more slowly.
When temperature = absolute zero,
molecules have lowest energy
temperature cannot get any lower Kelvin scale
starts at absolute zero
energy of atoms
Add 273 to Celsius Plasma
temperatures >10,000 °C
atoms in a gas start to break apart.
matter becomes ionized as electrons
are broken loose from atoms.
electrons are free to move independently,
so plasma can conduct electricity.
example: Lightning and the sun. higher the temperature,
- higher the random KE of each atom
heat a rock with a torch long enough,
- atoms get a lot of energy & break from each other.
- The rock melts.
If you keep heating the liquid rock will start to boil.
- In boiling some atoms have so much energy they
leave & fly off into the atmosphere. 7.2
Review In which system are the molecules moving faster, a cold glass of tea or a hot cup of tea? Describe what happens at the atomic level during melting. Explain why particles in a gas are free to move far away from each other. hot tea-
more KE energy melting point is the temperature at which a substance changes from a
solidto a liquid.
the particles have enough energy to break the intermolecular forces between particles apart. The molecules in a
gas have enough energy to completely break away from each other Heat,
Thermal Energy Units of Heat
Thermal Energy Specific Heat Calculating Energy
Changes from Heat Why is
Different? Thermal energy
sum of KE of atoms or molecules added up together. flow of thermal
energy depends on
amount of matter
you have. heat flows
when a difference in temperature.
Heat flows naturally from the warmer object (higher energy) to the cooler one (lower energy). The joule
metric unit for measuring heat
calorie = 4 joules
quantity of heat needed to increase temperature of 1 gram of water by 1 degree Celsius.
nutritional calore - 1000 calories = C
quantity of heat it takes to increase temperature of 1 pound of water by 1 degree Fahrenheit. Why so many units? how much heat is needed to raise the
temperature of one kilogram of a
material by one degree Celsius. If you add heat to an object, how much will its temperature increase?
the mass of the object
kind of material you are heating Knowing the specific heat tells you how quickly the temperature of a material will change as it gains or loses energy specific heat is low (like steel),
then temperature will change quickly
each degree of change takes less energy.
specific heat is high (like water),
temperature will change relatively slowly Hot apple pie filling stays hot
( large specific heat)
because it is mostly water.
Pie crust =lower specific heat
cools much more rapidly. How much heat is needed to raise the temperature of a 250-liter hot tub from 20°C to 40°C? The specific heat of water is 4,184 J/kg°C. (HINT: 1 liter of water has a mass of 1 kilogram.)
:E = m C(p) (T2 – T1)
E = (250L × 1kg/L) × 4,184 J/kg°C (40°C - 20°C)
= 20,920,000 joules. How much heat energy is needed to raise the temperature of 2.0 kilograms of concrete from 10°C to 30°C?
The specific heat of concrete is 880 J/kg°C. How much heat energy is needed to raise the temperature of 2.0 kilograms of concrete from 10°C to 30°C? The specific heat of concrete is 880 J/kg°C.
Relationships: E = m C(p)(T2 – T1)
E = (2.0 kg) × 880 J/kg°C (30°C - 10°C)
= 35,200 joules How much heat energy is needed to raise the temperature of 5.0 grams of gold from 20°C to 200°C?
The specific heat of
gold is 129 J/kg°C. How much heat energy is needed to raise the temperature of 5.0 grams of gold from 20°C to 200°C? The specific heat of gold is 129 J/kg°C.
First - convert 5.0 g ------- = 0.005 kg
Relationships: E = m C(p)(T2 – T1)
E = (0.005 kg) × 129 J/kg°C (200°C - 20°C)
= 116.1 joules materials made up of heavy atoms/molecules have low specific heat
Heavy particles mean fewer per kilogram.
Energy that is divided between fewer particles means more energy per particle, and therefore more temperature change Water
high specific heat
Water covers 75% of Earth
helps regulate the temperature.
day = oceans keep Earth cool,
night = they keep Earth warm
- slow rate at which heat is
emitted back into space.
Land, low specific heat,
experiences large changes 7.3
Review What is the difference between temperature and thermal energy? What conditions are necessary for heat to flow? How much heat energy is required to raise the temperature of 20 kilograms of water from 0 degrees C to 35degrees C? How much heat energy is required to raise the temperature of 20 kilograms of water from 0 degrees C to 35 degrees C?
Relationships: E = m C(p)(T2 – T1)
E = (20 kg) × 4,184 J/kg°C (35°C - 0°C)
= 2,928,800 joules heat flows any time there is a
difference in temperature. Temperature
measure of the kinetic energy of individual atoms
sum of all the kinetic energy of the atoms or molecules added up together. Heat Conduction Thermal Conductors
Insulators Convection Thermal
Radiation Rate of
Heat Transfer Thermal energy flows from a material at a higher temp. to a material at lower temp. transfer of heat by the direct contact of particles of matter occurs between two materials at different temperatures and when they are
touching each other Conduction works through
between molecules. Thermal equilibrium occurs
when two bodies have the same temperature.
No heat flows because the temperatures are the same. Materials that conduct heat easily conduct heat poorly Conduction - happens solids, liquids, gases.
Solids is best -particles packed close.
gas - particles spread so far apart,
relatively few collisions occur, Conduction happens
if there are particles
available to collide
with one another.
cannot occur in the
vacuum of space. transfer of heat through the motion of fluids (air/water) natural convection
Fluids expand when they heat up.
expansion increases the volume, but mass,
warm fluid has lower density than surrounding cooler fluid.
warmer fluid floats to the top
cooler fluid sinks to the bottom. forced convection
in houses a boiler heats water
pumps circulate the water to rooms.
heat is being carried by a moving fluid natural and forced convection often occur at the same time. electromagnetic waves (including light)
produced by objects b/c of temp.
Objects above absolute zero
emit thermal radiation. comes from energy of atoms.
The power in thermal radiation increases with higher temperatures b/c energy of atoms increases w/ temp Some surfaces absorb more energy
Black surfaces absorb almost all radiation that falls on them.
silver mirror surface reflects most radiation, absorbing little can travel through space
carried by electromagnetic waves
does not require matter to provide a path for heat flow.
travels fast — at the speed of light. heat transfer always occurs from hot to cold until thermal equilibrium is reached.
humans regulate temperature through constant flow of heat Humans are most comfortable
when the air temp. about 75°F
because the rate of heat flow out of
the body matches the rate at which
the body generates heat internally. 7.4
Review Name one ex. of heat transfer through conduction. What is the primary type of heat transfer that occurs between a hot and cold fluid when they are mixed together? Which object would you expect to emit more thermal radiation, a lamp that is turned on, or a rock at room temperature. Explain your answer. In which direction will heat flow between an ice cube and the air on the room? Explain your answer. spoon in
hot cocoa conduction the lamp - power in thermal radiation increases with higher temperatures because the thermal
energy of atoms increases with temperature Thermal energy flows from a higher temperature to a a lower temp. Assuming the room is at room temp, it will flow from the room to the ice cube. http://www.cpo.com/home/ForStudents/PhysicsAFirstCourse/tabid/238/default.aspx?MediaFileId=3000 Show PPT on History
of Temperature HW - Worksheet on
Specific Heat Problems Complete