UNIT 3 BELL RINGERS

Bell ringer 10/29

How could you determine the thickness of a stack if you weren't allowed to measure it ? Of a single coin?

Bell ringer 10/30

What could happen if atoms “stick” together?

Bell ringer 11/1

What is the matter with matter? Discuss A sample of matter is a balance between

the attractions holding the molecules together and the thermal motion that tends to tear them apart.

Dry ice

A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C).

sublimation -- as it breaks down, it turns directly into carbon dioxide gas rather than a liquid

To make dry ice, you start with a high-pressure container full of liquid carbon dioxide. When you release the liquid carbon dioxide from the tank, the expansion of the liquid and the high-speed evaporation of carbon dioxide gas cools the remainder of the liquid down to the freezing point, where it turns directly into a solid. If you have ever seen a carbon-dioxide fire extinguisher in action, you have seen this carbon-dioxide snow form in the nozzle. You compress the carbon-dioxide snow to create a block of dry ice.

Forces between atoms in a molecule

repulsion

attraction

d

F

r

Bell ringer 11/4

How does cooking noodles work? How do the molecules look?

Temperature (Celsius)

time

Demonstration

Thermal expansion of liquids Since the thermal

expansion of water or alcohol is reasonably linear, the height of the liquid in the thin capillary tube can be used as a measure of the "hotness" of the surroundings.).

20 C

Height change of Test tube 1

Change in height Test tube 2

temperature

Height change of Test tube 1

Change in height Test tube 2

temperature

Videos 4, 5, 6

https://www.youtube.com/watch?v=o7XR-HD_Kzo

https://www.youtube.com/watch?v=8PHGi5T1GVw

https://www.youtube.com/watch?v=AqDsAVPjgS4

Demo discussion

What happens when the thermometer is placed in surroundings that are "colder" than the alcohol in the reservoir? Then energy flows from the hotter

alcohol to the surroundings; the molecules in the bulb slow down and contract and the level of alcohol in the capillary tube falls.

The word "thermometer" comes from the words for hotness (thermos) and measure (meter)

What is the difference between heat and temperature? temperature -a measure of the

"hotness" of a substance or how fast the molecules are moving

heat -a measure of the energy transferred into or out of a system. This distinction is blurred because of the fact that we use these words to describe our sensation as well as objective measures.

Bell ringer 11/4

If you wanted to warm up the water in your wading pool, would it be better to use a teacup full of water at 100˚C or a bucket full of water at 50˚C?

https://www.youtube.com/watch?v=AqDsAVPjgS4

time (min)0.00 4.00 8.00 12.0

tem

p

(ÞC

)

0.00

10.0

20.0

30.0

40.0

50.0

What’s going on?

During heating, the energy supplied to the system tends to first overcome the interactions between the molecules (increasing interaction energy) before the overall collection of molecules begin to move around more rapidly (increasing kinetic energy). The minor fluctuations in temperature do occur as local regions become completely melted and the molecules begin to move more rapidly (get hotter).

Bell ringer 11/8

Explain what is going on

https://www.youtube.com/watch?v=BjULrwbQJzM

energy- 3 principals

1. Energy can be viewed as a substance-like quantity that can be stored in a physical system.

2. Energy can “flow” or be “transferred” from one system to another. When this happens, changes in the systems occur.

3. Energy maintains its identity after being transferred.

Type of energy- Ek

Kinetic energy, Ek – energy of motion. The quantity of kinetic energy stored by an object is related to both its mass and velocity. You instinctively recognize this

as you would rather catch barehanded a baseball thrown by your instructor than one thrown by a major league pitcher. Similarly, you wouldn’t mind if a softball landed on your toe, but would suddenly move if a shot put were heading that way.

 

Type of energy- Ei

Interaction energy, Ei – energy due to attractions between molecules. This is the energy account involved when phase changes occur.

Attractions can result in a decrease in the energy of a system.

Repulsions result in an increase of energy A solid possesses the lowest Ei; liquids possess more Ei since the molecules in a liquid

are freer to move than those in a solid; and a gas possesses the greatest amount of Ei since

the molecules in a gas have completely broken free from one another.

 

Type of energy- Ech

Chemical potential energy, Ech- energy due to attractions of atoms within molecules. These attractions are described as chemical bonds because they are considerably stronger than those between molecules and last much longer.

3 transfers

There are three energy transfer modes and these are described as gerunds to emphasize that they are processes rather than real things apart from energy.

They are working (W), heating (Q) and radiating (R).

These transfer modes operate to move energy between the system and the surroundings. It is very important to recognize that such energy transfers affect both the system and the surroundings. Energy doesn’t mysteriously appear or get lost.

Working

Working (referred to as work by the physicists as if it is something different from energy) is the way in which energy is transferred between macroscopic (large enough to be seen) objects that exert forces on one another. It is OK to calculate how much “work” one object does on another so long as you do not think that work is something an object stores.

 

heating

Heating (referred to as heat by the chemists) is the way in which energy is transferred by the collisions of countless microscopic objects. Energy is always transferred from the “hotter” object (one in which the molecules have greater Ek) to a colder one (one in which the molecules have lower Ek). If all the molecules have the same mass, then the “hotter” ones are moving faster than the “colder” ones. It’s OK to say that you heat an object – just not that the object stores heat.

Radiating

Radiating is the process in which energy is transferred by the absorption or emission of photons (particles of light). A light bulb filament can be heated to the point that it glows; this is the emission of photons that carry energy away from the filament. You can be warmed by light from the sun as the photons transfer energy to you.

²E

QW

R

Law of Conservation of Energy- state that the algebraic sum of these energy changes and transfers must add up to zero, accounting for all changes relative to the system.

KMT- kinetic molecular theory This is one of the really important theories in

chemistry. It accounts for the behavior of substances during all sorts of physical change. There are three key points: Matter is made of tiny particles that are in constant

random motion. These particles exert long-range attractions and

short-range repulsions on one another. Attractions bring about a reduction in the energy state (Ei ) of the system; repulsions bring about an increase in the energy.

A hotter sample is one whose molecules are moving (on average) faster than the molecules in a colder sample.

PHY- bell ringer text me

Text @ a2b45 To: (224)-231-5549

E sci.- 11/13

Text: @f31d8 To:224-231-5549

abstract

In this unit we learned about 3 types of energy. We learned their uses and transformations. Expressed this in energy graphs (line and bar and pie). We expressed molecules and their phase changes.

Abstract= 6th

Learned that temp change changes Ek. Ei is related to s l g. Adding heat to ice (0 degrees) causes melting before temp change. Conservation of Energy allows us our energy transformations.

4th abstract- unit 3

We went over how temperature relates to heat and how they are not the same. We compare 3 kinds of energy Ei Ek Ech. Energy transfer QRW. Compared with energy flow chart. Discussed the phase changes of water.