Unit 3- Energy Notes

Model so far… Unit 1

Model so far… Unit 2• Over the next week copy Model 2 onto your

Model So Far… handout.

Add to our model• Key Concept 1: When matter- In any of its

three states– gets hot, Its particles go faster and take up more space, and the solid, liquid or gas expands.

• Key Concept 2: When matter- In any of its three states– gets cold, Its particles go slower and take up less space, and the solid, liquid or gas contracts.

How a thermometer works.

• A thermometer works because of the expansion and contraction of alcohol. The substance found in classroom thermometer.

• Key Concept 3: The expansion of a substance can therefore be used to measure temperature itself. A device which does this is called a “hotness-meter” or thermometer.

• Key Concept 4: On the Celsius scale thermometer, the level to which the alcohol (or mercury) contracts at the freezing point of water is labeled 0 C, and the level to which alcohol expands at boiling point of water is labeled 100 C.

• Heat Transfer by Conduction

Hotness….

Hotness….

Hotness….• Key Concept 5:

Post it Challenge

• Write one sentence that shows how energy, temperature and heat are related.

• Put your name on the back and come stick it to the board.

Closure• The system with the most heat will burn you

the worst (200mL boiling water). Write the question below and think!

Why can dry ice, solid CO2 burn you, but CO2 in the gas phase cannot? Gases have more kinetic energy then liquids or solids.

Energy

• Key Concept 6 :Energy is the stuff that make particle do stuff.

Problem with Energy in Education

• Treatment of energy is inconsistent from discipline to discipline.

• Students cannot use energy to adequately describe or explain everyday phenomena.

• Students are taught that energy comes in different forms or types.

Energy• When “changing one form of energy into

another”1 implies that there are different “kinds” of energy

• “Forms of energy” - implies that somehow energy is changing

• This makes it difficult for students to describe the changes in matter.

• Remember: HOMEWORK- DUE FRIDAY1- American Association for the Advancement of Science, Project 2061 Benchmarks Online,

1,2, 3’s of eNeRGy• Key Concept 7:

Why does a solid have a definite shape?

Icy Hot Lab• Will not be done in your Lab Notebook.

• Key Concept 8: Goal of Icy Hot Lab: How does the temperature of water change when energy is added?

• Key Concept 9: Your Prediction

My Notes

Temp and time when all ice was melted:

Temp and time when the water started to boil:

Any other important notes/observation

Icy Hot Board Meeting

• Working with your desk pods

1. Divide your heating curve into three regions (A,B, and C); label each region:

• (A) a low temperature plateau• (B) a region of temperature change• (C) a high temperature plateau

2. State what phases were present at A, B, and C

3. Draw a model at the particle level that shows how the water particles were behaving.

4. How does your groups final white board compare to your prediction (Key Concept 9).

Icy Hot Board Meeting

Icy Hot DiscussionWhy does a solid have a definite shape?

Intermolecular Forces• There are forces of attraction and repulsion that

exist between particles (molecular) of all substances.

• These intermolecular forces allow molecules to pack together in the solid and liquid states.

• Key Concept 10: All phase changes involve either an increase or decrease of intermolecular forces. In your Icy Hot Lab the energy added during the temperature plateaus went to break up these intermolecular forces.

Intermolecular Forces

Icy Hot Conclusion Questions

Room Number is: 169429

For each of the phase changes below, choose whether intermolecular forces increase or decrease.

Phase Change Name Intermolecular Forces Increase or Decrease

1) Solid to Liquid Melting or Fusion (T) Increase(F) Decrease

2) Liquid to Gas Evaporation or Vaporization

(T) Increase(F) Decrease

3) Gas to Solid Deposition (T) Increase(F) Decrease

4) Liquid to Solid Freezing or crystallization

(T) Increase(F) Decrease

Intermolecular Forces

In a phase change, does the distance between molecules increase or decrease?

When considering phase changes, the closer molecules are to one another, the stronger the intermolecular forces.

Key Concept 11: Heating Curve

Key Concept 12: Cooling Curve

Room Number is: 169429

1. In what part of the curve would substance X be a liquid?

2. In what part of the curve would substance X be a solid?

3. What part of the curve represents a mixed liquid/gas phase of substance X?

4. What is the melting temperature of substance X?

5. What is the boiling temperature of substance X?

Room Number is: 169429

What is the boiling point of the substance?

(a) 0°C (c) 12°C

(b) −50°C (d) 75°C

What state of matter is the substance at 50°C?

(a) gas (c) solid

(b) liquid (d) not enough information

Energy Bar Charts• Better know as:

• Key concept 13: Energy bar charts are how we can represent the role of energy when a system is changed.

Constructing an Energy Bar Chart

Consider this example

A cup of hot coffee cools as it sits on the table.

• 1. Determine what is in the system

• Everything else makes up the surroundings

cup coffee

Decide whether Ech is involved

• In this case, you start with coffee and end with coffee; particles are not rearranged to form new substances

• So, ignore Ech for now.

Assign values to Eph

• Key Concept 14: Due to interactions between particles, the energy stored due to the arrangement of particles is ranked:solids < liquids < gases

• We choose to represent these phases by using:

Solids = 1 bar

Liquids = 2 bars

Gases = 4 bars

Assign values to Eph

• Use two Eph bars before and after

Choose bars for Eth depending on temperature

• Use 4 bars for hot coffee and 2 bars for room temp coffee

• Other values might also work; try to be consistent in your representations

Now show energy transfer

• Final situation has 2 less bars of E than initial; 2 bars had to leave the system

Now, consider phase change

• A tray of ice cubes (-8 ˚C) is placed on the counter and becomes water at room temperature

• What do we know about the situation?

• The system is the tray of ice cubes.

• The solid water turns to liquid water - no change in Ech

• The Eph increases (solidliquid)

• The Eth increases (temp rises)

• Now represent these changes in bar graph.

Initial & Final States

• Choice of bars for Eth arbitrary, but consistent.

• I generally use 2 bars for room temp and one bar for cold liquid, -8˚C should be < 1 bar.

Account for Energy• Energy must flow into system via heating

Add to Key Concept:11

Q= En-ergy

Add to Key Concept: 12

Q= En-ergy

Bellringer

How much Q?• We are now interested in learning just how

much energy transferred during these changes.

• Update our initial thought trifold again.

White Board Questions

With your desk partner pick one of the three demos and answer the following questions on your white board. (Demo1: Red, Demo 2: Blue, Demo 3: Green)

1) What demo are you going to describe?

2) During your demo did your objects (balloons, ice or cubes) gain or lose heat?

3) Did the objects gain or lose heat at the same rate?

White Board Questions

4) What do you think accounts for the different rates of energy transfer (or heating)?

5) Imagine you are given 1g of copper and 1g of wood at room temperature. If you wanted to raise that 1g sample 1C° which substance would require more energy?

Quick review

Units of Energy

Measuring Energy

• Key Concept 15:A calorie is defined as the amount of energy required to raise the temperature of one gram of water one degree Celsius.

• Food is measured in Calories, or 1000 calories (kilocalorie).

• Key Concept 16 :A joule is the SI unit of heat and energy, equivalent to 0.2390 calories.

Specific Heat

• Key Concept 17:The specific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius.

• Some objects require more heat than others to raise their temperature.

Key Concept 18: Specific Heat is an intrinsic property, it is independent of how much of the material is present.

Specific Heat

Specific Heat

Demo1- Water: 4.184 J/gC

Air: 1.02 J/gC

Demo 2- Plastic- 2.3 J/gC

Steel: 0.46 J/gC

Demo 3- Copper: 0.386 J/gC

Wood: 0.6 J/gC

White Board Questions

Move your desk into desk pods. Let the duel begin.

5) What the specific heat for wood and copper in a complete sentence.

Copper: 0.386 J/gC

Wood: 0.6 J/gC

White Board Questions

6) If you had 10 grams of copper and wanted to raise it 10 degree C, how much energy would that take? The specific heat of copper is 0.386 J/gC.

White Board Questions

6) If you had 10 grams of copper and wanted to raise it 10 degree C, how much energy would that take? The specific heat of copper is 0.386 J/gC.

7) What is I wanted to decrease the temperature of 10 gram sample of copper 10 degree C? How much energy would need to be removed?

Desk Pod Challenge As a desk pod combine your thoughts and solve this problem. Show all your work on one of the white board. Please, draw a picture to help illustrate how you came to any answer.

8) What if you had 3 grams sample of water and wanted to raise it 2 degrees C, how much energy would it take?

4.18 J/gC

1g 1g1g

Desk Pod Challenge

9) What if you had 30 grams of water and wanted to decrease the temperature 25 degrees?

4.18 J/gC