Pressure

• Explain the pressure of a gas in terms of the motion of particles.

  The particles move in random directions. When they collide with the walls of a container they exert a force which acts at a right angle to the container. This causes pressure.
• State the equation used to calculate pressure. Give appropriate units.

  Pressure (Pa) = Force (N) / Area (m^2)

  P = F/A
• What factors affects the average kinetic energy of gas molecules?

  The temperature of the gas. The higher the temperature, the higher the average kinetic energy of he molecules.
• What effect does increasing temperature have on the pressure of a gas when held at constant volume?

  Gas pressure will increase as the temperature increases.
• Why does pressure increase as temperature increases (at a constant volume)?

  Kinetic energy of molecules increases. Collisions between molecules becomes more frequent. Greater rate of change of momentum. Greater force and therefore pressure.
• If gas A is at a low pressure, and gas B is at a high pressure, what can be said about the rate of collisions in each gas?


  There are more collisions per second in gas A than in gas B. The rate of collisions is higher in A.
• Describe the force that the pressure of a gas exerts on the walls of its container.

  The net force acts at right-angles to each surface of the container. The force increases as pressure increases.
• Explain how increasing the volume of a gas results in a decrease of pressure.

  Molecules become more spread out so rate of collision decreases. Rate of change momentum decreases, and so force exerted on container decreases, resulting in a lower pressure.
• What is the unit used for pressure?

  Pascal (Pa).
• What increases when you do work on a gas?

  The internal energy of the gas. This can also lead to an increase o temperature.
• How do you convert between degree celsius and kelvin?

  *C -> Kelvin = +273

  Kelvin -> *C = -273
• What is absolute zero?

  -273*C.

  Particles have no kinetic energy and do not move.
• What equation can be used to calculate the pressure/volume for a gas for which the mass is fixed and temperature is constant?

  P1 x V1 = P2 X V2