Lesson 5 Gas Pressure Kelvins

8/3/2019 Lesson 5 Gas Pressure Kelvins

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Do now!

• . Can you readthrough thework we did

last lesson?



Last lesson

• Understand that a substance can change statefrom solid to liquid by the process of melting

• Understand that a substance can change state

from liquid to gas by the process of evaporationor boiling

• Recall that particles in a liquid have a randommotion within a close-packed structure

• Recall that particles in a solid vibrate about fixedpositions within a close-packed regular structure

• Understand the significance of Brownian motion



Draw these sentences!

1. The particles in a solid are close packed.

2. The particles in a solid are in regular positions

vibrating around a fixed point.

3. The particles in a liquid are also close packed.

4. The particles in a liquid also vibrate and move

around randomly.

5. The particles in a gas are far apart.

6. The particles in a gas are moving very quickly.

7. For the same substance (e.g. water), the particles are the same size

in the solid, liquid or gaseous forms.

8. Mr Porter is the world’s best science teacher.



Solids

• Fixed shape

• Cannot flow

• Difficult to compress• Generally dense



Liquids

• Shape can change

• Can flow

• Not easy to compress• Generally dense



Gases

• Shape can change

• Can flow

• Easy to compress• Low density



Changes of state

• .



Brownian motion – Fat droplets in milk

• .

Einstein's Explanation of BrownianMotion http://www.practicalphysics.o

rg/fileLibrary/wmv/brownian_

Brownian

Motion

http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.html


http://www.practicalphysics.org/fileLibrary/wmv/brownian_motion.wmv


http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=24











.

• Brownian motion is the seeminglyrandom movement of particles suspendedin a fluid (i.e. a liquid or gas). It is due to

the instantaneous imbalance in thecombined forces exerted by collisions ofthe particle with the much smaller liquid

molecules surrounding it.



Today’s lesson

• Recall that molecules in a gas have arandom motion and that they exert a forceand hence a pressure on the walls of the

container• Understand that there is an absolute zero

of temperature which is – 273 oC

• Describe the kelvin scale of temperatureand be able to convert between the kelvinand Celsius scales



Pressure in a gas

What is origin of the pressure of a gas?

Volunteers please!





Pressure versus temperature (atconstant volume)

• .



P/T = constant

• P1 /T1 = P2 /T2



At -273°C, P = 0!!

• .



• .



.

• .



Kelvins

• .



Absolute/Kelvin temperature andCelsius

T (in Kelvin) = T (in degrees Celcius) + 273



Kelvin Temperature

The kelvin Temperature is proportional tothe average kinetic energy of the particlesin a substance.

Note that they arenot all travelling at

the same speed.



Temperature

The hotter the temperature, the faster theaverage speed of the particles

Note that they arenot all travelling at

the same speed.



Pressure and Volume atconstant temp?

• . Volunteers again?



pV = constant

• p1V1 = p2V2 (at constant temp)

Can youanswer thequestions

that Mr

Porter isgiving you?

Lesson 5 Gas Pressure Kelvins

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