Answer the following in one or two sentences.

Question 12 Marks

State Law of Mass action.

Answer

Law of mass action: The law of mass action states that the rate of a chemical reaction at each instant is proportional to the product of concentrations of all the reactants.

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Question 22 Marks

The value of Kc for the dissociation reaction: $H _{2(g)} \rightleftharpoons 2 H _{( g )}$ is $1.2 \times 10^{-42}$ at 500 K . Does the equilibrium mixture contain mainly hydrogen molecules or hydrogen atoms?

Answer

When the value of $K _{ c }$ is very low (that is, $K _{ c }<10^{-3}$ ), then at equilibrium, only a small fraction of the reactants is converted into products.
For the given reaction, $K _{ c } \ll \ll 10^3$ at 500 K .
Hence, the equilibrium mixture contains mainly hydrogen molecules.

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Question 32 Marks

What is a saturated solution?

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Question 42 Marks

Write ideal gas equation with significance of each term involved in it.

Answer

Ideal gas equation is PV = nRT.
where, P = Pressure of the gas
V = Volume of the gas
n = Number of moles of the gas
R = universal gas constant
T = Absolute temperature of the gas

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Question 52 Marks

What are the types of the following changes?
Natural waterfall, spreading of smoke from burning incense stick, diffusion of fragrance of flowers.

Answer

Natural waterfall, spreading of smoke from burning incense stick and diffusion of fragrance of flowers are irreversible physical changes.

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Question 62 Marks

Complete the following table that shows the shifts in the equilibrium position for the reaction:
$N_2O_{4(g)} + Heat ⇌ 2NO_{2(g)}$

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Question 72 Marks

An equilibrium mixture of dinitrogen tetroxide (colourless gas) and nitrogen dioxide (brown gas) is set up in a sealed flask at a particular temperature. Observe the effect of change of pressure on the gaseous equilibrium and complete the following table:

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Question 82 Marks

Write the equilibrium constant expression for the decomposition of baking soda. Deduce the unit of KC from the above expression.

Answer

$2 NaHCO _{3( s )} \rightleftharpoons Na _2 CO _{3( s )}+ CO _{2( g )}+ H _2 O _{( g )}$
$K _{ C }=\frac{\left[ Na _3 CO _{2 (s) }\right)\left( CO _{2(g)}\right)\left(H _2 O _{( g )}\right)}{\left( NaHCO _{3( s)}\right)^2}$
The expression for equilibrium constant does not contain the concentration of pure solids.
$K _{ C }=\left( CO _{2( g )}\right) {\left( H _2 O _{( g )}\right) }$
$\text { Units of } K _{ C } =\left( mol dm ^{-3}\right)\left( mol dm ^{-3}\right)$
$ = mol ^2 dm ^{-6} \text {}$

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Question 92 Marks

Explain in short homogeneous equilibrium and heterogeneous equilibrium.

Answer

i. In a homogeneous equilibrium, the reactants and products are in the same phase.
e.g. Dissociation of $HI$ :
$2 HI _{( g )} \geqslant H _{2( g )}+ I _{2( g )}$
ii. In a heterogeneous equilibrium, the reactants and products exist in different phases, e.g. Formation of $NH _4 Cl$:
$NH _{3( g )}+ HCl _{( g )} \rightleftharpoons NH _4 Cl _{( s )}$

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Question 102 Marks

Write the expressions for $K _{ C }$ and $K _{ p }$ and the relationship between them for the equilibrium reaction,
$2 A _{( g )}+ B _{( g )} \rightleftharpoons 3 C _{( g )}+2 D _{( g )}$

Answer

$\begin{array}{lc}2 A _{( g )}+ B _{( g )} \rightleftharpoons 3 C _{( g )}+2 D _{( g )} \\ K _{ P }=\frac{\left( P _{ C }\right)^3 \times\left( P _{ D }\right)^2}{\left( P _{ A }\right)^2 \times\left( P _{ B }\right)} & K _{ C }=\frac{[ C ]^3[ D ]^2}{[ A ]^2[ B ]} \\ K _{ P }= K _{ C }( RT )^{\Delta n } & \text { } \\ K _{ P }= K _{ C }( RT )^2 & {[\because \Delta n =(3+2)-(2+1)=2]}\end{array}$

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Question 112 Marks

For a chemical equilibrium reaction
$H _{2( g )}+ I _{2( g )} \rightleftharpoons 2 HI _{( g )}$
write an expression for $K _{ p }$ (and relate it to $K _{ C }$ ).

Answer

For the given reaction, $K _{ P }=\frac{\left( P _{ HI }\right)^2}{\left( P _{ H _2}\right)\left( P _{ t _2}\right)}$

$\begin{array}{ll}\therefore & K _{ P }=\frac{\left[ HI _{(g)}\right]^2[ RT ]^2}{\left[ H _{2(g)}\right] RT \cdot\left[1_{2(9)}\right]RT } \\\therefore & K _{ P }=\frac{\left[ HI _{(g)}\right]^2}{\left[ H _{2(g)}\right]\left[1_{2(g)}\right]} \times \frac{[ RT ]^2}{[ RT ][ RT ]} \\\therefore & K _{ P }= K _{ C } \times( RT )^{2-(1+1)} \\\therefore & K _{ p }= K _{ C } \quad \text {}\end{array}$

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Question 122 Marks

$N _{2( g )}+3 H _{2( g )} \rightleftharpoons 2 NH _{3( g )}$
Write expressions for $Kp _{}$ and substitute expressions for $P _{ N _{2^{\prime}}}, P _{ H _2}$ and $P _{ NH _3}$ using ideal gas equation.

Answer

$\begin{array}{ll}\text { For the given reaction, } K _{ p }=\frac{\left(P_{ NH _3}\right)^2}{\left(P_{ N _2}\right)\left(P_{ H _2}\right)^3} \\ \therefore K _{ P }=\frac{\left[ NH _{3( g)}\right]^2[ RT ]^2}{\left[ N _{2(g)}\right] RT \left[ H _{2(g)}\right]^3[ RT ]^3} \\ \therefore K _{ P }=\frac{\left[ NH _{3(g) }\right]^2}{\left[ N _{2(g) }\right]\left[ H _{2(g)}\right]^3} \times \frac{[ RT ]^2}{[ RT ][ RT ]^3} \\ \therefore K _{ p }= K _{ C } \times( RT )^{2-(3+1)} \\ \therefore K _{ p }= K _{ C } \times( RT )^{-2} \text { }\end{array}$

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Question 132 Marks

How are the equilibrium constants of the following pair of equilibrium reactions related?
i. $\quad CO _{2(g)}+ N _{2(g)} \stackrel{ K _C}{\rightleftharpoons} CO _{( g )}+ N _2 O _{( g )}$
ii. $\quad CO _{( g )}+ N _2 O _{( g )} \stackrel{ K _{ C }^{\prime}}{\rightleftharpoons} CO _{2( g )}+ N _{2( g )}$

Answer

i. $\quad K _{ C }=\frac{[ CO ]\left[ N _2 O \right]}{\left[ CO _2\right]\left[ N _2\right]}$
From (i) and (ii), $\quad K _{ C }=\frac{1}{ K _{ C }^{\prime}}$
ii. $K _{ C }=\frac{\left[ CO _2\right]\left[ N _2\right]}{[ CO ]\left[ N _2 O \right]}$

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Question 142 Marks

Write equilibrium constant expressions for both forward and reverse reaction for the synthesis of ammonia by the Haber process.

Answer

Synthesis of ammonia by Haber process:
$ N _{2( g )}+3 H _{2( g )} \rightleftharpoons 2 NH _{3( g )} $
Forward reaction: $K _{ C }=\frac{\left[ NH _3\right]^2}{\left[ N _2\right]\left[ H _2\right]^3}$
Reverse reaction: $K _{ C }^{\prime}=\frac{\left[ N _2\right]\left[ H _2\right]^3}{\left[ NH _3\right]^2 \text { }}$

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Question 152 Marks

Write the rate equation for the following reactions:
i. $C + O _2 \rightarrow CO _2$
ii. $2 KClO _3 \rightarrow 2 KCl +3 O _2$

Answer

The rate equation is written by applying the law of mass action.
i. The reactants are $C$ and $O _2$
Rate $\propto[ C ]\left[ O _2\right]$
$\therefore$ Rate $= k [ C ]\left[ O _2\right]$

ii. The reactant is $KClO _3$ and its 2 molecules appear in the balanced equation.
$\therefore$ Rate $\propto\left[ KClO _3\right]^2$
$\therefore$ Rate $= k \left[ KClO _3\right]^2$

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Question 162 Marks

Identify the type of equilibrium in the following physical processes:
$i.$ Camphor$_{(s)}$ ⇌ Camphor$_{(g)}$
$ii.$ Ammonium chloride$_{(s)}$ ⇌ Ammonium chloride$_{(g)}$
$iii.$ Carbon dioxide gas ⇌ Dry ice
$iv.$ Water ⇌ Ice

Answer

$i.$ Solid $–$ vapour equilibrium
$ii.$ Solid $–$ vapour equilibrium Solid
$iii.$ Solid $–$ vapour equilibrium
$iv.$ Solid $–$ liquid equilibrium

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Question 172 Marks

What is meant by the term ‘normal boiling point’ of a liquid?

Answer

For any pure liquid at 1 atm pressure, the temperature at which its saturated vapour pressure equals to atmospheric pressure is called the normal boiling point of that liquid.
e.g. The boiling point of ethyl alcohol is 78 °C i.e., the saturated vapour pressure of ethyl alcohol at 78 °C is 1 atm (1.013 bar).

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Chemistry Answer the following in one or two sentences.

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