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First Law of Thermodynamics quiz

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  • What does the first law of thermodynamics state about energy?
    It states that energy cannot be created or destroyed, only transferred between a system and its surroundings.
  • In thermodynamics, what is defined as the 'system'?
    The system is the substance or chemical reaction being studied or analyzed.
  • What are the 'surroundings' in a thermodynamic context?
    The surroundings include everything outside the system, such as the container, the environment, and the universe.
  • How can energy be transferred between a system and its surroundings?
    Energy can be transferred as heat (q) or work (w).
  • What does the variable 'q' represent in thermodynamics?
    'q' represents heat, which is the flow of thermal energy from a higher temperature object to a lower temperature object.
  • What does the variable 'w' represent in thermodynamics?
    'w' represents work, which is the movement of reacting molecules against gravity or an opposing force.
  • When is the sign of 'q' positive for a system?
    The sign of 'q' is positive when the system gains, absorbs, or takes in heat.
  • When is the sign of 'q' negative for a system?
    The sign of 'q' is negative when the system loses, evolves, releases, or gives off heat.
  • What determines the direction of heat flow between two objects?
    Heat always flows from the hotter object to the colder object.
  • When is the sign of 'w' negative for a system?
    The sign of 'w' is negative when the system does work on the surroundings.
  • When is the sign of 'w' positive for a system?
    The sign of 'w' is positive when the surroundings do work on the system.
  • If a gas in a container pushes up a piston, what is the sign of 'w' for the gas?
    The sign of 'w' is negative because the system (gas) is doing work on the surroundings (piston).
  • If a piston is pushed down onto a gas by an outside force, what is the sign of 'w' for the gas?
    The sign of 'w' is positive because the surroundings are doing work on the system (gas).
  • Why can't energy be created or destroyed according to the first law of thermodynamics?
    Because energy can only change forms or be transferred, but its total amount remains constant.
  • How do the signs of 'q' and 'w' help in thermodynamic analysis?
    They indicate whether the system is gaining or losing energy through heat or work, which helps analyze energy changes in processes.