Tag: gibbs free energy

Questions Related to gibbs free energy

At equilibrium, the value of equilibrium constant $K$ is:

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  1. $1$

  2. $2$

  3. $3$

  4. $0$

Show answer
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.

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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

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

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

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

Show answer
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 :

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  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

Show answer
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:

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  1. 0

  2. 1

  3. 2

  4. 3

Show answer
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:

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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

Show answer
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

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  1. $1$

  2. $2$

  3. $3$

  4. $0$

Show answer
Correct Option: D
Explanation:

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

Vant Hoff's equation is ___.

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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

Show answer
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 $25^o C$.
$C _2H _6(g) + 7/2O _2(g) \rightarrow 2CO _2(g) + 3H _2O(1); \Delta G^o = -1467 \,kJ$

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  1. $+0.91$

  2. $+0.54$

  3. $+0.72$

  4. $+1.08$

Show answer
Correct Option: C

Expansion of a perfect gas into vacuum is related with:

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

  1. $\Delta H=0$

  2. $q=0$

  3. $W=0$

  4. All the above

Show answer
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?

chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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

Show answer
Correct Option: A,B,C,D