What is Gibbs free energy? How is it useful?

The Gibbs free energy of a process is a measure of how readily that process will proceed on its own - a negative value means that the reaction is spontaneous, a positive value means that it is not, and a value of or very close to zero means that it's an equilibrium process.
 

It's equation is: G = H - TS
Where G is the Gibbs energy, H is the enthalpy change, T is the temperature that the process is at, and S is the entropy change.


Temperature here is in Kelvin, and a classic trick is to give you the temperature in celsius so you have to remember to account for it by adding 273.
Another easy pitfall is that since the entropy S is so much smaller than the enthalpy H, it will be in J K-1 Mol-1 - and H will be in kJ K-1 Mol-1​. So you need to put both values in the same units. Always remember to check that your units 'add up' correctly - this is just as important as your numbers.

Typically a question will ask you to find the enthalpy change, or entropy change of a reaction, then give you the value you don't have and ask you to comment on how likely the reaction is to occur through calculating this Gibbs energy. These questions are, when it comes down to it, just a bit of arithmetic. 

MM
Answered by Murdo M. Chemistry tutor

9248 Views

See similar Chemistry A Level tutors

Related Chemistry A Level answers

All answers ▸

Why does the first ionisation energy of atoms generally increase across a period?


State an explain the result of an increase in temperature on the following equilibria: N2 (g) + 02 (g) <-> 2 NO (g) (delta H = +180kJmol-1)


Palladium acts as a heterogeneous catalyst in the reaction between an alkene with hydrogen by providing an alternative reaction route. Describe the stages of this reaction route. (3 marks)


Lead (IV) oxide reacts with concentrated hydrochloric acid as follows: PbO2(s) + 4HCl(aq) -----> PbCl2(s) + Cl2(g) + 2H2O(l) What mass of lead chloride would be obtained from 37.2g of PbO2, and what mass of chlorine gas would be produced


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences