Bond energy : It may be defined as the energy released when two atoms get bonded or it is equal to the energy required to break the bond to form the neutral atoms .

e.g , H-H (g) $\to$ H + H , $∆$H = + 103 Kcal/mol

Heat of neutralisation for strong acid and strong base is always close to 13.7 kcal .

$\underset{\mathrm{strong} \mathrm{acid}}{\mathrm{HA}}$ + $\underset{\mathrm{strong} \mathrm{base}}{\mathrm{BOH}}$ $\rightleftharpoons$ H₂O + AB

$∆$H = - 13.7 Kcal

The heat of neutralisation of strong acid and strong base is actually the heat of formation of 1 gmole of water from 1 g of H⁺ and 1 g of OH^- .

Orbital angular momentum = $\sqrt{\mathrm{l} (\mathrm{l} + 1 )}$ $\frac{\mathrm{h}}{2\mathrm{\pi }}$

where l = azimuthal quantum number

$\frac{\sqrt{6}\mathrm{h}}{2\mathrm{\pi }}$

Heisenberg's uncertainty principle :  It is not possible to determine precisely both the position and the momentum (or velocity) of a small moving particle (e.g , electron , proton etc)

$∆$x . $∆$p $⩾$ $\frac{\mathrm{h}}{4\mathrm{\pi }}$

where $∆$x , $∆$p are the uncertainties with regard to position , momentum respectively .

Methane (CH₃) shows the sp³ hybridisation .So , the geometry of methane molecule is tetrahedral .

0.02 M HCl = 2 x 10^-2 M HCl

[H⁺] = 2 x 10^-2

pH = - log[H⁺]

= - log [2 x 10^-2]

= - log 2 + 2 log 10

= - 0.3010 + 2

= 1.7

Mg(OH)₂ $\rightleftharpoons$ Mg²⁺ + 2OH^-

K_sp = [Mg²⁺][OH^-]²

1.4 X 10^-11 = (s)(2s)²

1.4 X 10^-11 = 4s³

s = 1.5 x 10^-4 mol/L

($\because$Mol. wt. of Mg(OH)₂ = 52)

= 58 X 1.5 x 10^-4

= 0.0087 g/L

Hess's law is based upon conservation of energy .

$\because$ Heat evolved during the formation of 44 g of CO₂ = - 93kJ

$\therefore$ Heat evolved in the formation of 0.156 kg of CO₂

=$\frac{- 393 \times 156}{44}$

= - 1393 kJ

E = mc²

E = hv

mc² = hv

$\mathrm{\nu }$ = $\frac{{\mathrm{mc}}^2}{\mathrm{h}}$ = $\frac{1.1 \times {10}^{-23} \times 3 \times {10}^8}{6.6 \times {10}^{-34}}$

= 5  x 10¹⁸ Hz