Chemistry · Physics

Thermodynamics and Chemical Kinetics

1,092 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 reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Which of the following statements is correct?

  1. The rate of a reaction decreases with passage of time as the concentration of reactants decreases.

  2. The rate of a reaction is same at any time during the reaction.

  3. The rate of a reaction is independent of temperature change.

  4. The rate of a reaction decreases with increase in concentration of reaction(s).
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to rate law expression,
$Rate \propto [R]$
Thus, rate of a reaction decreases with passage of time as the concentration of reactants decreases.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Statement 1: The temperature of a substance always increases as heat energy is added to the system.
Statement 2: The average kinetic energy of the particles in the system increases with an increase in temperature.

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

  2. Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1.

  3. Statement 1 is correct but Statement 2 is not correct.

  4. Statement 1 is not correct but Statement 2 is correct.

  5. Both the Statement 1 and Statement 2 are not correct.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Energy can neither be created nor be destroyed. It is only converted in one form or the other. Addition of heat energy increases the kinetic energy which is dependent on absolute temperature.

$\therefore $ Temperature also increases when heat energy is added.
Hence, Statement 1 and statement 2 are correct and statement 2 is the correct explanation of statement 1.

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

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

  1. $-\Delta G^{\circ}\, =\, RT\, in \, K$
  2. $\Delta G\, =\, RT\, in\, K$
  3. $-\, \Delta G \, =\, RT\, in\, K$
  4. $\Delta G^{\circ}\, =\, RT\, in\, K$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The equilibrium constant is related to the free energy change of the reaction by the expression:

$K = e^{(-\Delta G^o/RT)}$ or $ln K = - \Delta G^o/RT$

or  $- \Delta G^o= RT \ ln K$ in which $T$ is the temperature in Kelvin and $R$ is the gas constant (1.986 cal/K mol)

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

Assertion: For every chemical reaction at equilibrium, the standard Gibbs energy of reaction is zero.
Reason: At constant temperature and pressure, chemical reactions are spontaneous in the direction of decreasing Gibbs energy.

  1. The Assertion is True, Reason is True; Reason is the correct explanation for Assertion

  2. The Assertion is True, Reason is True; Reason is NOT a correct explanation for Assertion

  3. The Assertion is True, Reason is False

  4. The Assertion is False, Reason is True
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation


The standard Gibb's energy for a reaction is given by $\Delta G^o$.

At equilibrium, $\Delta \mathrm{G}=0$ whereas $\ \Delta \mathrm{G}^{\mathrm{o}}$ for a reaction may or may not be zero.
For a spontaneous process, Gibb's energy for a reaction is always negative, $\Delta \mathrm{G}<0$
Hence, Assertion is false but Reason is true.

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

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

  1. $\Delta G^{o} = -RT ln K$
  2. $\Delta G = RT ln K$
  3. $\Delta G = -RT ln K$
  4. $\Delta G^{o} = RT ln K$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Here, $R$ is the ideal gas constant and $T$ is the temperature.

Multiple choice chemistry chemical equilibrium relationship between equilibrium constant, reaction quotient and gibbs energy law of mass action chemical equilibrium and acids-bases
Greenhouse gas $CO _2$ can be converted to $CO(g)$ by the following reaction

$CO _2(g)+H _2(g)\rightarrow CO(g)+H _2O(g)$,
 
termed as water gas reaction.

$\Delta G$ for the reaction at 1000 K is : 

 $(\Delta H _{\displaystyle1000\;K}=35040\;J\;mol^{-1}\ ; \Delta S _{1000\;K}=32.11\;J\;mol^{-1}\ K^{-1})$

  1. $2930\;J$
  2. $2934\;J$
  3. $2300\;J$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A.2930J
$\triangle G=\triangle H-T\triangle S\ \triangle G=35040-1000\times 32.11\ \quad \quad \quad \quad =35040-32110\ \quad \quad \quad \quad =2930J$

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

A reaction mixture containing $H _2,\, N _2$ and $NH _3$ has partial pressure 2 atm, 1atm and 3 atm respectively at 725 K. If the value of K for the reaction. $N _2\, +\, 3H _2\, \rightleftharpoons\,  2NH _3$ is $4.28\, \times\, 10^{-5}$ 

atm$^{- 2}$ at 725 K, in which direction the net reaction will go:

  1. forward

  2. backward

  3. no net reaction

  4. direction of reaction cannot be predicted
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$Q _p =\dfrac{p^2 _{NH _3}}{p _{N _2}p^3 _{H _2}}$ $=\dfrac{3^2}{1 \times 2^3}=1.125 \ atm^{-1}$

Since it is grater that $K _p$ the reaction will go in backward direction to achieve $K _P$

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

When reaction is at standard state at equilibrium, then:

  1. $\Delta H^\circ\, =\, 0$
  2. $\Delta S^\circ\, =\, 0$
  3. equilibrium constant $K = 0$
  4. equilibrium constant $K = 1$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If $K$ is equal to 1, the reaction will reach equilibrium as an intermediate mixture, meaning the amounts of products and reactants will be about the same.

Multiple choice chemistry chemical thermodynamics calorific value occurrence of carbon compounds in nature study of enthalpy

Gross and net calorific value of fuel will be the same :

  1. if its ash content is zero

  2. under no circumstances

  3. if its carbon content is very low

  4. if its hydrogen/hydrogen compound content is zero
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The gross or high heating value is the amount of heat produced by the complete combustion of a unit quantity of fuel. 


The net, or lower, value is determined by calculation and equals the gross calorific value minus the latent heat of the water vapor formed from the combustion of hydrogen and from any moisture present in the fuel. 

Gross and net calorific value of a fuel will be the same if its hydrogen compound content is zero.

Hence, option $D$ is correct.

Multiple choice chemistry occurrence of carbon compounds in nature calorific value study of enthalpy chemical thermodynamics

Gross & net calorific value is the same for ___________.

  1. blast furnace gas

  2. coke oven gas

  3. L.D. converter gas

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gross & net calorific value is the same for L.D converter gas. Calorific value is the total quantity of heat liberated by the complete combustion of a unit mass of the fuel in air or oxygen. It is expressed in $kcal/m^3$ or British thermal unit (B.T.U) per cubic foot.