Tag: chemical equilibrium and acids-bases

Questions Related to chemical equilibrium and acids-bases

At 373 K, steam and water are in equilibrium and $\Delta H$ = 40.98 kJ $mol^{-1}$.What will be  $\Delta S$ fro conversion of water into steam?
$H _2O _{(l)} \rightarrow H _2O _{(g)}$

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. 109.8 J $K^{-1}mol^{-1}$

  2. 31 J $K^{-1}mol^{-1}$

  3. 21.98 J $K^{-1}mol^{-1}$

  4. 326 J $K^{-1}mol^{-1}$

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Correct Option: A
Explanation:

The given reaction is :-

${ H } _{ 2 }O\left( l \right) \longrightarrow { H } _{ 2 }O\left( g \right) $
So, we have
       $\triangle Svap=\dfrac { \triangle Hvap }{ Tb } $
                     $=\dfrac { 40.98\times 1000 }{ 373 } =109.8{ JK }^{ -1 }{ mol }^{ -1 }$

At what temperature liquid water will be in equilibrium with water vapour?
$\Delta H _{vap} = 40.73 \ kJ \ mol^{-1}$, $\Delta S _{vap} = 0.109 \ kJ \ K^{-1} \ mol^{-1}$, 

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. 282.4 K

  2. 373.6 K

  3. 100 K

  4. 400 K

Show answer
Correct Option: B
Explanation:

The given reaction is :-

               ${ H } _{ 2 }O\left( l \right) \rightleftharpoons { H } _{ 2 }O\left( g \right) $
Now, at equilibrium, $\triangle G=0$
Now, from fibb's free energy change equation
         $\triangle G=\triangle H-T\triangle S$
$\Rightarrow \quad \triangle H=T\triangle S$
$\Rightarrow \quad T=\dfrac { \triangle H }{ \triangle S } =\dfrac { 40.73 }{ 0.1079 } =373.6K$
$\left( \because \triangle Hrap=40.73KJ/mol,\quad \triangle Srap=0.109KJ{ K }^{ -1 }{ mol }^{ -1 } \right) $

In physical equilibrium, forces responsible for equilibrium are _______ in  nature.

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. physical

  2. chemical

  3. strong

  4. weak

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Correct Option: A
Explanation:

In physical equilibrium, forces responsible for equilibrium are physical in nature (factual).

Which of the following represent physical equlibrium?

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. Dissolution of solid $KI$ in water

  2. Sublimation of $NH _4Cl$

  3. Evaporation of dry ice in a closed container

  4. Condesation of water vapours

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Correct Option: A

A yellow precipitate obatined in II group of the equilibrium analysis was soluble in aq. $NaOH$ and insoluble in dil. $HNO _3$. This shows the presence of:

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. $Tin$

  2. $Antimony$

  3. $Arsenic$

  4. $Cadmium$

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Correct Option: A

Which of the following statements is incorrect ?

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. In equilibrium mixture of ice water kept in perfectly insulated flask mass of ice and water does not change with time .

  2. The intensity of red colour increase when oxalic acid is added to a solution containing iron (III) nitrate and potassium thioyanate .

  3. On addition of catalyst equilibrium constant value is not affected .

  4. Equilibrium constant for a reaction with negative $\triangle H$ value decreases as the temperature increases .

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Correct Option: A

Two flasks A and B of an equal volume containing 1 mole and 2 moles of O$ 3$ respectively are heated to the same temperature. When the reaction $2O _3 \rightleftharpoons 3O _2$ practically stops, then both the flasks shall have __________.

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. the same ratio: $[O _2]/[O _3]$

  2. the same ratio: $[O _2]^{3/2}/[O _3]$

  3. only $O _2$

  4. the same time to reach equilibrium

Show answer
Correct Option: B
Explanation:

For the given reaction,
$K _c = \displaystyle \frac{[O _2]^3}{[O _3]^2}= constant$     so  $\displaystyle \sqrt{K _c} = \frac{[O _2]^{3/2}}{[O _3]} = constant$
Same for both containers. Kc won't change as flasks are heated to same temperature. 

Which of the following is not a general characteristic of equilibrium involving physical processes ?

chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium chemical equilibrium and acids-bases

  1. equilibrium is possible only in a closed system at a given temperature .

  2. all measurable properties of the system remain constant .

  3. all the physical processes stop at equilibrium.

  4. the opposing processes occur at the same ratio and there is dynamic but stable condition .

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Correct Option: C

The equilibrium constant $K p$ for the reaction $2H _2(g) + O _2(g)  \rightleftharpoons 2H _2O(g)$ at 2000 K is $1.6 \times 10^7$. The equilibrium constant of the reaction $H _2O(g)  \rightleftharpoons H _2(g) + \frac{1}{2} O _2(g)$ is _______.

chemistry chemical equilibrium relationship between equilibrium constant, reaction quotient and gibbs energy law of mass action chemical equilibrium and acids-bases

  1. $6.25 \times 10^{-8}$

  2. $2.5 \times 10^{-4}$

  3. $7.5 \times 10^{-12}$

  4. $4\times 10^{-6}$

Show answer
Correct Option: B
Explanation:

For the reaction, $2H _2(g) + O _2(g)  \rightleftharpoons 2H _2O(g)$,
$K = \dfrac{{[H _2O]}^{2} _{}} {{[H _2]}^{2} _{} [{O} _{2}]}$

$2H _2O(g)  \rightleftharpoons 2H _2(g) + O _2(g)$
$K = \dfrac{{[H _2]}^{2} _{} [{O} _{2}]}{[{H _2O}]^{2} _{}}$

$H _2O(g)  \rightleftharpoons H _2(g) + \frac{1}{2} O _2(g)$
$K _1 = \sqrt{\dfrac{{[H _2O]}^{2} _{}} {{[H _2]}^{2} _{} [{O} _{2}]}}$

Thus, $K _1 = \dfrac{1}{\sqrt{1.6107}}$$= 2.5 \times 10^{-4}$

Which of the following is true about the reaction quotient?

chemistry chemical equilibrium relationship between equilibrium constant, reaction quotient and gibbs energy law of mass action chemical equilibrium and acids-bases

  1. It relates the ratio of the concentrations of products to reactants once the reaction has reached chemical equilibrium.

  2. It is always equal to the equilibrium constant.

  3. It can never be equal to the equilibrium constant.

  4. It relates the concentrations of products to reactants at any point in time.

  5. None of these answers are correct

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Correct Option: D
Explanation:

The reaction quotient relates the concentrations of products to reactants at any point in time.
When equilibrium is attained, the reaction quotient is equal to the equilibrium constant.