1 / 8

Gibbs Free Energy

Gibbs Free Energy. Unit 3 - Thermodynamics. Will a Reaction Occur?. Both enthalpy and entropy are factors in determining on whether or not a reaction will occur.

abdalla
Download Presentation

Gibbs Free Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gibbs Free Energy Unit 3 - Thermodynamics

  2. Will a Reaction Occur? • Both enthalpy and entropy are factors in determining on whether or not a reaction will occur. • To determine whether or not a reaction will occur for sure is by using the relationship between these two values known as Gibbs Free Energy.

  3. “Free Energy” • Free energy is a measure of the work that can be obtained from the energy in a chemical reaction. • Spontaneous reactions are the only types of reactions that can actually do work because there is an energy transfer to the surroundings. • This energy transfer is what allows work to be done.

  4. Gibbs Free Energy Calculation • ΔG = ΔH - TΔS • where: • ΔG = free energy change (kJ or J) • ΔH = Enthalpy change (kJ or J) • T = Temperature (K) • ΔS = Entropy change (kJ/K or J/K) *Note: • The most important thing about this formula is that your UNITS match up • Make sure that: • Your temperature values are both in KELVIN • Your energy values are both in JOULES or KILOJOULES – as long as they are consistent!

  5. Using Gibbs Calculation • Once we know ΔG we can decide whether or not a reaction will be spontaneous: • i. If ΔG < 0  reaction is spontaneous • ii. if ΔG > 0  reaction is not spontaneous • iii. If ΔG = 0  reaction is at equilibrium (will be discussed more in a future unit). • In general, you will find most exothermic reactions to be spontaneous even if entropy is decreasing.

  6. Example: • Calculate the free energy change for the following reaction at 25˚C. • Will the reaction occur (will it be spontaneous)? NH3(g) + HCl(g) → NH4Cl(s) • ΔH = -176.0kJ • ΔS = -284.8J/K

  7. Another Way to Calculate Free Energy • Another way to calculate the change in free energy is by using our all too familiar equation: ΔG = ΣΔGproducts - ΣΔGreactants • The ΔG values are on our Thermochemical Data sheet. • Remember ΔG values must be multiplied by the balancing coefficients in this equation. • NOTE: The values given in the Table of Thermochemical Data are for temperatures of 25°C (298 K); therefore the values are really only valid for that temperature. If the reaction occurs at some other temperature, the formula ΔG = ΔH – TΔS should be used instead.

  8. Example: • Let's try the previous example again, this time using ΔG°f values from the Table of Thermochemical Data:

More Related