Unit 5 Thermal Energy

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  • Created by: megan
  • Created on: 21-03-13 13:54
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  • Thermal Energy
    • Temperature
      • Kinetic theory- when energy is supplied to an object, the particles take up the energy as kinetic energy.
      • When the internal Kinetic energy has been removed, the temperature is at absolute zero.
        • Zero Degrees= 273.15 Kelvin.
    • Heat Transfer
      • More heat= More frequent collisons.Less heat =Slow moving molecules
      • The effect of the collisions means that energy is distributed.
    • Specific Heat Capacity
      • Transferring the same amount of heat energy to two different objects will increase their internal energy the same amount.
        • This will not necessarily cause the same rise in temperature
      • The effect that transferred heat energy has on the temperature of an object depends on three things : 1.the amount of heat energy transferred 2.The mass of the objects. 3. The specific heat capacity of the objects material.
      • Specific Heat capacity= the amount of energy needed to raise the temperature of 1 kg of a particular substance by 1K.
      • Materials have different specific heat capacity because their molecular structures are different.
      • dE= mc dT
    • Internal Energy
      • The average kinetic energy of the molecules in a material give it its temperature.
      • Each molecule will have potential energy by virtue of its position within the structure of the material. Or relation to other moleucles in the substance.
      • internal energy= kinetic energy of every molecule + Potential energy
      • The internal energy is randomly distributed across all the molecules
    • The maxwell boltzmann Distribution.
      • The values of the indicidual velocities of each molecule in a particular sample are varied.
        • As they all have the same mass, the kinetic energies are directly dependent on the speeds.
      • There are no molecules with zero energy. Only a few molecules have high energies.There is no maximum value for the energy a molecule can have.
      • The graph is for one specific temperature. as temperature changes the peak moves towards higher energies.
      • Root mean square speed is the speed associated with the average kinetic energy.
        • The RMS speed is found by squaring the individual speeds and finding the mean of the squares and then taknig the square root.
    • Molecular Kinetic Energy
      • The average kinetic energy of any molecule in a gaseous sample is proportianal to the absolute temperature of the gas
        • 1/2 <c ^2> = 3/2 kT
          • k= Boltzmann constant = 1.38 x 10 ^-23 JK ^1
        • At zero on the absolute scale of temperature the molecules will be stationary.
          • The mass cannot change so for their kinetic energy to be zero, at absolute zero their rms speed must also be zero.
    • Gas Laws
      • Boyles Law
        • For a constant mass of gas at a constant temperaure the pressure exerted by the gas is inversely proportional to the volume it occupies
      • Charles Law
        • For a constant mass of gas at a constant pressure, the volume occupied by the gas is proportional to its absolute temperature
      • The pressure law
        • For a constant mass of gas at a constant voume, the pressure exerted by the gas is proportional to its absolute temperature
    • Ideal Gases
      • The gas laws are not perfectly accurate.
        • An ideal Gas...
          • The molecules have zero size
          • The molecules are identical
          • The molecules collide with each other except during collisions
          • The molecules collide with each other without any loss of energy. in collisions which take zero time
          • There are enough  molecules so that statistics can be applioed
      • Assuming an ideal gas... PV-NkT
        • P= pressure. N= Number of molecules of gass
      • Assuming an ideal gas... pv=nRT
        • n- the number of moles of gas. R= univeral gass constant = 8.31 jkg^1 mol 61


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