Thermal Energy Test

Which direction does heat flow? Give an example.

"Heat flows from a high to a low." A spoon left in a pot of boiling water will absorb the heat which will transfer to your hand if you touch it.

Potential Energy

(Between molecules) the measure of the attraction between molecules.

Describe what happens to motion and spacing of molecules when heated or cooled for a liquid, solid, and gas.

*liquid : as the temperature increases, molecules increase speed, and use more space *solid : as the temperature increases, molecules increase in speed and use more space *gas : as the temperature increases, molecules increase speed and use more space

Calculate the heat input (or output) required to change the temp rapture of 3kg of iron by 3 degrees Celsius.

3kg x 3*C x 452c =4068J

The following objects are all heated from 10*C to 30*C. Which object will transfer the most energy to your hand?

5kg apples (largest).

Using thermal expansion and contraction, describe how a liquid thermometer works.

As the temperature increases, the volume of the liquid increases, causing the liquid in the thin tube to rise (thermal expansion). As the temperature decreases, the volume decreases and the level in the tube goes down (thermal contraction).

All of the following are examples of conductors except _______

Air. (choices: silver, water, air, aluminum)

1st Law of Thermodynamics

All energy is conserved.

2nd Law of Thermodynamics

Heat (energy) flows from a high temperature to a low temperature.

Do all objects emit the same amount of radiation? Why or why not?

Hotter objects transfer more heat through radiation. They have more heat to release.

What two types of energy do molecules possess?

Potential & kinetic.

Two objects it the same material but different masses are subjected to the same thermal energy input.

The object with the less mass will experience a greater change in temperature.

Thermodynamics

The study of heat and work.

Thermal Energy

The sum of potential energy and kinetic energy.

Conduction

The transfer of heat between adjacent objects.

Convection

The transfer of heat between locations, liquid and gas.

Radiation

The transfer of heat using electromagnetic waves.

Heat

The transfer of thermal energy from high to low.

Thermal Equilibrium

There is no exact change of energy, objects are the same temperature. There is no heat.

Provide an example of when two substances might have the same temperature but different thermal energy.

Two substances may have the same temperature, but different thermal energy when there is not the same amount of each substance.

Which is an expanse of heat transfer by convection?

Water boiling in a pot on the stove.

Thermal Contraction

When temperature decreases, molecules move more slowly and come together.

Thermal Expansion

When temperature increases, molecules move faster and spread apart.

Work

A force applied to an object that moves in response.

Which of the following is an example of energy conservation?

A hockey puck slides to a stop due to friction.

If you wanted to boil water quickly in a tea kettle, what kind of material would you use for the tea kettle?

A metal such as aluminum or copper.

Conduction occurs primarily in solids. Why?

Because the molecules are closer together.

Which will cool fastest initially in a room temperature room? Boiling water or lukewarm water?

Boiling water will lose heat (cool) faster.

Describe characteristics of three temperature scaled including freezing and boiling point of water for each.

Celsius: boiling-100 freezing-0 & 1degree c =1K Kelvin: boiling-373K freezing-273K Fahrenheit: boiling-212 freezing-32 & I degree f< 1 degree c

What energy conversions are involved in a heat engine?

Chemical to thermal to mechanical

What are the three methods of thermal energy transfer? Give two examples of each.

Conduction, convection, radiation.

What is the primary difference between conductors and insulators?

Conductors have "loose" electrons, they transfer energy easily. Insulators do not transfer as easily.

Give several examples of conductors and insulators.

Conductors: silver, copper, gold and aluminum Insulators: rubber, dry wood and dry paper, many plastics, glass, ceramics

State wether the variable is "inversely" or "directly" proportional to the temperature change. (Mass, specific heat, and thermal energy transferred.

Consider specific heat. a. Mass- an increase in mass will slow the temperature change (inversely). b. Specific heat capacity- an increase in the specific heat capacity will slow the temperature change (inversely). c. Thermal energy transferred- directly, more transfer = more temperature change.

Heat Engine

Converts heat energy into mechanical energy.

Specific Heat

Describes the energy needed in Joules to raise of 1kg of a substance by 1*C.

Calculate the final temperature of 0.020 kg of mercury that loses 500J of thermal energy and started with a temperature of 400 Kelvin.

J=mass x specific heat x temperature change

If you wanted to maximize heat transfer, what kind of material would you use? How about if you wanted to minimize heat transfer?

Metal. Something porous (having holes).

Will heat flow between two objects touching that have the same temperature? Why or why not?

No, there is a gradient (difference) of temperatures,!/9 no heat will be exchanged.

Insulators

Objects that transfer hear poorly.

Conductors

Objects that transfer heat easily.

What state of matter has the most potential energy? The least?

Solid. Gas.

Explain why thermal energy and temperature, though related, are different.

Temperature is the measure of the average kinetic energy (motion). Thermal energy included temperature and potential energy.

How are temperature and kinetic energy related?

Temperature is the measure of the average kinetic energy.

What does a thermometer measure?

Temperature, which is the average kinetic energy of the molecules.

If you have several spoons made of conducting materials and insulating materials, which would feel cooler to the touch and why?

The conducting, because it will transfer the heat to my hand.

Suppose you took a bite of pie that was at a certain temperature. The crust doesn't burn you but the filling does. Using the idea of specific hear, explain why the filling burned you but the crust didn't even though they had the same temperature.

The crust is an insulator, and the filling acts as a conductor.

Kinetic Energy

The energy of motion.

A 80*C object and a 60*C object sit (not touching) in a 21*C environment. Which best explains what will happen?

The environment will get warmer.

How are heat flow and temperature differences related?

The greater the difference between temperatures, the more heat will flow.

Temperature

The measure of the average movement of molecules.

Entropy

The measure of the disorder of a system.

Recall the video shown in class of the bimetallic strip that was bent when it was heated. Explain why it bent. (HINT: Remember that the strip was made of two different metals)

The metals have different specific heats, and different expansion rates. One metal stretches more, and causes the bending.

Complete the following conversions; a. 37*C to Fahrenheit b. 384 Kelvin to Celsius c. -45*C to Kelvin d. 45*F to Celsius

a. 98.6 b. 111 c. 228 d. 7.2

When energy is transferred as heat, the amount of useable energy _____.

decreases.

An insulator is a material that has molecules that _______

do not transfer heat easily.

When a liquid is cooled, the liquid molecules _______

move slower than before.

This type of heat transfer can occur in outer space.

radiation!