Thermal Physics (3)

This abstract topic connects the atomic world to the observable world. For example,

why do tires need to have air pumped in them as winter is arriving?

Mr. KlapholzShaker Heights

High School

Particle Basics

• Particles can be _ _ _ _ _.• Particles can be molecules (example: H2O)• Atoms are _ _ _ _ _ _ _ than we can imagine.• Overhead transparencies on the mole.

Particle Basics

• Particles can be atoms.• Particles can be molecules (example: H2O)• Atoms are _ _ _ _ _ _ _ than we can imagine.• Overhead transparencies on the mole.

Particle Basics

• Particles can be atoms.• Particles can be molecules (example: H2O)• Atoms are smaller than we can imagine.• Overhead transparencies on the mole.

Temperature (T)

• Although you already know the basics of temperature, there are some fine points.

• The faster the particles, the higher the temperature. But temperature is not proportional to the average speed of the particles.

• Temperature is proportional to the square of the average speed of the particles. Temperature is proportional to the kinetic energy of the particles. (1/2)mv2 = (3/2)kT

Temperature

• The coldest temperature is where no motion occurs: T = -273 Centigrade = 0 _ _ _ _ _ _ _.

• When two objects are put in ‘thermal contact’ then the colder one will always warm up, and the warmer one will always cool down.

Temperature

• The coldest temperature is where no motion occurs: T = -273 Centigrade = 0 Kelvins.

• When two objects are put in ‘thermal contact’ then the colder one will always warm up, and the warmer one will always cool down.

Heat (Q)

• Heat is energy that is transferred from one body to another as a result of difference in temperature.

Internal Energy (U)

• A large cool pool of water has _ _ _ _ internal energy than a hot fork.

• Internal energy comes from two parts: (1) kinetic (related to temperature) and potential (related to the forces between particles).

• If everything else is equal, then the bigger the object, the more internal energy it has.

Internal Energy (U)

• A large cool pool of water has more internal energy than a hot fork.

• Internal energy comes from two parts: (1) kinetic (related to temperature) and potential (related to the forces between particles).

• If everything else is equal, then the bigger the object, the more internal energy it has.

Internal Energy

• The internal energy of an object can increase by increasing the electrical potential energy between particles, by bending molecules, compressing or stretching molecules.

• In the main, if you heat up an object, its internal energy will increase due to an increase in its temperature. The particles will be moving faster.

Thermal Energy

Sadly, this phrase is used in two ways:– it can mean “internal energy”– It can mean “heat”

Heat Capacity (thermal capacity)

• If you add 12 Joules to a bowling ball, it’s temperature will go up 6 ˚C.

• If you add 6 J to the same ball, it will go up by ___ ˚C.

• The Heat Capacity of that ball is 2 J ˚C-1.• Heat Capacity tells you how much energy you

need to add or subtract to change the temperature of that object by 1 degree.

Heat Capacity (thermal capacity)

• If you add 12 Joules to a bowling ball, it’s temperature will go up 6 ˚C.

• If you add 6 J to the same ball, it will go up by 3 ˚C.

• The Heat Capacity of that ball is _ J ˚C-1.• Heat Capacity tells you how much energy you

need to add or subtract to change the temperature of that object by 1 degree.

Heat Capacity (thermal capacity)

• If you add 12 Joules to a bowling ball, it’s temperature will go up 6 ˚C.

• If you add 6 J to the same ball, it will go up by 3 ˚C.

• The Heat Capacity of that ball is 2 J ˚C-1.• Heat Capacity tells you how much energy you

need to add or subtract to change the temperature of that object by 1 degree.

Heat Capacity (thermal capacity)

• C = Q / DT• In general, the bigger the object, the greater

its Heat Capacity.

Specific Heat Capacity

• The Specific Heat Capacity does not depend on the size of the object.

• All iron takes the same amount of heat to raise 1 gram by 1 ˚C. So this is almost the same as Heat Capacity, but it’s not for one object, it’s for one material.

• It takes 4200 Joules to raise 1 kg of water by one degree.

• c = Q / ( mDT )

Name that state

• The particles move around nicely. They flow.• The particles are close to each other.• The particles take the shape of their container.

LIQUID

• The particles move around nicely. They flow.• The particles are close to each other.• The particles take the shape of their container.

Name that state

• The particles move around nicely. They flow.• The particles are far from each other.• The particles take the shape of their container.

GAS

• The particles move around nicely. They flow.• The particles are far from each other.• The particles take the shape of their container.

Name that state

• The particles wiggle in their places.• The particles are close to each other.• The particles form their own shape.

SOLID

• The particles wiggle in their places.• The particles are close to each other.• The particles form their own shape.

Name that phase change:

• From Solid to Liquid:

Name that phase change:

• From Solid to Liquid:• Melting

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas• Boiling (evaporation is OK)

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:• Condensation

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:• Condensation• From Solid to Gas:

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:• Condensation• From Solid to Gas:• Sublimation

Name that phase change:

• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:• Condensation• From Solid to Gas:• Sublimation• From Gas to Solid:

Name that phase change:• From Solid to Liquid:• Melting• From Liquid to Solid:• Freezing• From Liquid to Gas:• Boiling (evaporation is OK)• From Gas to Liquid:• Condensation• From Solid to Gas:• Sublimation• From Gas to Solid:• Deposition

Specific Latent Heat of Fusion (LF)

• It takes energy to turn a solid into a liquid, and the more material you have, the more energy it takes.

• This energy is called the latent heat of fusion, and since it depends on mass, it is the “Specific Latent Heat of Fusion.”

• L = Q / mass• It is measured in Joules per kg, (or J kg-1).

Specific Latent Heat of Vaporization (LF)

• It takes energy to turn a liquid into a gas, and the more material you have, the more energy it takes.

• This energy is called the latent heat of vaporization, and since it depends on mass, it is the “Specific Latent Heat of Vaporization.”

• L = Q / m

Evaporation vs. Boiling (slide 1 of 3)

• Evaporation happens only at the surface of a liquid. Fast molecules escape the attractive forces of the other molecules.

• Since only the fastest particles leave, the remaining liquid is cooler than the original.

Number of Particles vs. Speed

NumberOf

Particles

Speed

Kinetic Model of an Ideal Gas

• Overheads about Boyle’s law• Overheads about Charles’s law• Overheads about Gay-Lussac’s law

Piston

Why does a balloon get bigger as you blow it up?

Why does a balloon get bigger as you blow it up?

• One answer is that, from PV = NRT, the greater the number of particles, the greater the volume.

• Another answer is that with more particles in the balloon, there is an increase in how often (how frequently) the inside of the balloon is hit by an air molecule. This is the very essence of pressure. The increased pressure forces the balloon outwards.

Evaporation vs. Boiling

• This is how perspiration works.• Boil water and the bubbles start at the bottom

of the pot. What is in the bubbles?