HEAT-AND-HEAT-ENGINES

• Heat:

  • Transferred from an object with high temperature to an object where temperature is lower.
  • The process is said to be a spontaneous until the temperature of the two objects is in equilibrium or equal.
  • To find out how much work is done to transfer heat energy, how much heat is dissipated out of the system, and how much energy is needed to increase the internal energy of the system we use the equation: INTERNAL ENERGY EQUALS HEAT MINUS WORK (∆U = Q – W). All of these quantities are measured in Joules/J
• Indication of the Symbols:

  • ∆U = Internal energy
  • Q = Heat
  • W = Work
  • J = Joules
• In this equation ( ∆U = Q – W), we have the following conventions:

  1. Q is positive if the heat ADDED to the system
  2. W is positive if work is done BY the system
  3. Q is negative if heat LEAVES the system
  4. W is negative if work is done ON the system
• Second Law of Thermodynamics:

  • Heat will never by itself flow from a system of lower temperature to a system of higher temperature.
• What is the solution to this question:

  • FIRST: Identify the Given; Q = unknown , ∆U = 80 J, W = -120 J
  • SECOND: Identify the Convection; which is "Q is positive if the heat added to the system" due to the keyword "The internal energy INCREASES"
  • THIRD: Identify the equation and Solve;
  • Q = ∆U + W, Q = 80 J + (-120 J), Q = -40 J

  
• Heat pump:

  • An instrument used to reverse the natural flow of heat or spontaneous process of heat transfer into a non-spontaneous process by absorbing heat from a cold space and releasing it to a warmer one.