ENERGY
IRP Binders & Log Books Name on log book Name(s) on binder Rubric clipped to contents page Log book(s) placed into binder Stack binders NEATLY (turn opposite directions) at designated location for your class.
Whiteboard Icy Hot Lab Conclusion Questions Group F #1 Group E #2 Group D 3 i Groups C & G #4 – Region A Group B #4 – Region B Groups 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 Monday We will discuss Energy Bar Charts on Monday Icy 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 Scale freezing point of water is set at 0oC boiling point of water is set at 100oC interval between them is divided into 100 parts Kelvin Scale absolute zero – theoretically the lowest possible temperature particles stop moving absolute zero = 0 K = - 273oC the 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 Temperature A Time (Energy)
Icy Hot Lab Changes in speed (motion) of particles Energy used to speed up particles of liquid Liquid only present Temperature B Time (Energy)
Icy Hot Lab Changes in physical arrangement of particles C Energy used to break attractions between particles of liquid Both Liquid & gas present C Temperature Time (Energy)
Icy Hot Lab “Report” Problem Question Prediction 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.
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 WATER Q 4 BARS + 2 BARS 6 BARS
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