MODULE 4

• Heat


  Energy in transit
• System


  A well-defined space, group of atoms, particles, or objects which is the focus of an observer
• Internal Energy


  The energy possessed by a substance at the particle level
• Work


  The product of force and displacement
• Surrounding


  Anything around the focus of the observation
• Observing How Heat Causes Work

  1. Put 1 cup of water in a pot and cover it with the lid

  2. Bring the water to a boil

  3. Observe what happens
• As the water is heated, the energy of the molecules increases that causes them to move faster
• Due to the increase in molecular energy, a phase change occurs, turning water into steam
• Since steam carries much energy as compared to the outside environment, this will push the lid upwards
• 1st Law of Thermodynamics


  Energy can neither be created nor destroyed, it is only converted from one form to another
• Heat only flows from high temperature to low temperature
• Change in internal energy (ΔU)

  ΔU = Q - W
• If work is done by the system, the internal energy decreases, since the energy is converted from heat to mechanical energy
• If work is done on the system, the internal energy increases
• Solving for change in internal energy

  1. Given: Q = +3000 J, W = +1000 J

  2. ΔU = Q - W

  3. ΔU = 3000 J - 1000 J

  4. ΔU = 2000 J
• As heat is added to the system


  The temperature of the system increases, caused by the increase in the average kinetic energy of the system
• If the internal energy decreases

  Work is done by the system
• If the internal energy increases

  Work is done on the system, provided that there is no addition nor removal of heat