Do now!

Can you read through the work we did last lesson?

Last lesson

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

• Understand that a substance can change state from liquid to gas by the process of evaporation or boiling

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

• Recall that particles in a solid vibrate about fixed positions 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 Brownian Motion

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

Brownian Motion

• Brownian motion is the seemingly random movement of particles suspended in a fluid (i.e. a liquid or gas). It is due to the instantaneous imbalance in the combined forces exerted by collisions of the particle with the much smaller liquid molecules surrounding it.

Today’s lesson

• Recall that molecules in a gas have a random motion and that they exert a force and 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 temperature and be able to convert between the kelvin and Celsius scales

Pressure in a gas

What is origin of the pressure of a gas?

Volunteers please!

Pressure in a gas

Collisions of the gas particles with the side of a container give rise to a force, which averaged of billions of collisions per second macroscopically is measured as the pressure of the gas

Pressure versus temperature (at constant volume)

P/T = constant

• P1/T1 = P2/T2

At -273°C, P = 0!!

Kelvins

Absolute/Kelvin temperature and Celsius

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

Kelvin Temperature

The kelvin Temperature is proportional to the average kinetic energy of the particles in a substance.

Note that they are not all travelling at the same speed.

Temperature

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

Note that they are not all travelling at the same speed.

Pressure and Volume at constant temp?

Volunteers again?

pV = constant

• p1V1 = p2V2 (at constant temp)

Can you answer the questions

that Mr Porter is

giving you?