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 energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

The efficiency of a fuel cell is given by:

  1. $\frac{\Delta S}{\Delta G}$
  2. $\frac{\Delta H}{\Delta G}$
  3. $\frac{\Delta G}{\Delta S}$
  4. $\frac{\Delta G}{\Delta H}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The fuel cell thermodynamic efficiency is given by the ratio of the Gibbs function change to the Enthalpy change in the overall cell reaction. The Gibbs function change measures the electrical work and the enthalpy change is a measure of the heating value of the fuel. 
Efficiency = $ \frac{dG}{dH} $$=\frac{\Delta G}{\Delta H}$
Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

What is the approximate value of $ \Delta S^{\circ} $ for the fuel cell reaction at $ 25^{\circ}$? 

  1. $ -0.1624\,JK^{-1}$
  2. $ -162.4\,JK^{-1} $
  3. $ +162.4\,JK^{-1} $
  4. $ +0.1624\,JK^{-1} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The question asks for the standard entropy change of a fuel cell reaction at 25°C but does not specify the reaction. Without knowing the specific fuel cell reaction (e.g., H2/O2, methanol, etc.), the value cannot be verified. The magnitude -162.4 JK^-1 is plausible for a multi-electron process like hydrogen oxidation but requires reaction context.

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Which of the following statements regarding fuel cell is (are) true?

  1. They have efficiency of about 60-70%

  2. There efficiency is less then conventional methods

  3. They do not cause pollution

  4. They can supply indefinite amount of energy until outside supply of reactants is maintained
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

Fuel cells have efficiency of 60-70%. Reactants, products and catalyst used are non- toxic, thus, they are pollution-free. And they can supply indefinite amount of energy until outside supply of reactants like H$ _{2}$ and O$ _{2}$  is maintained.

Multiple choice physics energy and its forms introduction to work work introduction to work and energy

State the wrong statement 

  1. Total work done by internal force in a system is always zero

  2. Work done is different as seen from different frames of reference

  3. In the absence of external forces and non-conservation force , the molecules energy of a system remains conserved

  4. a non conservation force always do negative work
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Non-conservative forces (like friction) can do positive work (e.g., if a force acts in the direction of displacement). Thus, the statement that they always do negative work is false.

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

When a chemical reaction takes place, during the course of the reaction the rate of reaction?

  1. Keeps on increasing with time

  2. Remains constant with time

  3. Keeps on decreasing with time

  4. Shows irregular trend with time
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of reaction $\propto$ conc. of reactants
As the reaction proceeds, concentration of the reactants decreases hence the rate also keeps on decreasing with time.

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

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 $K _P$