Mod 3: Thermodynamics and Waves

• U=Q-W where U is CHANGE in heat, Q is heat and W is work done by a system
• Conservation of thermal energy equation:

  mcΔT(hot) = mcΔT(cold)

  Where the ΔT is final-initial temperature
• Q=mcΔT is the equation used to find the amount of work done to change the heat in the system. Where "c" is the specific heat capacity
• W is positive if work is done BY the system
• Latent heat of fusion: The amount of energy needed to change the state of a substance without changing its temperature.
• Zeroeth law of Thermodynamics: if an object is in thermal equilibrium with an object which is in thermal equilibrium with another, they are all in thermal equilibrium with eachother.
• First law of thermodynamics

  
• Second law of Thermodynamics: The entropy of a system increases with time.
• Third law of Thermodynamics: The entropy of the universe is increasing and the temperature of a system will continue to approach a constant 0.
• thermal equilibrium formula:

  • mcΔ(x-Tfinal)(hot) = mcΔ(Tfinal-x)(cold)
• Latent heat of fusion (melting): The particles in the solid when heat is added gain internal energy. Once the particles break close bonds, instead of increasing temperature, potential energy is increased, reducing intermolecular forces. All the supplied energy is utilised to reduce such forces. The same amount of energy used to turn solidinto liquid is used to turn liquid into solid.
• Latent heat of vaporisation (boiling): This is much higher than changing a solid into liquid since intermolecular bonds must first be broken. The temperature will not rise until ALL of the material in liquid state has turned into gas. The same amount of energy used to convert liquid to gas is used to convert gas to liquid.
• Specific heat capacity


  The amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C
• Latent heat equation for ONLY change in state:

  Q=mL

  Q=energy

  L= Latent heat

  m= mass
• Latent heat equation for change in state AND temperature:

  Q=mcΔT+mL
• Specific heat capacity:


  Q=mcΔT
• Heat transfers can be done through COnduction, Convection, and radiation
• Convection is achieved through the movement of fluid. Warmer fluids would rise/expand. The flow of particles produce convection currents.
• Radiation is achieved through transfer of heat through electromagnetic waves. They do not need a medium. It can be reflected transmitted, or absorbed.
• Conduction is achieved through contact between two objects.
• Thermal conductivity equation: 


  Q/t = kAΔT/d

  Q/t = energy over time

  k = Thermal conductivity constant

  A = cross-sectional area of contact

  d = distance/thickness of the objects