The Mandatory Labs / Skills: Topic 5.1, A Calorimetry Experiment for an Enthalpy of Reaction

Over the last couple of months I have posted some ideas of lab work for you to help with the mandatory labs or mandatory skills that the IB has stipulated are carried out over the duration of the IB course. So far we have looked at labs for deducing the empirical formula of compounds, examples of titration labs and labs to calculate the Mr of a substance using the ideal gas equation. This months post will take up where the others have ...

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 ...

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 ...

Exothermic and Endothermic Change

Students love new trends and we have one just starting in our school that has origionated from some lessons (not mine!) on endo and exothermic reactions. The trend is handwarmers ...... and it's not even that cold! There are two types of heat changes associated with chemical reactions. Exothermic reactions (ones that give off heat energy) and endothermic reactions (those that take in heat enery). An example of an exothermic reaction would the thermite reaction:   This reaction evolves (gives off) large amounts of heat ...