States of Matter

For combustion of Mg:

Mg (s) + $\frac{1}{2}{O}_2\left(g\right)\to MgO\left(s\right)$

Here,   $\Delta ng=-\frac{1}{2}$

Now using

$\Delta H=\Delta U+\Delta ngRT$

-601.7 =   $\Delta U+\left(-\frac{1}{2}\right)*8.3*10^{-3}*300$

$\Delta U=-600.45kJ$

So; magnitude of   $\Delta U$ is 600 kJ (the nearest integer).

Moles of N₂O $\frac{2.2}{44}=\frac{1}{20}$

$\Delta H=n{C}_p\Delta T=\frac{1}{20}*100\left(-40\right)=-200J$

$\Delta U=q_p+w$

$w=-P_{ext}.\Delta V$

$w=-1\frac{\left(167.75-217.1\right)}{1000}*101.3J=+5J$

$\Delta U=-200+5=195J$

Here, total meq of acetic acid = 50 * 0.1 = 5

And total meq of NaOH = 25 * 0.1 = 2.5

After neutralization process

Meq of left acetic acid = 2.5

And meq of formed CH₃COONa = 2.5

$pH=pKa+lo{g}_{10}\frac{\left[S\right]}{\left[A\right]}$

$pH=4.76+lo{g}_{10}\frac{2.5}{2.5}=4.76=476*10^{-2}$

5.41. Ideal Gas: A gas that follows Boyle's law, Charles' law and Avogadro law strictly, is called an ideal gas. It is assumed that intermolecular forces are not present between the molecules of an ideal gas.

Real Gases: Gases which deviate from ideal gas behaviour are known as real gases. NH₃ is expected to show more deviation. Since NH₃ is polar in nature and it can be liquified easily.

5.40. (a) Surface tension: It is defined as the force acting per unit length perpendicular to the line drawn on the surface.

(b) Surface tension of a liquid depends upon following factors.

(i) Temperature: Surface tension decreases with rise in temperature. As the temperature of the liquid increases the average kinetic energy of the molecules increases. Thus, there is a decrease in intermolecular force of attraction which decreases the surface tension.

(ii) Nature of the liquid: Greater the magnitude of intermolecular forces of attraction in the liquid, greater will be the value of surface tension.

5.39. In liquids, the molecules are more compact in comparison to gases.

5.38. The temperature at which a real gas obeys ideal gas law over an appreciable range of pressure, is called Boyle temperature or Boyle point.

5.37.  (i) Surface tension decreases with increase of temperature.

(ii) Viscosity decreases with increase of temperature.