Particle Model of Matter 11. Gases – effect of work

Starter Describe and explain how the motion of molecules in a gas changes as the gas is heated using the key words: Organise your thoughts under three headings: Kinetic energy Internal energy Temperature.

Starter Describe and explain how the motion of molecules in a gas changes as the gas is heated using the key words: Kinetic energy As the gas is heated the kinetic energy of the gas molecules increases and they move faster. Internal energy As the gas is heated the internal energy of the gas increases. Temperature. As the average energy of the molecules has increased (the internal energy has increased) then the temperature will also have increased (you will not see a change of state here)

Today’s lesson goals: To explain the motion of molecules in a gas at different temperatures and pressures. To explain qualitatively the relationship between pressure and temperature

What is Pressure? 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆= 𝑭𝒐𝒓𝒄𝒆 𝑨𝒓𝒆𝒂 Year 9 … Equation: Measured in: What does it mean? 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆= 𝑭𝒐𝒓𝒄𝒆 𝑨𝒓𝒆𝒂 Newtons per square metre, N/m2 or Pascals, Pa The pressure will increase if the force is increased or the surface area is decreased. Lesson Aims:

What is pressure in a gas? Pressure of a gas is due to molecule collisions with the walls of the container. When the gas collides with the wall there is a force on the wall. There will be collisions over the whole surface area of the wall. So… because we have a force acting over an area, there is pressure. What happens to the force if the gas is hotter?

Experiment: linking pressure and temperature Experiment: linking pressure and temperature. Dry air is trapped in the flask with a fixed volume and its temperature is varied using the water bath. Diagram Results Pressure / kPa Temperature / oC 100 -73 150 27 200 127 250 227 300 327

Conclusion The graph is a straight line which cuts the temperature axis at -273 oC. This is the lowest possible temperature and is called absolute zero. It is at zero Kelvin. The graph shows that at a constant volume; pressure and temperature are directly proportional.

What happens when the temperature rises? At a higher temperature the molecules have more energy. They move faster and will collide more with the walls of the container. As the molecules are moving faster the collisions will have a greater force. There will be a greater force over the same surface area (if the volume does not change) so the pressure will go up. Lesson Aims:

What will happen in these situations What will happen in these situations? Explain these situations to your partner using the kinetic theory.

What about when it gets really cold? https://www.youtube.com/watch?v=ZvrJgGhnmJo Watch the clip, why does the volume change here?

Assessment homework kinetic theory and gas pressure.docx Answer all the questions on the sheet Assessment homework kinetic theory and gas pressure.docx