Ideal Gases

• Pressure Law

  V = const

  n = const

  P = nR/V * T

  Therefore pressure is proportional to Temperature
• P*V = n*R*T


  P = pressure V = volume T = Temperature

  n = number of moles r = gas constant = 8.31
• P*V = N*k*T


  P = pressure V = volume N = number of particles k = Boltzmann's constant T = temperature
• Kinetic model pressure

  Pressure = the sum of all the forces acting on each other/ area
• Root mean squared 


  Square values 320^2 + 150^2 + 100^2 / 3

  Square root = 212 ms^-1

  
• 1/2 * m * c^2 = 3/2 * k * T


  m = mass of a particle of gas

  C = squared mean speed

  k = boltzman's constant 1.38 * 10^-23

  T = temperature
• Maxwell Boltzmann distribution

  Most particles have moderate speeds

  small proportion has a very high speed

  few particles have low speeds

  
• Describe the internal energy changes when temperature increases

  The kinetic energy increases and the potential energy increases
• Describe the internal energy changes when a fixed mass of a solid changes phase

  kinetic energy of the molecules are constant and the potential energy increases
• State 3 conclusions about the movement of gas molecules provided by observations of Brownian motion

  Smoke particles move in random linear motion

  Air particles are colliding with the smoke particles therefore are also moving in random linear motion

  Air particles are much smaller than smoke particles
• State Boyle's law in words (2)

  Pressure is inversely proportional to volume

  For a fixed mass at a constant volume and temperature
• Explain why the internal energy of a gas differs to that of its liquid phase. (2)

  Temperature in the gas phase is increased therefore the kinetic energy is greater in a gas

  Potential energy increases as energy must be supplied to change from liquid to gas
• State what is meant by the internal energy of a gas. (1)

  Sum of the randomly distributed kinetic and potential energies of the molecules
• Show how Boyle's law follows from PV=nRT (2)

  n and T remain constant

  R is a constant

  therefore P*V = constant
• Explain why there is a change in internal energy when a substance changes phase. (2)

  Temperature remains constant therefore the kinetic energy of the molecules remain constant

  Potential energy increases as work is done in moving the molecules apart
• State what is meant by a perfectly elastic collision. (1)

  Collision in which kinetic energy is conserved
• State 3 assumptions on the kinetic theory of gases:

  Particles move in random, rapid motion

  Collisions are perfectly elastic

  All internal energy is kinetic energy
• State two conditions which must be met for the gas to obey Boyle's Law. (2)

  Constant Temperature

  Fixed mass