What Is Entropy?

Entropy is covered in the AHL part of the course: Topic 15.1 in the energetics / thermochemistry unit. The entropy change (symbol = S) in a chemical reaction is determined by as follows: total entropy change = total entropy of products – total entropy of the reactants You will have probably been taught that entropy is a measure of disorder. Order goes to disorder. The universe is expanding (and therefore getting more disordered). Liquid water has a greater entropy than solid water (ice) ...

Greek Claws and Entropy

Yesterdays post focused on chelating agents. These are spieceies that can form more than one dative co-ordinate bond with transition metal ions. I ended writing that chelation forms very stable complex ions but why does chelation form stable complexes? Well, the answer is quite deep routed in entropy. Essentially, the reactions produce a very large change in entropy. The enthalpy change is negligible which means that the Gibbs free energy becomes very negative (and very feasible or very spontaneous). This is quite hard ...

Book Review – From Here To Eternity

  ‘From Here To Eternity’ – written by Sean Carroll (ISBN-10: 0525951334) is a really great read and I would thoroughly recommend it. The book is quite ‘Physicsy’ (if there is a word) but deals with some interesting Chemistry ideas as well, such as….. ….. entropy and the reason why it is increasing (as opposed to decreasing) and why it seems to flow in one direction, much like time. You can read a review on the author here: http://www.ted.com/speakers/sean_carroll.html

Heat flow

Heat is a bit like time - it only flows in one direction. From heat's point of view it flows from hot to cold. Here is a dead simple experiment to show this - and it contains some good IB Chemistry as well. Get an ice cube. Soak a piece of string in water. Lay the end of the string on the ice cube and sprinkle some salt onto the string. The string will freeze onto the ice cube. But why? Well, ...

Hydrogen from Water and Carbon?

If we could easily produce Hydrogen, one of the many stumbling blocks to producing a cheap, mass produced hydrogen cell would be removed. We would have all the fuel we need.   The reaction below seems to give us all the Hydrogen we could possibly need. Why is it therefore not used? (and it is not because of the CO2!) H2O(g) + C(s) → H2(g) + CO(g) We can answer the question using Gibbs Free Energy: H2O(g) C(s) H2(g) CO(g)  ΔHfo/ kJ mol-1  -241.8  0  0  -110.5  So/ JK-1 mol-1  188.7  5.7  130.6  197.6 See if you can calculate ΔG for the ...