Share Your Answers with Your Lab Group. Come to Consensus with Your Answers and Share Them

/ Lesson 8 Energy Transformations
California Standard Addressed
3. Energy cannot be created or destroyed, although in many processes energy is transferred to the environment as heat. As a basis for understanding this concept:
3.a. Students know heat flow and work are two forms of energy transfer between systems.
3. b. Students know that the work done by a heat engine that is working in a cycle is the difference between the heat flow into the engine at high temperature and the heat flow out at a lower temperature (first law of thermodynamics) and that this is an example of the law of conservation of energy.
3. c. Students know the internal energy of an object includes the energy of random motion of the object’s atoms and molecules, often referred to as thermal energy. The greater the temperature of the object, the greater the energy of motion of the atoms and molecules that make up the object.
3. d. Students know that most processes tend to decrease the order of a system over time and that energy levels are eventually distributed uniformly.
3. e. Students know that entropy is a quantity that measures the order or disorder of a system and that this quantity is larger for a more disordered system. / DO NOT WRITE ON THIS HANDOUT

Engage

/ Record your responses to these questions in your lab journal.
1. What do you think this picture is about?
2. Can a small object deliver energy in a collision?
3. What delivers more energy, a slow pitch or a fast pitch?
4. What about tiny particles – atoms and molecules? Can they deliver energy in a collision?
5. Examine the diagram below the batter. Predict which thermometer will record a higher temperature. Support your answer.
/ 6. Imagine that you measure the temperature of the bb’s before you drop them, and after you drop them. How would the temperatures compare? Why would there be a difference?

Share your answers with your lab group. Come to consensus with your answers and share them with the class.

Explore

You will now make some predictions about temperature and the speeds of the particles in a system.

The teacher will either demonstrate or allow the students to go to the following web page:

The kinetic energy of the particles in the system may be increased by moving the heater temperature slider.

Predictions

7. What do you predict will happen to the speed of the gas particles in the container as the temperature is increased or decreased?

8. What do you predict will happen to the pressure in the container as the temperature is increased or decreased?

Evidence

9. What happened to the speed of the gas particles in the container as the temperature was increased or decreased?

10. What happened to the pressure in the container as the temperature was increased and decreased?

11. Compare your predictions to the evidence. Were your ideas supported or has your thinking changed?

The kinetic energy of a particle is determined using the following equation:

KE= Kinetic Energym=massv=velocity

12. Describe the average kinetic energy of the particles in a material that has a high temperature (high or low).

13. Describe the average kinetic energy of the particles in a material that has a low temperature (high or low).

13b. How can you explain that the pressure in the container increased when the temperature and therefore the kinetic energy of the gas particles increased?

You will now make some predictions about temperature and energy transferred to a system.

Imagine that you have a jar filled with bb’s.

You wrap paper towels or some other insulating material around the jar.

You shake the jar vigorously.

Predictions

14. What do you predict would happen to the temperature of the bb’s as the jar is shaken?

15. Why do you think this will happen?

16. What is the purpose of the paper towels?

Set Up / Evidence
bb temperature
(°C) / 17. Compare your predictions to the evidence. Were your ideas supported or has your thinking changed?
18. As the time the bb’s were shaken increased, what happened to the final temperature?
19. If the temperature of the bb’s increased, what can we say about the average kinetic energy of the particles in the bb’s?
Use the temperature probe to determine the temperature of the jar before being shaken.
Use the temperature probe to determine the temperature of the jar after being shaken for 1 minute.
Use the temperature probe to determine the temperature of the jar after being shaken for 2 minutes.
Use the temperature probe to determine the temperature of the jar after being shaken for 3 minutes.

20. If the average kinetic energy of the particles in the bb’s has increased, has energy been added to the bb’s or removed from the bb’s during the shaking?

21. Complete the following energy transfer diagram.

Person BB’s

When the temperature of a material increases, we understand that the average kinetic energy of the particles in that material has increased.

We use the terms internal energy or thermal energy to describe the energy in an object resulting from the motion of the particles in the object.

James Prescott Joule first discovered that the energy used to stir up water was found to increase the temperature of the water.

Through careful experiments he also noticed that there was NO DIFFERENCE in the amount of energy used in the stirring, and the energy gained by the water.

We refer to this relationship as the LAW OF CONSERVATION OF ENERGY today. (∆Usystem =0)

Explain

/ 22. This device was invented by James Joule. Predict how the change in GPE of the falling mass compares to the gain in molecular kinetic energy experienced by the water.

23. What is temperature a measurement of?

24. What happens to the gravitational potential energy stored in a book that falls off of a table onto the floor?

25. Complete the following diagrams for the event shown in the illustration.

A bag of bb’s are dropped. / Before the drop Right before Landing At Landing

TOTAL ENERGY

Elaborate

Consider this set up.

/ A peanut is placed below a sealed test tube half-filled with water.
A syringe is connected to the sealed test tube.
A mass is placed on the top of the syringe.
The peanut is lit on fire.
It burns for a short time and the water boils.

Predictions

26. What do you predict would happen to the temperature of the water in the test tube?

27. Why do you think this will happen?

28. What do you think the expanding gas above the water will do to the piston in the syringe?

29. What do you think will happen to the mass resting on the syringe?

30. What affect will this have on the Gravitational Potential Energy of the mass resting on the syringe?

Evidence

31. The teacher will light the peanut on fire. Record your observations in detail about the event. Include information about the way the peanut burns, what happens to the outside of the test tube, what happens inside of the test tube, what happens to the syringe, and what happens to the mass.

31. Compare your predictions to the evidence. Were your ideas supported or has your thinking changed?

32. Prepare an energy transfer diagram for this event.

33. Prepare pair of energy bar graphs for this event.

34. Assuming no losses to the external environment, how does the starting peanut chemical potential energy compare to the final gain in gravitational potential energy by the mass?

A device that converts internal energy into mechanical energy (GPE or KE) is defined to be a HEAT ENGINE. The syringe and the contained liquid water, steam and air serve as an example of a simple heat engine. The chemical potential energy of the peanut is converted to internal energy of the material contained in the heat engine, and then into mechanical energy.
The basic operation of a heat engine can be defined by the diagram shown on the right. /
/ 35. Select the answer that best represents the work done by the heat engine described by the diagram .
The work done by the heat engine is...
(a) 700. joules
(b) 500. joules
(c) 200. joules
(d) 300. joules / 36. A heat engine has 700. joules energy added to it from a high temperature reservoir. The heat engine does 200. joules of work.
Select the answer that best represents the amount of energy exhausted to the low temperature reservoir.
The amount of energy exhausted is...
(a) 700. joules.
(b) 200. joules.
(c) 900. joules.
(d) 500. joules.
37. A heated gas expands, raising a piston. Which of the following describes the energy exchanges of this process?
(a) Energy is transferred to the gas by the piston, and to the piston from the heat source.
(b) Energy is transferred to the gas from the heat source, and to the raised piston from the gas
(c) Energy is transferred to the gas in the form of heat and work done by the piston.
(d) Energy is transferred directly to the piston from the heat source.
38. The pressure of a gas inside a closed, rigid container will increase when the gas temperature increases. The pressure of the gas increases because the
(a) density of the gas decreases.
(b) rate of collisions of gas molecules with the surface increases.
(c) container expands in size when heated.
(d) gas molecules bond together to form more massive molecules.
/ 40. If you drop a ball, the height of the bounce decreases with each successive bounce. Why?
A.B. / 41. A cup of hot coffee sits on a table. Which of these two pictures best describes the direction that energy moves?

42. Prepare the table below in your lab notebook. Record your predictions.

Set Up / Predictions / Data
/ What will happen to the temperature of the water in the flask when it is placed in the beaker? / What happened to the temperature of the water in the flask when it is placed in the beaker?
What will happen to the temperature of the water in the beaker when the flask is placed in the beaker? / What happened to the temperature of the water in the beaker when the flask is placed in the beaker?
Draw lines on this graph to describe the change in temperature that you will observe for the flask and the beaker. / Draw lines on this graph to describe the change in temperature that you observed for the flask and the beaker.

43. Prepare the table below in your lab notebook. Record your predictions.

The teacher will check your table and predictions before you can use the equipment.

44. Prepare the table below in your lab notebook. Record your predictions.

Set Up / Predictions / Data
An insulating wrap is placed around a beaker containing warm water. Another beaker containing warm water is left on the counter.
/ What will happen to the temperature of the water in the beaker if the wrap is placed around it? / What happened to the temperature of the water in the beaker with the wrap?
What will happen to the temperature of the water in the beaker if no wrap is placed around it? / What happened to the temperature of the water in the beaker with no wrap?
Draw lines on this graph to describe the change in temperature that you will observe for the wrapped and unwrapped beaker. / Draw lines on this graph to describe the change in temperature that you observed for the wrapped and unwrapped beaker.

Explain II

45. Compare your predictions to the evidence. Does the evidence support your predictions?

46. Describe the trend in temperature change when warm objects are placed in a cooler environment.

47. Does an insulating blanket increase the temperature of an object? What is the affect of an insulating blanket?

48. Based on the data, explain whether internal energy moves from high temperature reservoirs to low temperatures or in the opposite direction.

49. Movement of energy from concentrated states to less concentrated states results in an increase in the disorder of the system. This randomness is defined as ENTROPY. Describe whether the entropy increased or decreased in the last two set ups.

Evaluate

50. An engine has an input of heat energy of 10,750 J and does 2420 J of work. Which of the following is the heat loss?

(a) 0.225 J

(b) 4.44 J

(d) 13,170 J

51. A proposed ideal heat engine would run with a high temperature reservoir at 800 kelvin and a low temperature reservoir at 300 kelvin. When the engine is running, it extracts 400 joules of energy from the hot reservoir and does 250 joules of work each minute. How much energy is expelled to the low temperature reservoir each minute?

(a) 150 J (b) 250 J (c) 300 J (d) 400 J

52. When a gas is heated in a closed container, the internal pressure increases. Which best describes the reason for the increase in pressure?

(a) The average kinetic energy of the gas molecules decreases.

(b) The potential energy of the gas increases.

(d) The potential energy of the gas decreases.

53. A gas in a sealed cylinder is heated. What can be noticed about the gas molecules?

(a) the gas molecules move faster

(b) the gas molecules have greater kinetic energy

(d) the answers above are all correct

54. Which of the following does not increase as the gas is heated?

(a) the average number of gas molecules hitting the cylinder walls per second

(b) the average kinetic energy of the gas molecules

(d) the average distance between the gas molecules.