Energy Balances


In this chapter, we will introduce energy balances and relate them to chemical processes. Energy balances are very important in chemical and biological engineering since we often deal with large process equipment that either requires a lot of energy or releases a lot of energy. Knowing how much energy is going into our system and coming out of it is crucial. As chemical and biological engineers, we also deal with reactive systems, which are highly dependant on the energy of the system.

Learning Objectives

By the end of this chapter, you should be able to:

Identify relevant terms for energy balances for open and closed systems

Use thermodynamic data tables to identify enthalpy, internal energy, and other thermodynamic properties using system temperatures and pressures

Solve energy balance problems using thermodynamic data

Evaluate the cost of utilities in processes

Characterize energy changes in a system due to changes in temperature

Analyze energy balances on processes involving phase changes

Explain heats of reaction as well as endothermic and exothermic reactions

Determine the standard heat of reaction given other heats of reaction or heats of formation (Hess’s Law)

Analyze energy balances involving reactive systems


As you’re going through this chapter, here are some important terms for you to take note of:

  • isolated systems
  • closed systems
  • open systems
  • kinetic energy
  • potential energy
  • internal energy
  • heat
  • work
  • flow work
  • shaft work
  • First Law of Thermodynamics
  • steady-state open system energy balance
  • specific property
  • reference state
  • steam table
  • utilities
  • phase change
  • heat of vapourization
  • heat of fusion
  • heat capacity
  • process path
  • exothermic
  • endothermic
  • heat of reaction
  • heat of formation
  • Hess’s Law
  • formation reaction
  • standard specific heat of formation


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