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Gibbs energy change and equilibrium - class-XI

Description: gibbs energy change and equilibrium
Number of Questions: 47
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Tags: thermodynamics energetics and thermochemistry chemical thermodynamics chemistry
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At equilibrium, the value of equilibrium constant $K$ is:

  1. $1$

  2. $2$

  3. $3$

  4. $0$


Correct Option: A
Explanation:

At equilibrium $\Delta G=0$
$\Delta G=-nRT ln K$
$0=-nRT ln K$
or $K=1$

The equilibrium constants of a reaction is $73$. Calculate standard free energy change.

  1. $-106\ kJ\ mol^{-1}$

  2. $0.632\ kJ\ mol^{-1}$

  3. $60.32\ kJ\ mol^{-1}$

  4. $-10.632\ kJ\ mol^{-1}$


Correct Option: D
Explanation:

${ \triangle G }^{ 0 }=-RTlnK$             $T={ 27 }^{ 0 }C=300K$

${ \triangle G }^{ 0 }=-8.3\times 300\times ln73$
          $=-10.632KJ{ mol }^{ -1 }$

The Van't Hoff equation is :

  1. $\Delta G^{\circ} = RT log _e K _p$

  2. $-\Delta G^{\circ} = RT log _e K _p$

  3. $\Delta G^{\circ} = RT^2 lnK _p$

  4. None of the above


Correct Option: B
Explanation:

The Van't Hoff equation gives the relationship between the standard gibbs free energy change and the equilibrium constant.  It is represented by the equation $-\Delta  G^{\circ} = RT    log _e   K _p$.

Standard Gibbs Free energy change $\Delta { G }^{ o }$ for a reaction is zero. The value of equilibrium constant of the reaction will be:

  1. 0

  2. 1

  3. 2

  4. 3


Correct Option: B
Explanation:

$\text{Option B is correct.}$


$\Delta{G^o}=-RTlog K _c$
$0=-nRTlogK _c$
$logK _c=0$
$K _c=1$

if for the heterogeneous equilibrium $CaCO _{3}(s)\rightleftharpoons CaO(s)+CO _{2}(g);$ K=1 at 1 atm, the temperature is given by:

  1. $T=\frac{\Delta S^{0}}{\Delta H^{0}}$

  2. $T=\frac{\Delta H^{0}}{\Delta S^{0}}$

  3. $T=\frac{\Delta G^{0}}{ R^{0}}$

  4. $T=\frac{\Delta G^{0}}{\Delta H^{0}}$


Correct Option: B
Explanation:

$\Delta G = 2.303RT\space logK$


As K =1 , $\Delta G = 0$

We know the relation,

$\Delta G = \Delta H - T\Delta S$

$T = \dfrac{\Delta H}{\Delta S}$

Option B is correct

A reaction attains equilibrium, when the free energy change is

  1. $1$

  2. $2$

  3. $3$

  4. $0$


Correct Option: D
Explanation:

As we know,
At equilibrium $\Delta G=0$

Vant Hoff's equation is ___.

  1.  ${log\frac{K _2}{K _1}=\frac{-\Delta H^{0}}{2.303R}\left [ \frac{T _2-T _1}{T _2T _1} \right ]}$.

  2.  ${log\frac{K _2}{K _1}=\frac{\Delta H^{0}}{2.303R}\left [ \frac{T _2-T _1}{T _2+T _1} \right ]}$.

  3.  ${log\frac{K _2}{K _1}=\frac{\Delta H^{0}}{2.303R}\left [ \frac{T _2-T _1}{T _2T _1} \right ]}$.

  4.  ${log\frac{K _2}{K _1}=\frac{\Delta H^{0}}{2.303R}\left [ \frac{T _2+T _1}{T _2T _1} \right ]}$.


Correct Option: C
Explanation:
The van't Hoff equation provides information about the temperature dependence of the equilibrium constant. The van't Hoff equation may be derived from the Gibbs-Helmholtz equation, which gives the temperature dependence of the Gibbs free energy.

The van't Hoff equation is $K=Ae^{\Delta H/RT}$ or $\displaystyle\frac {d ln K}{\partial T}=\frac {\Delta H}{RT^2}$

By, integrating the above equation, you will get the required relation.

Hence, the given statement is correct

Calculate the standard voltage that can be obtained from an ethane oxygen fuel cell at $25^o C$.
$C _2H _6(g) + 7/2O _2(g) \rightarrow 2CO _2(g) + 3H _2O(1); \Delta G^o = -1467 \,kJ$

  1. $+0.91$

  2. $+0.54$

  3. $+0.72$

  4. $+1.08$


Correct Option: C

Expansion of a perfect gas into vacuum is related with:

  1. $\Delta H=0$

  2. $q=0$

  3. $W=0$

  4. All the above


Correct Option: D
Explanation:
Solution -
If an ideal gas or perfect gas 
expands into vacuum, it does 
no work 
i.e, work done = 0 

& this process is considered to 
be an adiabatic process, 
where $ q = 0 $
$ \Delta U = 0 $

Also, $\Delta H = \Delta U+Work \,done $
$ \Delta H = 0+0 $
$ \Delta H = 0 $

Hence, the answer is all of these.

Which are correct representation at equilibrium?

  1. $\displaystyle p=\frac { eRT }{ N } $

  2. $\displaystyle K={ e }^{ { { -\Delta G }^{ o } }/{ RT } }$

  3. $\displaystyle \frac { { K } _{ 1 } }{ { K } _{ 2 } } ={ e }^{ { { -E } _{ a } }/{ RT } }$

  4. $\displaystyle \frac { P }{ { P }^{ o } } ={ e }^{ { -\Delta H }/{ RT } }$


Correct Option: A,B,C,D

Although dissolution of $NH _{4}Cl$ in water is endothermic yet it dissolves because:

  1. $\Delta $ G is positive

  2. $\Delta $ H is positive

  3. $\Delta $ S is positive

  4. $\Delta $ A is positive


Correct Option: B

The correct relationship between free energy change in a reaction and the corresponding equilibrium constant $\displaystyle { K } _{ c }$ is:

  1. $\displaystyle { \Delta G }^{ o }=RTIn{ K } _{ c }$

  2. $\displaystyle -{ \Delta G }^{ o }=RTIn{ K } _{ c }$

  3. $\displaystyle { \Delta G }=RTIn{ K } _{ c }$

  4. $\displaystyle -{ \Delta G }=RTIn{ K } _{ c }$


Correct Option: B
Explanation:

$\displaystyle \because \quad \Delta G={ \Delta G }^{ o }+RTInQ$, where Q is reaction quotient at equilibrium, $\displaystyle \Delta G=0$ and $\displaystyle Q={ K } _{ c }$
$\displaystyle \therefore \quad -\Delta G=RTIn{ K } _{ c }$

For the reaction : $\displaystyle 2NOCl(g)\longrightarrow 2NO(g)+{ Cl } _{ 2 }(g)$, The equilibrium constant at 400K, if $\displaystyle { \Delta H }^{ o }=77.18kJ{ mol }^{ -1 }$ and $\displaystyle { \Delta S }^{ o }=0.122kJ{ K }^{ -1 }{ mol }^{ -1 }$ is:

  1. $\displaystyle 1.97\times { 10 }^{ -3 }$

  2. $\displaystyle 1.97\times { 10 }^{ -2 }$

  3. $\displaystyle 1.97\times { 10 }^{ -4 }$

  4. $\displaystyle 1.97\times { 10 }^{ -1 }$


Correct Option: C
Explanation:
Given the reaction: $2NOCl(g)\rightarrow 2NO(g)+Cl _2(g)$

$\Delta G^o=\Delta H^o-T\Delta S^o$

$\Delta G^o=77.18-400\times 0.122kJmol^{-1}$

$\Delta G^o=28.38\ kJmol^{-1}$

$K=e^{(\dfrac{-\Delta G^o}{RT})} $

$=1.97\times 10^{-4}$

Hence, option C is correct.

van't Hoff equation is

  1. $(d/dT) ln K=-\Delta H/RT^2$

  2. $(d/dT) ln K=+\Delta H/RT^2$

  3. $(d/dT) ln K=-\Delta H/RT$

  4. $K=Ae^{\Delta H/RT}$


Correct Option: B,D
Explanation:

The van't Hoff equation provides information about the temperature dependence of the equilibrium constant. The van't Hoff equation may be derived from the Gibbs-Helmholtz equation, which gives the temperature dependence of the Gibbs free energy.
The van't Hoff equation is $K=Ae^{\Delta H/RT}$
or $\frac {d ln K}{\partial T}=\frac {\Delta H}{RT^2}$

The rate of disappearance of A at two temperatures is given by $A\rightleftharpoons B$
i. $\frac {-d[A]}{dt}=2\times 10^{-2}[A]-4\times 10^{-3}[B]$ at 300 K
ii. $\frac {-d[A]}{dt}=4\times 10^{-2}[A]-16\times 10^{-4}[B]$ at 300 K
From the given values of heat of reaction which are incorrect

  1. $3.86 kcal$

  2. $6.93 kcal$

  3. $1.68 kcal$

  4. $1.68\times 10^{-2} kcal$


Correct Option: B,C,D
Explanation:

$K _1=\frac {K _f}{K _b}=\frac {2\times 10^{-2}}{4\times 10^{-3}}=5$ at 300 K
$K _2=\frac {K _f}{K _b}=\frac {4\times 10^{-2}}{16\times 10^{-4}}=25$ at 400 K
$\therefore 2.303 log\frac {25}{55}=\frac {\Delta H}{2}\times \left [\frac {400-300}{400\times 300}\right ]$
or $\Delta H=3.85 kcal$

Hence, option A is correct and others are incorrect

${ K } _{ C }$ for ${ 3 }/{ 2{ H } _{ 2 }+{ 1 }/{ 2{ N } _{ 2 }\rightleftharpoons  } }{ NH } _{ 3 }$ are 0.0266 and $0.0129\,{ atm }^{ -1 }\quad $ respectively, at 350$^o$C and 400$^o$C. Calculate the heat of formation of ${ NH } _{ 3 }$.

  1. $\therefore \triangle H =\,-50462\quad cal$

  2. $\therefore \triangle H=\,-8133\quad cal$

  3. $\therefore \triangle H =\,12140\quad cal$

  4. $\therefore \triangle H=\,-12140\quad cal$


Correct Option: D
Explanation:

As we know,
$2.303\,log[\displaystyle\frac { { K } _{ { P } _{ 2 } } }{ { K } _{ { P
} _{ 1 } } }] =\frac { \triangle H }{ R } \left[ \frac { { T } _{ 2 }-{ T
} _{ 1 } }{ { T } _{ 1 }{ T } _{ 2 } }  \right] $
$2.303\,log[\displaystyle\frac
{ 0.0129 }{ 0.0266 }] =\frac { \triangle H }{ 2 } \left[ \frac {
673-623 }{ 673\times 623 }  \right] $
$\therefore \triangle H=\,12140\quad cal\quad =\,-12140\quad cal$

For the equilibrium at $298$ K; $N _2O _4(g)\rightleftharpoons 2NO _2(g); G _{N _2O _4}^{\ominus}=100 kJ mol^{-1}$ and $G _{NO _2}^{\ominus}=50 kJ mol^{-1}$. If 5 mol of $N _2O _4$ and 2 moles of $NO _2$ are taken initially in one litre container than which statement are correct

  1. reaction proceeds in forward direction

  2. $K _c=1$

  3. $\Delta G=-0.55 kJ, \Delta G^{\ominus}=0$

  4. At equilibrium $[N _2O _4]=4.84 M$ and $[NO _2]=0.212 M$


Correct Option: A,B,C
Explanation:

$\Delta G=\Delta G^{\ominus}+2.303 RT:log Q$

$\Delta G^{\ominus}=2\times G _{NO _2}^{\ominus}-G _{N _2O _4}^{\ominus}=2\times 50-100=0$

$\therefore \Delta G=0+2.303\times 8.314\times 10^{-3}\times 298: log \displaystyle\frac {22}{5}=0-0.55 kJ$

$\therefore \Delta G=-0.55 kJ$, i.e, reaction proceeds in forward direction

Also $\Delta G^{\ominus}=0=2.303 RT:log K \therefore K=1$

Now, $\underset {\underset {5-x}{5}}{N _2O _4}=\underset {\underset {2+2x}{2}}{2NO _2}$

$\therefore K _p=\frac {(P _{NO _2})}{(P _{N _2O _4})}=1=\frac {(2+2x)^2}{5-x}$ or  $x=0.106$


So, $[N _2O _4]=5-x=4.894M,\ [NO _2]=2+2x=2.12M$

Hence, options A, B and C are correct.

The equilibrium constant is $10$ at $100 K$. Hence, $\Delta G$ will be negative.
  1. True

  2. False


Correct Option: A
Explanation:

The equilibrium constant is 10 at 100 K. Hence, $\Delta G$ will be negative.
$\Delta G = -RTlnK = -RTln10 = -RT \times 2.303$ Since R and T are positive, $\Delta G$ is negative.

Which are true for the reaction: $A _2\rightleftharpoons 2C+D$?

  1. If $\Delta H=0; K _p$ increases with temperature and dissociation temperature.

  2. If $\Delta H=+ve; K _p$ increases with temperature and dissociation of $A _2$ increases.

  3. If $\Delta H=-ve; K _p$ increases with temperature and dissociation of $A _2$ decreases.

  4. $K _p=4\alpha^3\left [\frac {P}{1+2\alpha}\right ]^2$


Correct Option: A,B,C,D
Explanation:

Initial At equilibrium
$\underset {\underset {1-\alpha}{1}}{A _2}\rightleftharpoons \underset {\underset {2\alpha}{0}}{2C}+\underset {\underset {\alpha}{0}}{D}$
$K _p=(2\alpha)^2\alpha \times \left [\frac {P}{\Delta n}\right ]^2=\frac {4\alpha^3P^2}{(1+2\alpha)^2}$
Also, as we know
2.303 log $\frac {K _2}{K _1}=\frac {\Delta H}{R}\left [\frac {T _2-T _1}{T _1T _2}\right ]$ for effect temperature on K.
If $\Delta H=+ve; K _p$ increases with temperature and dissociation of $A _2$ increases.
If $\Delta H=-ve; K _p$ decreases with temperature and dissociation of $A _2$ decreases.

Concrete is produced from a mixture of cement, water and small stones. Small amount of gypsum, $CaSO _4\cdot 2H _2O$ is added in cement production to improve the subsequent hardening of concrete. 
The elevated temperature during the production of cement may lead to the formation of unwanted hemihydrate $CaSO _4\cdot \frac { 1 }{ 2 }H _2O$ according to reaction.

$CaSO _4\cdot 2H _2O(s)\rightarrow CaSO _4\cdot \frac { 1 }{ 2 }H _2O(s) + \frac { 3 }{ 2 }H _2O(g)$
The $\Delta _f H^{ \ominus }$ of $CaSO _4\cdot 2H _2O(s),\ CaSO _4\frac { 1 }{ 2 }H _2O(s),\ H _2O(g)$ are $-2021.0  kJ  mol^{ -1 }$, $-1575.0  kJ  mol^{ -1 }$ and $-241.8  kJ  mol^{ -1 }$ respectively. The respective values of their standard entropies are $194.0$, $130.0$ and $188.0  J  K^{ -1 }  mol^{ -1 }.$ 
$R = 8.314  J  K^{ -1 }  mol^{ -1 } = 0.0831  L  bar  mol^{ -1 }  K^{-1}$
Answer the follwoing questions on the basis of above information.
The value of equilibrium constant for reaction is:

  1. 0

  2. <1

  3. >1

  4. =1


Correct Option: B
Explanation:

$\Delta H^{ \ominus } = \Delta H^{ \ominus } _ { P } - \Delta H^{ \ominus } _{ R }; (for\quad 1\quad mol)$
$= \left[ -1575.0 kJ mol^{ -1 }-\frac { 3 }{ 2 } \times 241.8 \right] -\left[ -2021.0 kJ mol^{ -1 } \right] $
$= +83.3 kJ mol^{ -1 }$
For 1 Kg $CaSO _4\cdot 2H _2O$
Numebr of moles $=\frac { 1000}{ 172 }$
$= 5.81$
$\therefore$ Heat change for $5.81\quad mol\quad of\quad CaSO _4\cdot 2H _2O = 5.81\times 83.3 kJ mol^{ -1 }$
$=484 kJ mol^{ -1 }$
$\Delta G = \Delta H - T\Delta S$
$= 17.92 kJ$ ........ $(\Delta S = S _P - S _R)$
$\Delta G = -nRTln K$
$\therefore$ $K = e^{ -\Delta GlnRT } < 1$

${\Delta G ^{0}}$ is related to K by the relation _____.

  1.  ${\Delta G ^{0}}$ =$ -RT: InK^{2}$.

  2.  ${\Delta G ^{0}}$ =$ -RTK$.

  3.  ${\Delta G ^{0}}$ =$ RT: InK$.

  4.  ${\Delta G ^{0}}$ =$ -RT: InK$.


Correct Option: D
Explanation:
$G=G^o+RTlnK$.

$G^o$ is standard Gibbs energy. At equillibrium when there is no longer free energy left to drive the reaction then $\Delta G=0, \Delta G^o=-RTlnK$ 

The correct relationship between free energy change in a reaction and the corresponding equilibrium constant $K$ is 

  1. $-\Delta G=RT:\ln:K$

  2. $\Delta G^{o}=RT:\ln:K$

  3. $\Delta G=-RT:\ln:K$

  4. $-\Delta G^{o}=RT:\ln:K$


Correct Option: C
Explanation:

The correct relationship between free energy change in a reaction and the corresponding equilibrium constant K is $-\Delta G=RT:ln:K$ or $\Delta G=-RT:ln:K$

$\Delta G = \Delta G^{ \ominus } + RT log K$
  1. True

  2. False


Correct Option: A
Explanation:

As we know,
$\Delta G = \Delta H - T\Delta S$
Also, 
$\Delta G = \Delta G^{ \ominus } + RT log K$
and at equilibrium,
$\Delta G = 0$ so
$\Delta G^{ \ominus } = - RT log K$

For the reaction at $298 K$


$A (g) + B (g)\rightleftharpoons C (g) + D (g)$

$\Delta H^o = 29.8 kcal ; \Delta S^o = 0.1 kcal/K$

Calculate $\Delta G^o$ and $K$.

  1. $\Delta G^o = 0 ; K = 1$

  2. $\Delta G^o = 1 ; K = e$

  3. $\Delta G^o = 2 ; K = e^2$

  4. None of these


Correct Option: A
Explanation:

As we know,


$\Delta G^o = \Delta H^o - T\Delta S^o$ 

         $= 29.8 - ( 298\times0.1 )$

         $= 29.8-29.8=0$

Therefore, $\Delta G^o = 0$

The relation between $\Delta G^0 $ and $K$

$\Delta G^0$ = $ - RT lnK$

$K = 1 $

So, the correct option is $A$

When $\displaystyle \Delta G$ is zero :

  1. reaction moves in forward direction

  2. reaction moves in backward direction

  3. system is at equilibrium

  4. none of these


Correct Option: C
Explanation:

When $\displaystyle \Delta G$ is zero, system is at equilibrium.
Positive free energy change corresponds to non spontaneous reaction.
Negative free energy change corresponds to spontaneous reaction.

The density of an equilibrium mixture of $N _2O _4$ and $NO _2$ at 101.32 $KP _a$ is 3.62 g $dm^{3}$ at 288 K and 1.84 g $dm^{3}$ at 348 K. 


What is the heat of the reaction for the following reaction?

$N _2O _4\rightleftharpoons 2NO _2(g)$

  1. $\Delta _rH = 37.29 $  kJ mol$^{ -1 }$. 

  2. $\Delta _rH = 75.68 $  kJ mol$^{ -1 }$. 

  3. $\Delta _rH = 95.7$  kJ mol$^{ -1 }$. 

  4. $\Delta _rH = 151.3 $  kJ mol$^{ -1 }$. 


Correct Option: B
Explanation:

At 288 K, $M _{avg.}=\frac {3.62\times 0.0821\times 288}{1}$
$\frac {92}{M _{avg.}}=1+\alpha \Rightarrow K _{P1}=\frac {4\alpha^2}{1-\alpha^2}$
Similarly at $348 K, M'/avg.=\frac {1.84\times 0.0821\times 348}{1}$
$\frac {92}{M'avg}=1+\alpha'\Rightarrow K _{P _2}=\frac {4\alpha'^2}{1-\alpha'^2}$
$log \frac {K _{P _2}}{K _{P _1}}=\frac {\Delta H^o}{2.303 R}\left [\frac {1}{288}-\frac {1}{348}\right ]$
so,
$\Delta _rH = 75.68 kJ mol^{1}$

Which is not correct relationship between $\Delta G^{ \ominus }$ and equilibrium constant $K _P$

  1. $K _P = -RT log \Delta G^{ \ominus }$

  2. $K _P = [e/RT]^{ \Delta G^{ \ominus } }$

  3. $K _P = -\frac { \Delta G^{ \ominus } }{ RT }$

  4. $K _P = e^{ -\Delta G^{ \ominus }/RT }$


Correct Option: A,B,C
Explanation:

$\Delta G = \Delta G^{ \ominus } + RT log K$
and at equilibrium,
$\Delta G = 0$ so
$\Delta G^{ \ominus } = - RT log K$
$\Delta G^{ \ominus } = -RTln K _P$
$K _P = e^{ -\Delta G^{ \ominus }/RT }$

The correct relation between equilibrium constant $(K)$, standard free  energy $(\Delta {G}^{o})$ and temperature $(T)$ is:

  1. $\Delta {G}^{o}=RT\ln {K}$

  2. $K={ e }^{ \Delta { G }^{ o }/2.303 RT }\quad $

  3. $\Delta { G }^{ o }=-RT\log{K}$

  4. $K={ 10 }^{ -\Delta { G }^{ o }/2.303 RT }\quad $


Correct Option: D
Explanation:

Consider a reaction, $A+B\rightleftharpoons C+D$

$\Delta G={ \Delta G }^{ 0 }+RTlnQ$
for equilibrium, $\Delta G=0$
$\therefore \quad 0={ \Delta G }^{ 0 }+RTlnK$
$\therefore \quad { \Delta G }^{ 0 }=-RTlnK$
$\therefore \quad { \Delta G }^{ 0 }=-2.303RTlogK$
i.e. $K={ 10 }^{ { -\Delta G }^{ 0 }/2.303RT }$

When $\ln{K}$ is plotted against $\cfrac { 1 }{ T } $ using the Van't Hoff equation, a straight line is expected with a slope equal to:

  1. $\Delta { H }^{ o }/RT$

  2. $-\Delta { H }^{ o }/R$

  3. $\Delta { H }^{ o }/R$

  4. $R/\Delta { H }^{ o }$


Correct Option: B

If we know $\displaystyle { \Delta G }^{ \circ  }$ of a reaction, which of the following can be defined ?
I. Cell potential, $\displaystyle { E }^{ \circ  }$
II. Activation energy, $\displaystyle { E } _{ a }$
III. Equilibrium constant, $\displaystyle { K } _{ eq }$

  1. I and II only

  2. I and III only

  3. III only

  4. I, II, III

  5. None of these


Correct Option: B
Explanation:

If we know $\displaystyle \Delta G^o $  of a reaction, the following can be defined. 
I. Cell potential, $\displaystyle E^o $
III. Equilibrium constant, Keq
$\displaystyle \Delta G^o = -nF E^o = - RTlnK $

For the first order reaction $A\longrightarrow B+C$, carried out at $27^0C  $ if  $ 3.8\ \times \ 10^{ -16 } \%$ of the reactant molecules exists in the activated state, the ${ E } _{ a }$ (activation energy) of the reaction is:

  1. 12 kJ/mole

  2. 831.4 kJ/mole

  3. 100 kJ/mole

  4. 88.57 kJ/mole


Correct Option: A

By which of the following relations, the equilibrium constant varies with temperature?

  1. $\ln { { K } _{ 2 } } -\ln { { K } _{ 1 } } =\cfrac { \Delta { H }^{ o } }{ R } \int _{ { T } _{ 1 } }^{ { T } _{ 2 } }{ d\left( \cfrac { 1 }{ T } \right) } $

  2. $\ln { { K } _{ 2 } } -\ln { { K } _{ 1 } } =-\cfrac { \Delta { H }^{ o } }{ R } \int _{ { 1/T } _{ 1 } }^{ { 1/T } _{ 2 } }{ d\left( \cfrac { 1 }{ { T }^{ 2 } } \right) } $

  3. $\ln { { K } _{ 2 } } -\ln { { K } _{ 1 } } =-\cfrac { \Delta { H }^{ o } }{ R } \int _{ { T } _{ 1 } }^{ { T } _{ 2 } }{ d\left( \cfrac { 1 }{ T } \right) } $

  4. $\ln { { K } _{ 2 } } -\ln { { K } _{ 1 } } =-\cfrac { \Delta { H }^{ o } }{ R } \int _{ { 1/T } _{ 2 } }^{ { 1/T } _{ 1 } }{ d\left( \cfrac { 1 }{ { T }^{ } } \right) } $


Correct Option: C
Explanation:
$\textbf{Explanation:}$

  • We can use $\mathit{Gibbs-Helmholtz}$ to get the temperature dependence of $K$                                                                                            
$\mathbf{\left ( \frac{\partial \left [ \Delta _{r}G^{o} \right ]}{\partial T} \right )}$   $\mathbf{=\frac{-\Delta _{r}H^{o}}{T^{2}}}$     $\mathbf{\rightarrow \left ( 1 \right )}$

  • At equilibrium, we can equate $\Delta _{r}G^{o}$ to $-RTlnK$ so we get

  $\mathbf{\left ( \frac{\partial \left [ lnK \right ]}{\partial T} \right )= \frac{\Delta _{r}H^{o}}{RT^{2}}}$    $\mathbf{\rightarrow (2)}$

  • We see that whether  K  increases or decreases with temperature is linked to whether the reaction enthalpy is positive or negative. If the temperature is changed little enough that  $\Delta _rH^{o}$  can be considered constant, we can translate a  $K$  value at one temperature into another by integrating the above expression, we get a similar derivation as with melting point depression:

$\mathbf{ln\frac{K\left ( T _{2} \right )}{K\left ( T _{1} \right )}=\frac{-\Delta _{r}H^{o}}{R}\left ( \frac{1}{T _{2}}-\frac{1}{T _{1}} \right )}$$\mathbf{\rightarrow \left ( 3 \right )}$

  • If we integrate and differentiate the left side of the equation then we get and solve the right side we get

$\mathbf{lnK _{2}-lnK _{1}=\frac{-\Delta H^{0}}{R}\int _{T _{1}}^{T _{2}}\mathbf{\mathit{d}}\left ( \frac{1}{T} \right )}$$\mathbf{\rightarrow (4)}$

Hence from equation $4$ we can say that option $C$ is correct.

Calculate the Standard Free Energy Change at 25 degrees celsius given the Equilibrium constant of 1.3 x 10^4.

  1. +23.4 kJ

    • 3.22 x 10^4 kJ
  2. -23,400 kJ

  3. -23.4 kJ

  4. +23,400 kJ


Correct Option: D
Explanation:

 The temperature is 25 deg C or 298 K.
$\displaystyle  \Delta G^o = -RT ln K = - 8.314 \times 298 \times ln 1.3 \times 10^4 = -23469 J = -23.4 kJ$
Hence, the standard free energy change is -23.4 kJ

The cell in which the following reaction occurs:
$2Fe^{3+} _{(aq)}+2I^- _{(aq)}\rightarrow 2Fe^{2+} _{(aq)}+I _{2(s)}$ has $E^o _{cell}=0.236\ V$ at $298\ K$.
The equilibrium constant of the cell reaction is:

  1. $6.69\times 10^{-7}$

  2. $7.69\times 10^{-7}$

  3. $9.69\times 10^7$

  4. $6.69\times 10^7$


Correct Option: C
Explanation:
We know
$\log K _c=\dfrac{nFE^0 _{cell}}{2.303RT}$
where,
$n=2$
$F=96487$
$E^0 _{cell}=0.236\ V$
$R=8.31$
$T=298$
Substituting the values, we get
$\log K _c=\dfrac{2\times96487\times0.236}{2.303\times8.31\times298}$
$\log K _c=7.9854$
$K _c=antilog (7.9854)$
$K _c=9.69\times10^7$

In dynamic equilibrium condition, the reaction on both the sides occurs at the same rate and the mass on both sides of the equilibrium does not undergo any change. This condition can be achieved only when the value of $\Delta$G is :

  1. -1

  2. +1

  3. +2

  4. 0


Correct Option: D
Explanation:
The Gibb's free energy change ($\Delta G$) is:
$\Delta G<0 \longrightarrow$ Spontaneous process
$\Delta G>0 \longrightarrow$  Non-spontaneous process
$\Delta G=0 \longrightarrow$ Equilibrium process
Therefore, the condition of dynamic equilibrium can be achieved only when $\Delta G=0$.

The equilibrium constant of a reaction is 10. What will be the value of $\Delta G^0$ at 300 K?

    • 5.74 kJ
    • 574 kJ
    • 11.48 kJ
  1. +5.74 kJ


Correct Option: A
Explanation:

$\Delta G $= -2.303 RT log K
 = $-2.303 \times 8.314 \times 300 \ log 10$
=-5.74 kJ

A reaction attains equilibrium state under standard conditions. Identify the incorrect option regarding this statement.

  1. Equilibrium constant K = 0

  2. Equilibrium constant K = 1

  3. $\Delta G^0$ = 0 and $\Delta H^0$ = T$\Delta S^0$

  4. All options are correct


Correct Option: A
Explanation:

$\Delta G^0 = 0 $ at equilibrium under standard state.
Also at equilibrium, $\Delta G  = 0 $
$\therefore$ $\Delta H^0 - T\Delta S^0 = 0$
Also $\Delta G^0 $= -2.303 RT Iog K  
$\therefore$ K = 1

For a spontaneous reaction the $\Delta G$, equilibrium constant $(K _{eq})$ and $E^{0} _{cell}$ will be respectively 

  1. -ve , >1 , -ve

  2. -ve , <1 , -ve

  3. +ve , >1 , -ve

  4. -ve , >1 , +ve


Correct Option: D
Explanation:

$\Delta G^{o}=- R TlnKeq$

$\Delta G^{o}=$ will be negative for spontaneous process

$Keqm > 1$for spontaneous process 

$E^{o} cell > O$ for spontaneous process

$nFE _{cell}^{o}= RT ln Keq$

$\therefore E _{cell}^{o}>o$

For a reversible reaction, if $\Delta { G }^{ o }=0$, the equilibrium constant of the reaction should be equal to:

  1. Zero

  2. $1$

  3. $2$

  4. $10$


Correct Option: B
Explanation:
If $\Delta {G}^{o}=0$

At equilibrium $\Delta G=0$

$\Delta G=\Delta {G}^{o}+RT\ln {K} _{eq}$

$0=0+RT\ln {K} _{eq}$

$\ln {K} _{eq}=0$

${K} _{eq}=1$

equilibrium constant $=1$

Option B is correct.

$\Delta G^o (298 K)$ for the reaction $\dfrac12 N _2+\dfrac32H _2\overset {K _1}{\rightleftharpoons} NH _3$ is -16.5 kJ $mol^{-1}$. The equilibrium constant $(K _1)$ at $25^oC$ & the equilibrium constant $K _2$ and $K _3$ for the following reactions are
$N _2+3H _2\overset {K _2}{\rightleftharpoons} 2NH _3$
$NH _3\overset {K _3}{\rightleftharpoons } \dfrac12N _2+\dfrac32H _2$

  1. $K _1 = 779.4, K _2 = 6.074 \times 10^{5} ; K _3 = 1.283 \times 10^{-3}$

  2. $K _1 = 779.4, K _2 = 2.183 \times 10^{5} ; K _3 = 3.576 \times 10^{3}$

  3. $K _1 = 124.4, K _2 = 6.074 \times 10^{5} ; K _3 = 2.34\times 10^{3}$

  4. $None ::of ::these $


Correct Option: A
Explanation:


 $\displaystyle \Delta G^o = -RTlnK _1$
 $\displaystyle -16500 = - 8.314 \times 298 \times lnK _1$
$\displaystyle 6.6597 = ln K _1$
 $\displaystyle K _1 = 779.4$
$\displaystyle K _2 = K _1^2 = (779.4)^2 = 6.074 \times 10^5$
 $\displaystyle K _3 = \dfrac {1}{K _1}=\dfrac {1}{779.4}=1.283 \times 10^{-3} $

Calculate the equilibrium constant at 25 degrees celsius given the Standard Free Energy value of - 107.2 kJ

    • 43.2
  1. 43.2

  2. 6.18 x $ 10^8$

  3. 1.04

  4. 6.18 x $10^9$


Correct Option: C
Explanation:

 The temperature is 25 deg C or 298 K
$\displaystyle  \Delta G^0 = -RT lnK$
$\displaystyle  \Delta G^0 = - 107.2 kJ = -107200 J$
$\displaystyle  -107200 = - 8.314 \times 298 \times ln K$
$\displaystyle  ln K = 43.268$
$\displaystyle  K = 6.18 \times 10^{18}$

A large positive value of $\Delta { G }^{ o }$ corresponds to which of these?

  1. Small positive $K$

  2. Small negative $K$

  3. Large positive $K$

  4. Large negative $K$


Correct Option: A
Explanation:

A large positive value of $\Delta { G }^{ o }$ corresponds to small positive $K$.
$\Delta { G }^{ o }=-2.303RT\log { { K } _{ c } } $
When $ \displaystyle  { K } _{ c }  >0$, $ \displaystyle \Delta { G }^{ o } <0 $ and vice versa.

If $\Delta G$ standard is zero, this means :

  1. the reaction is both spontaneous and at equilibrium

  2. the system is at equilibrium at standard conditions

  3. the reaction is non spontaneous at standard conditions

  4. the reaction is spontaneous at standard conditions

  5. the reaction is both non spontaneous and at equilibrium


Correct Option: B
Explanation:

If $\Delta G = 0$ this means, the system is at equilibrium at standard conditions.
$\Delta G = 0$, it means the reaction is equilibrium at standard conditions.
A negative value of $\Delta G  $, means spontaneous.
A positive value of $\Delta G $, means non-spontaneous.

If ${E} _{cell}^{o}$ for a given reaction is negative, which gives the correct relationships for the values of $\Delta { G }^{ o }$ and ${K} _{eq.}$?

  1. $\Delta { G }^{ o }>0,{ K } _{ eq. }<1$

  2. $\Delta { G }^{ o }>0,{ K } _{ eq. }>1$

  3. $\Delta { G }^{ o }<0,{ K } _{ eq. }>1$

  4. $\Delta { G }^{ o }<0,{ K } _{ eq. }<1$


Correct Option: A
Explanation:
$\mathbf{Explanation:}$

From the relation between change in free energy$(\Delta G)$ and equilibrium constant $(K _{eq})$ we have :

$\mathbf{\Delta G=-RTlnK _{eq}}$      $\mathbf{\rightarrow (1)}$

where:
$\Delta G=$ The change in free energy
$R=$ Gas constant
$T=$ The absolute temperature
$K _{eq}=$ Equilibrium constant
 
From the relation between change in energy $\Delta G$ and $E _{cell}(E^{o})$ we have :

$\mathbf{\Delta G=-nFE^{o}}$ $\mathbf{\rightarrow (2)}$

$\Delta G=$ The change in free energy
$E^{o}=E _{cell}$
$n =$ moles of e- from balanced redox reaction
$F =$ Faraday's constant 

From equation  $(2) $ if $E^{o}< 0$ then $\Delta G>0$$\mathbf{\rightarrow (3)}$

If then $lnK<1$ and then $K _{eq}<1$ that is positive $\mathbf{\rightarrow (4)}$ 

From $(3)$ and $(4)$ we get that

$\mathbf{\Delta G>0}$ and $\mathbf{K _{eq}}<1$

Hence the correct answer is option $A$.

Consider the reaction of extraction of gold from its ore
$Au + 2CN^{-} (aq.) + \dfrac {1}{4}O _{2}(g) + \dfrac {1}{2}H _{2}O\rightarrow Au(CN) _{2}^{-} + OH^{-}$
Use the following data to calculate $\triangle G^{\circ}$ for the reaction
$K _{f} \left {Au(CN) _{2}^{-}\right ) = X$
$O _{2} + 2H _{2}O + 4e^{-}\rightarrow 4OH^{-}; E^{\circ} = +0.41\ volt$
$Au^{3+} + 3e^{-}\rightarrow Au; E^{\circ} = + 1.5\ volt$
$Au^{3+} + 2e^{-} \rightarrow Au^{+}; E^{\circ} = + 1.4\ volt$.

  1. $-RT\ ln\ X + 1.29\ F$

  2. $-RT\ ln\ X - 2.11\ F$

  3. $-RT\ ln \dfrac {1}{X} + 2.11\ f$

  4. $-RT\ ln\ X - 1.29\ F$


Correct Option: A

The value of $log _{10}$ K for a reaction $A\rightleftharpoons B$ is:

$( Given : \Delta _{r}H^{0} _{298k}=-54.07 kJ mol^{-1},$ $\Delta _{r}S^{0} _{298k}=10JK^{-1}mol^{-1}$ $and\ R=8.314 JK^{-1}mol^{-1};$ 
$2.303\times 8.314\times 298=5705 )$

  1. 5

  2. 10

  3. 95

  4. 100


Correct Option: B
Explanation:

$\Delta G^{0}=\Delta H^{0}-T\Delta S^{0}=-54.07 \times 1000 - 298 \times 10$

$=-54070-2980=-57050$

$\Delta G^{0}=-2.303 RT log _{10}K$

$-57050=-2.303\times 298\times 8.314 log _{10}K=-5705 log _{10}K$


$ log _{10}K=10$

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