Tag: introduction to equilibrium

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Multiple choice chemistry chemical equilibrium equilibrium in physical processes introduction to equilibrium 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?
$H _2O _{(l)} \rightarrow H _2O _{(g)}$

  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 $K^{-1}mol^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 } $
                     $=\dfrac { 40.98\times 1000 }{ 373 } =109.8{ JK }^{ -1 }{ mol }^{ -1 }$

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

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

  1. 282.4 K

  2. 373.6 K

  3. 100 K

  4. 400 K
Reveal answer Fill a bubble to check yourself
B Correct answer
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) $

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

Which of the following represent physical equlibrium?

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Physical equilibrium involves a physical process where the rate of the forward process equals the rate of the reverse process. Dissolution of a solid in a saturated solution is a classic example of physical equilibrium.

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

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:

  1. $Tin$
  2. $Antimony$
  3. $Arsenic$
  4. $Cadmium$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In qualitative analysis, Tin (Sn) sulfides (SnS2) are soluble in yellow ammonium sulfide or NaOH, forming a soluble complex, and precipitate upon acidification with dil. HNO3 or HCl.

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

Which of the following statements is incorrect ?

  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 .
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Adding oxalic acid to a solution containing iron(III) nitrate and potassium thiocyanate forms stable Fe-oxalate complexes, which consumes free Fe3+ ions. According to Le Chatelier's principle, this shifts the equilibrium for the formation of the red iron-thiocyanate complex backward, causing the red color to fade, not increase. Thus, statement B is incorrect.

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

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 __________.

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

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

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

  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 .
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Equilibrium is a dynamic process, not a static one. Even at equilibrium, the forward and backward processes continue to occur at the same rate; they do not stop.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

Gaseous $ N _{2}O _{4} $ dissociates into gaseous $ NO _{2} $ according to the reaction $ N _{2}O _{4} (g) \rightleftharpoons 2NO _{2}(g)$ at 300 K and 1 atm pressure, the degree of dissociation of $ N _{2}O _{4} $ is 0.2. If one mole of $ N _{2}O _{4} $ gas is contained in a vessel, then the density of the equilibrium mixture is : 

  1. 3.11 g/L

  2. 4.56 g/L

  3. 1.56 g/L

  4. 6.22 g/L
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$N _2O _4\longrightarrow 2NO _2$


at $t=0$, moles of $N _2O _4=1$, moles of $NO _2=0$

at $t=equilibrium$, mole of $N _2O _4=1-a$, mole of $NO _2=2a$

$a$=degree of dissociation.

Molecular weight of mixture$=\cfrac {(1-a)\times\text{molar mass of }N _2O _4+2a\times \text{molar mass of }NO _2}{(1-a+2a)}$
                                                $=\cfrac {(1-0.2)(28+64)+2\times 0.2\times (14+32)}{1+0.2}$
$M=76.66$

$P=1 atm,T=300K,$

$d=PM/RT$

    $=\cfrac {1\times 76.66}{0.082 \times 300}=3.11\  gm/lit\ $ .

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

Attainment of equilibrium in a coloured gaseous reversible reaction is detected by the constancy of:

  1. colour

  2. density

  3. pressure

  4. all the above properties of the mixture
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The intensity of color represents the concentration of either reactant or product. Thus when in a colored gaseous reversible reaction, the color has attained constant intensity, the concentrations of reactants and products have reached equilibrium values. In other words, an equilibrium is attained.


Hence, the correct option is A.