Question

Draw a reaction coordinate for both an exothermic and an endothermic reaction. Be sure to label the axes, the average energies of the reactants and the products, then energy releasd or absorbed, and the activation energy.

Solute Solubiltity

0 degrees C 50 degrees C 100 degrees C

lead (ii) bromide PbBr2 0.455 1.94 4.75

silver sulfate Ag2SO4 0.573 1.08 1.41

sodium chloride NaCl 35.7 37.0 39.8

silver nitrate AgNO3 122 455 952

cesium chloride CsCl 161.4 218.5 270.4

copper (ii) sulfate CuSo4 14.3 33.3 75.4

Answer 1

Solubility is the maximum amount of solvent that is soluble to a given amount of solvent at a particular temperature.

It increase in temperature usually increases the solubility due to the increase in the rate of the forward reaction where the solubility increases.

Solubility depends on two main factors,

1) how strong ionic attractions are in the solid.

2) how well solvated each ion is when it's dissolved in water.

Using just the ionic model, this gives rise (for group 1 halides atleast and so is probably at least representative of these compounds) to a pattern whereby ions of similar size form insoluble solids, whereas ions of different size form more soluble compounds.

Halide anions having an extra electron, and so are always quite large (Cl^-: 1.67 A, Br^-: 1.82A, I^-: 2.06A), so their least soluble compounds would be expected with large cations, Pb2+ is large (1.33A) being low in the periodic table, and Ag+ is large too (1.15A)because it too is quite low and has only lost 1 outer electron. This is a possible explanation as to why these compounds are insoluble whilst things like NaCl are very soluble (because Na+ is a small cation (1.02A). Nitrates are sulphates are larger anions and with larger ions like silver are only sparingly soluble. For eg;- silver suphate, is only sparingly soluble due to the inefective packing of these ions. CuSO4 is more or less soluble and thus the Cu(2+) and the sulphate are best matched and the lattice can be easily broken with the sovation.Cu(2+) radius is 0.73 Angstroms and thus the difference is pronounced in the matter of size between cation and the Sulphate (being large anion).

The increase of the temperature usually increases the solubility of any particular salt. The temperature increases the internal energy of the molecule making the internal bonds and linkages in the lattice weaker and thus easily soluble in the solution phase.The higher temperature usually increases the rate of the forward reaction of the salts being dissociated to their constuituted ions.All the salts show an increase on their solubilities and the increase is more pronounced on the AgNO3 and in CsCl. AgNO3 is significantly soluble in water and the solubility increases manifold in increasing temperature due to the pronounced differences in the lattice. NaCL on the other hand the increase is smooth thereby effectively suggests that the Cl- ions being more rigid in the lattice rather than SO4(2-) or NO3(2-). They can leave out few O atoms and thus can involve in major readjustemnts in the lattice structure wit the cation and thus showed more pronounced trend.