Heat

1. To change a substance from solid to liquid, is heat ADDED or REMOVED?

Added

What causes phase changes?

Addition/removal of heat (add more KE, from solid --> gas, remove KE, from gas --> solid

Which method of heat transfer takes place in heat from a campfire?

Radiation

Which method of heat transfer takes place in microwaves?

Radiation

2. To change a substance from liquid to solid, is heat ADDED or REMOVED?

Removed

3. To change a substance from gas to liquid, is heat ADDED or REMOVED?

Removed

What does the amount of heat something has depend on?

Two factors: - The temperature of a substance (how fast the particles are moving) - The mass (how many molecules there are in the substance)

When a gas reaches its condensation point, it phase changes to a

liquid

When a solid reaches its melting point, it phase changes to a

liquid

Thermometers

measure temperature

When a liquid reaches its freezing point it phase changes to a

solid

Convection current

the movement of a fluid caused by density differences

Conductor

- A material that conducts heat well - Include metals and silver (why you may use a metal bowl to heat up something) - Why a metal bench is really hot in the summer, traps in all of the heat

Temperature

- A measurement of thermal energy/how much kinetic energy is in an object - A measure of how hot (or cold) something is compared to a reference point (a set temperature you can refer to, like freezing/boiling points); specifically, a measure of the average kinetic energy of the particles in an object. - The speed that particles move, determined by how much KE they have

Solids

- Definite shape and volume - low KE, particles packed tightly together

Temperature is measured in...

- Fahrenheit scale (U.S.) - Celsius scale (rest of the world) - Kelvin (scientists) --> 0 K = absolute zero

Liquids

- Indefinite shape and definite volume - More KE than solids, particles still close together - Keeps the shape of its container

Insulators

- Materials that do not conduct heat well, opposite of conductors - Include wool, plastic, and glass (transfers heat easily - If a soup is really hot, then take a plastic spoon instead of a metal one so that you don't burn yourself

Gases

- No definite shape or volume - High KE, particles are spread out and have a lot of space between them - Expand to fill their container

Earth's energy sources

- Solar radiation: visible light, infrared radiation, and other types of radiation - Residual thermal energy from when the Earth was formed is slowly released - Decay of underground radioactive elements --> produces energy

Kinetic Theory of Matter

- The idea that the atoms and molecules that make up all matter are moving constantly and in every direction randomly. - All matter is made of small particles that are in random motion and that have space between them

Absolute zero

- The lowest temperature possible when particles have no kinetic energy - 0 K - -273 C - -459 F

Thermal energy

- The total energy of ALL the particles in an object - Depends on the temperature of the object and the number of particles in that object - the more particles = more thermal energy

Radiation

- The transfer of energy by electromagnetic waves that carry radiant energy - Doesn't require any matter, can occur in a vacuum - You can feel radiation from an object without touching it, like the sun - Heat radiation = infrared radiation - E.g: feeling warm when standing next to a campfire - Solar radiation: the transfer of radiant energy from the sun

Heat

- The transfer of thermal energy between objects - Objects must have a difference in temp - Flows from hot to cold - Warmer object will cool down while cooler object warms up until both are the same temperature (equilibrium is when heat stops transferring) - Measured in Joules

What happens to atoms the more they move?

- They become hotter because of microscopic friction.

Conduction

- Transfers heat between 2 objects (one particle of matter to another) - The transfer of heat energy by direct contact between particles - Heat is transferred from matter with a higher temperature and greater kinetic energy to matter with a lower temperature and less kinetic energy. - Thermal conductors, such as metals, transfer heat easily - Insulators (such as wood and air) E.g: - When heating up soup, the particles from the pot touch the particles of the soup. Since the particles of the pot are hot, the particles move faster. When they touch the soup, the soup's particles start to move faster, and the soup becomes hot.

Convection

- Transfers heat through FLUIDS (liquids + gases), like water or air - Transfer of heat energy by hot matter rising and cool mater sinking due to density - The movement of heat from hot to cold within a lava lamp - Due to a difference in density, hot fluid (low density) moves to cold fluid (high density) E.g: - When air is heated, it becomes less dense, so it floats to the top - Cool air becomes more dense, so it sinks to the bottom - This repeats over and over again, causing a convection current, causing wind and different weather patterns - E.g: lava lamp

Phone heat analogy

- When it is cooling down, particles move slower, so there is less KE - When it is hot, particles move faster, so there is more KE

Heat transfer

- When thermal energy is transferred from a hot substance to a cold substance, a change in temperature occurs. The more thermal energy transferred from one substance to another, the greater the temperature change. Therefore, heat is measured by how much of a temperature change it produces when it is transferred from one substance to another.

Which has more thermal energy: A 2 L cup of milk at 70 F or a 1 L cup at 70 F?

2 L cup because it has more mass = more milk/particles = more thermal energy

How can you measure how much thermal energy (heat) a substance absorbs or releases?

By measuring the substance's temperature

List these from least thermal energy to most thermal/heat energy: A, 300 mL of water at 50 C, B, 500 mL at 70 C, C, 300 mL at 25 C, or D, 500 mL at 50 C

C, A, D, B

Touching a hot coffee mug

Conduction

Which method of heat transfer takes place when frying an egg?

Conduction

Which method of heat transfer takes place when blowing hot air from a hair dryer?

Convection

Which method of heat transfer takes place when warm air rises and cool air sinks in a refrigerator?

Convection

If the molecules in a substance move slower, then the temperature will...

Decrease

Which state of matter have the highest temperature? The most absorbed thermal KE? The most KE?

Gases

Why does a substance's temperature increase with heat/thermal KE?

Heat/thermal KE is added, increasing the KE of the atoms, and thus increasing the temperature

Why is "close the door, you're letting the cold air in" inaccurate?

It should be, "you're letting the hot air out and lowering the average KE (temperature)

Can objects contain heat?

No, but they do have thermal energy

Are heat and temperature the same?

No, temperature measures heat

Why do molecules and atoms eventually slow down?

They cool down because friction converts mechanical energy into thermal energy, forcing molecules and atoms to release some of their energy to their surroundings.

Methods of heat transfer

conduction, convection, radiation

Heat stops flowing when...

equilibrium is reached, or when both objects reach the same temperature

When a liquid reaches its boiling point, it phase changes into a

gas

As the mass of the substance increases (there are more atoms or molecules in the substance), the amount of heat energy in that substance will...

increase

As the temperature increases (because the atoms or molecules in the substance are moving faster), the amount of heat energy in that substance will...

increase

If the molecules in a substance move faster, then the temperature will...

increase