Question

 

Describe the temperature relationship between a solute and solvent .How does this relationship differ from a gaseous solute and solvent ? Why do you think this is

How can we determine if a compound is IR active ? What types of compounds are considered IR active ? Give an example of one of these compounds and an example of compounds are not IR active

Answer 1

Temperature dependence of solubility:-

Generally, solubility of solute increases on increasing temperature but this is not always true as this depends on thermodynamics of that reaction.

If reaction is endothermic, then on increasing temperature – reaction will shift forward (according to Le Chatlier's Principle) and solubility will increase on increasing temperature.

If reaction is exothermic, then on increasing temperature – reaction will shift backward (according to Le Chatlier's Principle) and solubility will decrease on increasing temperature.

CASE OF GASES:-

In case of gases, solubility always decreases on increasing temperature as heating a solution of a gas enables the particles of gas to move more freely between the solution and the gas phase. Thus solubility always of gases always decreases on increasing temperature.

INFRARED ACTIVITY:-

The best way to consider IR activity of vibrations is to study symmetry and molecular point groups. An IR active vibrational mode has the same irreducible representation as the x, y, or z operators. This stems from the fact that the matrix element for the IR transition is the dipole operator.

For Example- H2O molecule is a non-linear molecule due to the uneven distribution of the electron density. O2 is more electronegative than H2 and carries a negative charge, while H has a partial positive charge. The total degrees of freedom for H2O will be 3(3)-6 = 9-6 = 3 degrees of freedom which correspond to the following stretching and bending vibrations

Some structures are infrared inactive because of absence of vibrations that result in IR activity. relatively neutral bonds ( C-C , C-H , C=C ,) suffer large changes in polarisability during a vibration, though this is less easy to visualise.