Chemistry · Physics

Thermodynamics and Chemical Kinetics

1,132 Questions

Thermodynamics and chemical kinetics are crucial branches of physical chemistry. This area focuses on energy transformations, reaction rates, equilibrium constants, and catalysts. These topics carry significant weight in competitive science and engineering examinations.

Enthalpy and energyChemical equilibriumEntropy conceptsReaction kinetics and catalysts

Thermodynamics and Chemical Kinetics Questions

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

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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
Reveal answer Fill a bubble to check yourself
D Correct answer
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

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

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

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

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. $10$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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 $K$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. <font><font class="">the reaction is both spontaneous and at equilibrium</font></font>

  2. <font><font>the system is at equilibrium at standard conditions</font></font>

  3. <font><font class="">the reaction is non spontaneous at standard conditions</font></font>

  4. <font><font>the reaction is spontaneous at standard conditions</font></font>

  5. <font><font>the reaction is both non spontaneous and at equilibrium</font></font>
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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. $\Delta { G }^{ o }<0,{ K } _{ eq. }<1$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $A$.
Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

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

Multiple choice physics measurement and effects of heat heat exchange calorimeter measuring thermal quantities by the method of mixtures

On which law does the study of calorimetry based?

  1. Joule's law

  2. Law of conservation of energy

  3. Law of Kinetic energy

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Principle of calorimetry states that heat lost by a hotter body = heat gained by a colder body, therefore in calorimetry, total heat energy of the system remains constant, which is the law of conservation of energy . 

Multiple choice

Relationship between temperature and kinetic energy of particles in a substance

  1. As kinetic energy increases, temperature increases

  2. As kinetic energy decreases, temperature increases

  3. As kinetic energy increases, temperature decreases

  4. As kinetic energy decreases, temperature decreases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Temperature is a measure of the average kinetic energy of the particles in a substance. As particles move faster, their kinetic energy increases, which corresponds to a higher temperature.

Multiple choice

Adding Thermal Energy to a Substance does not cause

  1. change the state - liquid to solid or gas to liquid

  2. increase in the kinetic energy of the particles

  3. vibration of individual particles will increase

  4. change the state - solid to liquid or liquid to gas
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Adding thermal energy increases kinetic energy and particle vibration, causing transitions like solid to liquid or liquid to gas. Option A describes removing energy, which causes cooling and condensation or freezing.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

The internal energy of a gas:

  1. is the sum total of kinetic and potential energies.

  2. is the total transitional kinetic energies

  3. is the total kinetic energy of randomly moving molecules.

  4. is the total kinetic energy of gas molecules
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

At a given temperature, the pressure of a container is determined by the number of times gas molecules strike the container walls. If the gas is compressed to a smaller volume, then the same number of molecules will strike against a smaller surface area; the number of collisions against the container will increase, and, by extension, the pressure will increase as well.
Increasing the kinetic energy of the particles will increase the pressure of the gas.
So, the internal energy of a gas Is the total kinetic energy of randomly moving molecules.
Hence, option C is correct.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

On increasing temperature of the reacting system by $10$ degrees the rate of reaction almost doubles. The most appropriate reason for this is

  1. collision frequency increases

  2. activation energy decreases by increases in temperatuer

  3. the fraction of molecules having energy equal to threshold energy or more increase

  4. the value of threshold energy decreases
Reveal answer Fill a bubble to check yourself
A Correct answer