Introduction to the First Law of Thermodynamics - Closed Systems: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • The first law is an energy balance. For a closed system ΔU + ΔEK + ΔEP = Q + W.
  • No mass flow into or out of a closed system.
  • Work is done when a gas expands against an external force in a piston-cylinder.
  • Q = 0 for an adiabatic process.
  • W = 0 if there are no moving parts or electrical currents at boundary.
  • Internal energy does not depend on pressure for an ideal gas.
  • For liquids and solids, internal energy does not depend significantly on pressure.
From studying this module, you should now be able to:
  • Perform energy balances around a closed system.
  • Simplify energy balance for a closed system to remove terms that are not important.
  • Determine final states of various processes (e.g., constant pressure, adiabatic, constant volume, and constant temperature).
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder