Interactive Self-Study Module: First Law - Open Systems
Department of Chemical and Biological Engineering, University of Colorado Boulder 

This module uses screencasts and interactive simulations to explain the application of the first law of thermodynamics (energy balance) to open systems. These are systems with mass flow in and/or out. They may be at steady state (mass flow rate in = mass flow rate out), or they may be transient systems in which energy accumulates or is depleted from the system. The module provides example problems to allow the user to test themselves. We suggest reviewing the First Law: Closed Systems module before using the learning resources in the following order:

  1. Attempt to answer the multiple-choice ConcepTests before watching the screencasts or working with the simulations.
  2. Watch the screencasts that explain enthalpy, flow work, and the first law, and answer the questions within the screencasts.
  3. Use the two interactive simulations to further understand the behavior of the phase diagrams.
  4. Try to solve the two example problems before watching the solutions in the screencasts.
  5. Answer the ConcepTests.

Many real life processes are open systems and require energy and mass balances.

This module is intended for a thermodynamics course.

Before studying this module, you should:

After studying this module, you should be able to:
  1. Apply the first law for open systems in its differential equation form and its integrated form.
  2. Apply the first law (energy balance) to steady-state flow systems, including throttles, turbines, compressors, and pumps.
  3. Apply the unsteady-state first law to flow into or out of a tank.
  4. Understand how gas flowing into a tank does work on the tank contents.
  5. Explain the concept of flow work and why enthalpy is used for energy flowing into or out of a system.