ENERGY

IRP Binders & Log Books

Name on log bookName(s) on binderRubric clipped to contents pageLog book(s) placed into binderStack binders NEATLY (turn opposite

directions) at designated location for your class.

Whiteboard Icy Hot Lab Conclusion Questions

Group F #1Group E #2Group D 3 iGroups C & G #4 – Region AGroup B #4 – Region BGroups A & H #4 – Region C

Changes to Calendar!

ALL ISEF Forms (if they are not in your binder) – due 9/23

Unit 3 WS1 is not due MondayWe will discuss Energy Bar Charts on

MondayIcy Hot Lab (due 9/24)

ENERGY

substance-like quantity present in every system of particles

always involved when a system undergoes change

ENERGY in a system:

Thermal -- energy of motion (“Eth account”) depends on mass and velocity of particles temperature of a system is a measure of how fast

particles are moving

Phase -- energy due to arrangement/orientation of particles which have an attractive force between them (“Eph account”) attractions lower energy of a system solids have lowest Eph, liquids have greater Eph, and gases have the greatest Eph

ENERGY in a system:

Energy can be transferred between “accounts” within the system of particles

OR Energy can be transferred into or out of a

system of particles

A change in temperature or phase is observable evidence of transfer of energy

TRANSFER OF ENERGY between the system and the surroundings

Heating – transfer of energy through collisions of particles

Working – transfer of energy when macroscopic objects exert forces on each other

Radiating – transfer of energy by the emission or absorption of light

LAW OF CONSERVATION OF ENERGY

Energy can not be created or destroyed

Total amount of energy remains the same during all energy transfers

HEAT AND TEMPERATURE

Heat is a measure of energy transferred into or out of a system through collisions of particles

Temperature is a measure of how fast the particles are moving

MEASURE OF TEMPERATURE

Celsius Scalefreezing point of water is set at 0oCboiling point of water is set at 100oCinterval between them is divided into 100 parts

Kelvin Scaleabsolute zero – theoretically the lowest possible temperature

particles stop movingabsolute zero = 0 K = - 273oCthe size of each degree (interval) is the same as Celsius

Icy Hot Lab –copy notes into lab notebook

Changes in physical arrangement of particles

Energy used to break attractions between particles of solid

Both solid & liquid present

Tem

pera

ture

Time (Energy)

A

Icy Hot Lab Changes in speed (motion) of

particles Energy used to speed up

particles of liquid Liquid only present

Tem

pera

ture

Time (Energy)

B

Icy Hot Lab Changes in physical

arrangement of particles Energy used to break

attractions between particles of liquid

Both Liquid & gas present

Tem

pera

ture

Time (Energy)

C

Problem QuestionPrediction graph (Title, axes labeled)Copy of your actual graph, labeled

according to data processing instructions

Answers to conclusion questions in complete sentences that stand alone.

Icy Hot Lab “Report”

Review of types of change – help for lab conclusions

Chemical change – a new substance is made

Physical change – no new substance made (phase change)

Energy Bar Charts – refer to Energy Bar Charts notes

How to represent the role of energy in physical change

© Modeling Chemistry 2007

Tracking Energy…

We were able to discuss how energy was transferred to the system (heating) and how the system responded (changes in particle motion or arrangement.

It would be helpful if we could keep track of how energy is transferred and stored. Representation Tool = Energy Bar Charts.

Constructing an Energy Bar Chart

Consider the Lab

A beaker of liquid water is heated over a Bunsen burner.

1. Represent the process with a temperature – time graph. Then make an empty Energy

Bar Chart

Constructing an Energy Bar Chart

2. Determine what is in the system Write it in the center circle, which represents

the system.

Everything else makes up the surroundings

WATERater

Constructing an Energy Bar Chart

3. Decide whether Ech is involved In this case, you start with water and end

with water; particles are not rearranged to form new substances

So, ignore Ech for now.

Constructing an Energy Bar Chart

4. Assign values to Eph 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

Constructing an Energy Bar Chart

Assign values to Eph

Use two Eph bars before and after

WATER

Constructing an Energy Bar Chart

5. Choose bars for Eth depending on

temperature Use 2 bars for colder water and 4 bars for

warmer water

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

Constructing an Energy Bar Chart

WATER

Constructing an Energy Bar Chart

6. Now show energy transfer using arrows showing energy entering or leaving the system. Final situation has 2 more bars of E than

initial; 2 bars had to be added to the system

Label the arrow using the symbol of the transfer mechanism.

Constructing an Energy Bar Chart

4 BARS + 2 BARS 6 BARS

WATER

Q

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 using a temp/time graph and bar chart.

Initial & Final States

Choice of bars for Eth arbitrary, but keep consistent. We used 2 bars for room temp and usually use 1

bar for “cold” substances. Temp < 0˚C should be < 1 bar.

Account for Energy transfer

Energy must flow into system via heating