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How to Calculate Gibbs free energy

How to predict spontaneity

The Formula to calculate Gibbs free energy is:

There are a few ways to predict at what temperature range will the reaction be spontaneous by looking at the signs of entropy and enthalpy:

  • Delta G stands for Free energy, Delta H is Enthalpy, T is temperature, and Delta S is Entropy.
  • The temperature is usually given in Celsius but for the formula you have to convert it to Kelvin by adding 273K to the temperature.
  • Delta H is usually given in KJ/mol and if it is it needs to be converted to J/mol.
  • Delta S is given in J/(moles x Kelvin) and does not need to be converted.
  • Then plug in the values into the formula to get the free energy.

Introduction

Bibliography

How to predict spontaneity cont.

  • As the table shows, when the enthalpy is negative or the entropy is positive then the reaction will surely be spontaneous at some temperature range, but if the enthalpy is positive and the entropy is negative then it will not be spontaneous.

"Gibbs Free Energy." - Chemwiki. N.p., n.d. Web. 13 Apr. 2014.

"How Does Temperature Effect Gibbs Free Energy?" Yahoo! Answers. Yahoo!, n.d. Web.

13 Apr. 2014.

Tarin, Yalda, and Ryan Cheung. "What Is "free" Energy." - Chemwiki. N.p., n.d. Web.

10 Apr. 2014.

  • Gibbs free energy was first introduced by a Yale professor named Josiah Willard Gibbs in 1875.
  • Free energy is the difference between the Enthalpy(heat change) and the multiplication of the absolute temperature by the Entropy(disorder of the system).
  • The value of the free energy can tell us if the reaction is spontaneous or not. If Delta G (free energy) is positive then the reaction is non-spontaneous and if it is negative then it is spontaneous.
  • Temperature is also an important part in determining the free energy. Usually at higher temperatures the spontaneity of a reaction will be greater and at lower temperatures it will be less spontaneous. This is because as you increase the temperature, Delta G decreases making it more negative and thus more spontaneous.

Practice Problem

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Practice Problem

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Gibbs Free Energy

By: Shivani Nanda

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