The First Law of Thermodynamics

• What is the First Law of Thermodynamics based on?

  Principle of conservation of energy
• How is the internal energy of a system increased?

  By heating or work done on it
• What happens to internal energy when work is done on the system?

  It increases
• What is one way internal energy can be decreased?

  When work is done by the system
• What occurs when thermal energy is transferred away from the system?

  Internal energy of the system decreases
• What is mechanical work defined as?

  Distance covered against a force
• Why is work done important in thermodynamics?

  It relates to gas expansion or compression
• What happens when a gas expands?

  Work is done by the gas on surroundings
• What occurs when a gas is compressed?

  Work is done on the gas by surroundings
• What is a common scenario for work done on a gas?

  A gas in a container with a piston
• How does a piston affect the gas in a container?

  Piston can compress or expand the gas
• What happens when the piston moves down?

  Space occupied by gas is compressed
• What occurs if the system is insulated during compression?

  Work increases the internal energy of gas
• What happens to the average kinetic energy of particles when internal energy increases?

  Particles have greater average kinetic energy
• What happens when the piston moves up?

  Space occupied by gas expands
• What occurs if the system is insulated during expansion?

  Work decreases the internal energy of gas
• What happens to the average kinetic energy of particles when internal energy decreases?

  Particles have lower average kinetic energy
• What should you understand qualitatively about the First Law of Thermodynamics?

  • Causes of change in internal energy
  • Explanation using conservation of energy
• Do you need to learn any equations for the First Law of Thermodynamics?

  No, only qualitative understanding is needed