JEE Chemistry Physical Chemistry Mixed Topics Notes Set 01

Chemical Equilibrium

1. Le Chatelier: a system at equilibrium shifts to oppose any change in concentration, pressure or temperature.
2. Increase of temperature favours the endothermic direction. Increase of pressure favours the side with fewer gas moles.
3. \(K_p = K_c(RT)^{\Delta n_g}\). Only temperature changes the value of K: an exothermic reaction has a larger K at lower temperature.
4. Partial pressure = mole fraction multiplied by the total pressure.
5. Degree of dissociation from vapour density: \(\alpha = \dfrac{D_T - D_0}{(n-1)D_0}\), where n is the number of product moles from one mole of reactant.

Ionic Equilibrium

1. Buffer: \(pH = pK_a + \log\dfrac{[\text{salt}]}{[\text{acid}]}\).
2. Salt of a weak acid with a strong base is basic. Salt of a strong acid with a weak base is acidic. Strong with strong is neutral.
3. \(K_w\) increases with temperature, so the neutral pH is below 7 above 25 degrees C.
4. Indicator choice: use the one whose range includes the pH at the equivalence point. Phenolphthalein suits a weak acid with a strong base.

States of Matter

Real gases approach ideal behaviour at low pressure and high temperature. Graham's law: the rate of diffusion is proportional to \(\dfrac{1}{\sqrt{M}}\), so lighter gases diffuse faster. A plot of PV against P is a horizontal line for an ideal gas.

Solutions

1. Henry's law: \(p = K_Hx\). A larger \(K_H\) means lower solubility.
2. Raoult's law: relative lowering of vapour pressure equals the mole fraction of a non-volatile solute.
3. Colligative properties are multiplied by the van't Hoff factor i. For dissociation \(i = 1 + (n-1)\alpha\). For association of n molecules, \(i = 1 - \alpha\left(1 - \dfrac{1}{n}\right)\).
4. Osmotic pressure: \(\pi = iCRT\).

Thermodynamics and Surface Chemistry

1. Extensive properties depend on the amount (volume, mass, energy); intensive properties do not (temperature, density, viscosity).
2. \(\Delta H = \Delta U + \Delta n_g RT\), counting only gaseous species.
3. In free expansion of an ideal gas, \(W = 0\), \(q = 0\) and \(\Delta E = 0\).
4. Physisorption is exothermic and falls as temperature rises. The extent of adsorption increases with pressure.
5. Gold number: milligrams of a protective colloid that prevent coagulation of 10 mL of gold sol by 1 mL of 10% NaCl. Flocculation value is the minimum electrolyte concentration that coagulates a sol.