# Unit 5 Thermal Energy

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• Created by: megan
• Created on: 21-03-13 13:54
• 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