2. Kinetic Theory and Gas Pressure Objectives (d) define the term pressure and use the kinetic model to explain the pressure exerted by gases; (i) state the basic assumptions of the kinetic theory of gases;

3. Outcomes ALL MUST Be able to define pressure. Be able to use the kinetic model to describe pressure. MOST SHOULD Be able to state the basic assumptions of the kinetic theory of gases. Be able to use the kinetic model to explain the pressure exerted by gases. Be able to select and use the equation p=1/3ρv 2 SOME COULD Be able to derive the equation p=1/3ρv 2

4. Pressure P (Pa) = F (N) / A (m 2 )

6. The Kinetic Theory of Gases Thermodynamics Question (We do not have enough particles here to be realistic but it will illustrate the point!) 6 particles have the following speeds: 600, 650, 650, 700, 725, 750ms -1. Determine the most probable speed c p, the mean speed and the root mean square speed c rms.

7. The Kinetic Theory of Gases Thermodynamics The most probable speed c p = 650ms -1 as there are more particles going at that speed than any other. 6 particles have the following speeds: 600, 650, 650, 700, 725, 750ms -1.

8. The Kinetic Theory of Gases Thermodynamics 6 particles have the following speeds: 600, 650, 650, 700, 725, 750ms -1.

9. The Kinetic Theory of Gases Thermodynamics 6 particles have the following speeds: 600, 650, 650, 700, 725, 750ms -1.

10. Assumptions of the kinetic theory of an IDEAL GAS. 11A Gas consists of particles called molecules. 22The molecules are in constant random motion. As many travelling in one direction as any other. The centre of mass of the gas is at rest. 3Intermolecular forces are negligible. 4The duration of collisions between molecules is negligible. 5Molecules move with constant velocity in between collisions. 66The volume of gas molecules is negligible compared with the volume of the gas. 7All collisions are totally elastic. 8Newtonian mechanics can be applied to the collisions.

11. The Kinetic Theory of Gases Thermodynamics If these assumptions are correct, we should be able to prove the equation of state for an ideal gas from these assumptions! WOW!

12. The Kinetic Theory of Gases Thermodynamics Consider the change in momentum as the particle hits the wall

13. The Kinetic Theory of Gases Thermodynamics So

14. Outcomes ALL MUST Be able to define pressure. Be able to use the kinetic model to describe pressure. MOST SHOULD Be able to state the basic assumptions of the kinetic theory of gases. Be able to use the kinetic model to explain the pressure exerted by gases. Be able to select and use the equation p=1/3ρv 2 SOME COULD Be able to derive the equation p=1/3ρv 2