What is ChemReaX?

ChemReaX™ is a free web app for modeling and simulating basic chemical reactions. The software is intended for chemistry students and their teachers at the undergraduate and high school (AP/IB) levels. The ChemReaX simluation platform makes it easy to create sophisticated virtual labs in general chemistry and physical chemistry courses.

ChemReaX can be used to experiment with chemical thermodynamics, reaction equilibria, kinetics, and acid-base titration. It includes thermodynamic properties for over 1200 chemical species, allowing users to construct a virtually unlimited variety of chemical reactions. Or users can choose from over 80 predefined reactions. ChemReaX simulates a given reaction from initial conditions to a final equilibrium state, and accurately models the effects of concentrations, temperature and pressure. It comes with a detailed user guide, tutorials and several ready-to-use virtual lab exercises.

Questions that can be answered include: Is it possible for a reaction to occur? In which direction will the reaction proceed given an initial state? Is the reaction spontaneous? What is the final equilibrium state?  What if there is a limiting reactant? How does the reaction respond to changes in temperature and initial concentrations of reactants/products? How does the reaction respond to pressure changes at equilibrium? How fast does a reaction proceed and how do the reactant/product concentrations change over time?

ChemReax is listed in the National Science Digital Library, MERLOT, EdSurge and LearnPlatform databases as an online chemistry education tool, and is also available through the LibreTexts open-access textbook project.

How is ChemReaX typically used?

ChemReaX can be used as a virtual lab or testbench to model and simulate a nearly unlimited variety of chemical reactions. The 1200+ chemical species in the ChemReaX database can be combined together as reactants or products in a chemical reaction, covering most reactions of interest to chemistry students and teachers. Reactants and products are selected using the searchable drop-down lists. The user can either balance the equation and have ChemReaX verify its validity, or allow ChemReaX to automatically balance it. The user then enters the initial concentrations of the reactants and products. Temperature, pressure factor and reaction rate parameters are additional variables that can be set by the user. When the "Run the Reaction" button is pressed, ChemReaX performs equilibrium calculations and then simulates the reaction until a final steady state is reached. Results are provided in tabular and graphical forms.

Some typical applications:

  • Run virtual "experiments" and collect data for lab exercises on any number of chemical reactions:
    • Put together any reaction of interest using the 1200+ chemical species in the database. Currently up to to three reactants and three products can be chosen. This allows for a nearly unlimited number of reactions to be studied.
    • Vary initial concentrations or partial pressures of all reactants/products, as well as temperature -- and “run” each reaction under selected conditions.
    • Vary the pressure factor relative to a baseline to see the effect of pressure changes when a reaction is at equilibrium.
    • Model the reaction rate as an additional option to study reaction kinetics and thermodynamics in a single framework.
    • Data collected from the virtual experiments may include final concentrations of all substances, overall free energy change, overall standard enthalpy/entropy changes, reaction kinetics, and other details.
    • Run simulated titrations to study acid-base interactions. Choose from a large selection of strong/weak acids and bases as titrands, and vary the titrand and titrant volumes and concentrations.
  • Predict the outcomes of any reaction and compare with ChemReaX results:
    • Predict the direction of the reaction from a given initial state at a given temperature -- and then compare with simulation results from ChemReaX.
    • Hand-calculate the equilibrium state and final concentrations (including the effect of any limiting reactants) -- and then compare with simulation results from ChemReaX.
    • Predict the effect of effect of variations in temperature, pressure and initial concentrations on the final equilibrium state per Le Chatelier's principle -- and then compare with simulation results from ChemReaX.
    • Predict the result of an acid-base titration -- and then compare with simulation results from ChemReaX.
  • Apply Hess's law to break up a complex equation into a set of simpler additive equations for thermodynamic calculations. Get the free energy change (∆G) for each simpler equation from ChemReaX and compute the overall free energy change, and then compare with ChemReaX results for the single complex equation.
  • Conveniently get thermodynamic properties (standard molar enthalpy of formation and entropy at a specified temperature) for any of the 1200+ species in the database for use outside of ChemReaX. This is the largest free online database of chemical thermodynamic properties as a function of temperature.
  • Automatically perform stoichiometric balancing of chemical reactions.
  • Check the validity of a chemical equation by verifying that mass and charge are conserved.

What is unique about ChemReaX?

    • ChemReaX allows users to construct a virtually unlimited variety of chemical reactions using the 1200+ species in the internal database, and automatically verifies the validity of the equations and/or automatically balances the equations. It also comes with over 80 pre-defined reactions that can be quickly selected under 10 different categories.
    • Simulates a given reaction from the initial conditions until it reaches a final equilibrium state using an event-driven simulation algorithm, and accurately generates the final concentrations of all reaction components based on initial concentrations (or partial pressures) and temperature.
    • Evaluates the effects of pressure changes at equilibrium and produces the pressure-adjusted final compositions of products and reactants.
    • Simulates reaction kinetics utilizing a reaction-rate model (with user-defined parameters) based on a time-driven simulation algorithm, and displays the reactant/product compositions graphically as a function of time.
    • Simulates acid-base titrations utilizing the same underlying simulation technology used for general reactions.
    • Puts a powerful modeling and simulation capability in the hands of chemistry students and teachers. It is not an animation tool, but a real simulation tool -- similar to tools used in industry -- that can help with serious scientific study and inquiry and enable an investigative/experimental approach to learning chemistry.
    • Provides the largest free online database of chemical thermodynamic properties as a function of temperature.
    • ChemReaX is web-based and hosted on the cloud. There is nothing to install on the user's computer and any web browser will do for accessing the tool.

Is ChemReaX free to use?

Yes, ChemReaX is absolutely free at present. A basic set of functions and capabilities will always remain free for all students and teachers to access from anywhere in the world.

How can users participate in the further development and evolution of ChemReaX?

As you use this software tool, please let us know what you like, what you don't like, and what features should be added or improved for a better learning experience. We absolutely need your input and help to make the idea of teaching/learning science by simulation a reality. We especially want to hear from you if you are a teacher/professor and are interested in incorporating this technology into a chemistry course that you are teaching. The technology is here, let us work together to perfect it. Please contact us at info@sciencebysimulation.com .

What are the sources of the theory and data used in ChemReaX?

  1. Pauling, L. 1988. General Chemistry. New York: Dover Publications.

  2. Atkins, P. and De Paula, J. 2014. Physical Chemistry: Thermodynamics, Structure, and Change. New York: W.H. Freeman & Co.

  3. DeVoe, H. 2014. Thermodynamics and Chemistry. Department of Chemistry and Biochemistry, University of Maryland.

  4. Rosenberg, J.L., Epstein, L.M., and Krieger, P.J. 2013. College Chemistry. Schaum's Outline Series. New York: McGraw Hill Education.

  5. Cox, J. D., Wagman, D. D., and Medvedev, V. A. 1989. CODATA Key Values for Thermodynamics. New York: Hemisphere Publishing Corp.

  6. McBride, B.J., Gordon, S., and Reno, M.A. 1993. Coefficients for Calculating Thermodynamic and Transport Properties of Individual Species. NASA Technical Memorandum 4513.

  7. Goldberg, R.N., Kishore, N., and Lennen, R.M. 2002. Thermodynamic Quantities for the Ionization Reactions of Buffers. J. Phys. Chem. Ref. Data, Vol. 31, No. 2.

  8. Dill, D. 2008. Notes on General Chemistry . Department of Chemistry, Boston University.

  9. Higham, D.J. 2008. Modeling and Simulating Chemical Reactions. SIAM REVIEW, Vol. 50, No. 2.

  10. CRC. 2004. CRC Handbook of Chemistry and Physics, 84th Edition.

Copyright (C) 2015-2017 by ScienceBySimulation. All rights Reserved.
Contact us at