Chemistry NCERT Exemplar Solutions Class 12th Chapter Six

For expansion in vacuum, workdone, w = 0

For isothermal process,  $\Delta U=0$

According to first law of thermodynamics,

$\begin{array}{l}\Delta U=q+w\\ q=0\end{array}$

Below 1350° C, Mg can reduce Al₂O₃ and above 1350°C, Al can reduce MgO (from Ellingham diagram).

Melting and boiling point of Mg are lower than that of Al.

In ores/mineral available earthy and undesired impurities are gangue

Sol. $Z=101$ belong to actinoids

104 belong to group 4

Sol. $2\mathrm{P}\mathrm{b}{\left({\mathrm{N}\mathrm{O}}_3\right)}_2\stackrel{\mathrm{\Delta }}{?}2\mathrm{P}\mathrm{b}\mathrm{O}+2{\mathrm{N}\mathrm{O}}_2+{\mathrm{O}}_2$

$2{\mathrm{N}\mathrm{O}}_2?{\mathrm{N}}_2{\mathrm{O}}_4$ colourless

${\mathrm{N}}_2{\mathrm{O}}_4+2\mathrm{N}\mathrm{O}?2{\mathrm{N}}_2{\mathrm{O}}_3$

Oxidation state in ${\mathrm{N}}_2{\mathrm{O}}_3$  is +3

Sol. Reactivity towards ${\mathrm{A}\mathrm{g}\mathrm{N}\mathrm{O}}_3$  depend on stability of carbocation formed

Number of moles, n = 5 mol

Temperature, T= 300 K

Initial volume, V₁ = 10L

Final volume, V₂ = 20 L

Using;

Work done; w = -2.303 nRT log₁₀   $\frac{V_2}{V_1}$

$=-2.303*5*8*300lo{g}_{10}\frac{20}{10}J$                

= -8630 J

So, magnitude of work done is 8630 J.

Leaching involves the given reaction,

$4Au\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(aq\right)+O_2\left(g\right)\to 4{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$              

Here, O₂ is required for formation of Au (l) cyanide complex but no complex in absence of O₂.

$2{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+Zn\left(s\right)\to {\left[Zn{\left(CN\right)}_4\right]}^{2-}\left(aq\right)+2Au\left(s\right)$                

In above displacement reaction, Zn is oxidized.

Higher the E.N. difference between hydrogen and other atom then higher be the strength of intermolecular H-bond

Here, order of difference in E.N is

O - H > N – H > C - H

Hence, correct order of H bond strength is,

CH₄ < HCN < NH₃

55.  (ii) Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation: Hydrometallurgy is used to extract copper from low-grade ore. Hydrometallurgy entails dissolving the ore in a suitable reagent and then precipitating it. In this method, more electropositive metal is used, allowing pure metal to be displaced.