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 biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

An enzyme increases the rate of a reaction by?

  1. enzymes speed up reactions by lowering activation energy.

  2. Increasing the rate of random collisions of molecules

  3. Removing the product of the reaction so allowing it to continue

  4. Bringing the reacting molecules into precise orientation with each other
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation


  • Enzymes provide activation energy for the reactions they catalyze.
  • Catalysts lower the activation energy for reactions. 
  • The lower the activation energy for a reaction, the faster the rate. Thus enzymes speed up reactions by lowering activation energy.so, option A is correct.

Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Chemical reactions require energy for

  1. Oxidation

  2. Entropy

  3. Activation

  4. Enthalpy
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Chemical reactions take place mainly at a specific temperature in presence of a catalyst. The substrate and product have different energy state. The energy gap between the substrate and the product is known as activation energy which is the minimum energy required to initiate a reaction. In presence of a catalyst, the activation energy lowers and the substrate changes into the product.

So, the correct answer is option C.

Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Energy required for start of a chemical reaction is

  1. Activation energy

  2. Entropy

  3. Potential energy

  4. Kinetic energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Entropy is a measure of thermal energy.
Potential energy is the energy stored in an object at a particular height.
Kinetic energy is the energy stored in an object in motion.
Enzymes are proteins which accelerate the rate of the reaction. The substrate and product have different energy state. The energy gap between the substrate and the product is known as activation energy which is the minimum energy required to initiate a reaction. The enzymes lower the activation energy and lead to the faster conversion of substrate to the product.
So, the correct answer is option A.
Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Activation energy is required for :

  1. Bringing reactants together

  2. Destabilisation of bonds of reactants.

  3. Both A and B

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Activation energy is the energy required to bring reactants into a transition state, which involves both bringing them together in the correct orientation and destabilizing their existing bonds to facilitate the reaction.

Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

Enzymes enhance rate of reaction by

  1. Combining with product

  2. Forming reactant-product complex

  3. Changing equilibrium of reaction

  4. Lowering activation energy
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Enzymes are proteins which accelerate the rate of the reaction. The substrate and product have different energy state. The energy gap between the substrate and the product is known as activation energy which is the minimum energy required to initiate a reaction. The enzymes lower the activation energy and lead to the faster conversion of substrate to the product.

So, the correct answer is option D.

Multiple choice biology metabolism, cell respiration, and photosynthesis metabolism enzymes carbohydrate metabolism

An enzyme promotes a chemical reaction by

  1. lowering the energy of activation

  2. changing the free energy difference between substrate and product

  3. increasing molecular motion

  4. all of these.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
There are so many reactions occurring inside the living body that the activation energy of all these reactions cannot be supplied. So, enzymes decrease the activation energy of the reaction and thus increase the speed of the reaction.
So, the correct option is 'lowering the energy of activation'
Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases
When the equilibrium is attained, the concentration of each of the reactants and products becomes equal.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the equilibrium is attained, the concentration of each of the reactants and products may or may not become equal.  It may happen that the concentrations of products are higher than the concentrations of the reactants. Or, it may happen that the concentrations of the reactants are higher than the concentrations of the products.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

Which is the following are true about the chemical equilibrium?

  1. The chemical equilibrium is a state in which the rate of the forward reaction is equal to the rate of the reverse reaction.

  2. The chemical equilibrium takes at least 10 hours to be established.

  3. The chemical equilibrium is a state in which the rate of the forward reaction is not equal to the rate of the reverse reaction.

  4. The chemical equilibrium can only occur at temperatures above room temperature.

  5. None of these answers are correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The following is true about the chemical equilibrium.
The chemical equilibrium is a state in which the rate of the forward reaction is equal to the rate of the reverse reaction. A chemical equilibrium is a state of balance in a reaction where the forward and reverse reaction speed is equal and the concentrations of the products and reactants remain unchanged.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

Identify the common property for a chemical reaction at dynamic equilibrium.

  1. The measurable properties like concentration, density, colour, pressure etc remain constant at constant temperature

  2. The forward and backward reactions take place with the same rate

  3. It can be achieved from both directions

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At dynamic equilibrium, the reaction rate of the forward reaction is equal to the reaction rate of the backward reaction. A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state. Equilibrium is the state of equal, opposite rates, not equal concentrations. The measurable properties like concentration, density, color, pressure etc remain constant at constant temperature.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

When equilibrium is attained, the concentration of each of the reactants and products become equal.

  1. True

  2. False

  3. Ambiguous

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

Equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time.Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s).

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

In reversible reactions concentration of:

  1. reactants decreases with time at equilibrium

  2. products increases with time at equilibrium

  3. reactants decreases and then increases with time at equilibrium

  4. reactants and products are constant at equilibrium
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In reversible reactions, as equation the rates of forward and backward reactions are same so the concentrations of reactants and products are constant at equilibrium.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

Which of the following factors are equal in a reversible chemical reaction at equilibrium?

  1. The number of moles of the reactants and products

  2. The potential energies of the reactants and products

  3. The activation energies of the forward and reverse reactions

  4. The rates of reaction for the forward and reverse reactions

  5. The concentrations of the reactants and products.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The rates of reaction for the forward and reverse reactions are equal in a reversible chemical reaction at equilibrium. When the concentrations of reactants and products have become constant, a reaction is said to have reached a point of equilibrium. The consistency of measurable properties such as concentration, color, pressure and density can show a state of equilibrium. The rates of the two opposing reactions have become equal. The amount of products and reactants produced are consistent, and there is no net change.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases
A reaction continues even after the attainment of equilibrium.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A reaction continues even after the attainment of equilibrium.
The reaction proceeds in forward as well as reverse direction. When equilibrium is attained, it is dynamic in nature. The reactants are converted into products through forward reaction and the products are converted into reactants through reverse reaction.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases
The equilibrium state can be attained from both sides of the chemical reaction.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The equilibrium state can be attained from both sides of the chemical reaction.
Thus, if initially, the concentration of reactants is much higher than the equilibrium concentration and the concentration of products is much lower than the equilibrium concentration, the reaction will proceed in the forward direction till equilibrium is attained. On the other hand, if initially, the concentration of reactants is much lower than the equilibrium concentration and the concentration of products is much higher than the equilibrium concentration, the reaction will proceed in the reverse direction till equilibrium is attained.

Multiple choice chemistry chemical equilibrium equilibrium in chemical processes introduction to equilibrium chemical equilibrium and acids-bases

For hypothetical reversible reaction $\dfrac {1}{2}A _{2}(g) + \dfrac {1}{2}B _{2}(g) \rightarrow AB _{3}(g); \triangle H = -20\ KJ$ if standard entropies of $A _{2}, B _{2}$ and $AB _{3}$ are $60, 40$ and $50\ JK^{-1} mole^{-1}$ respectively. The above reaction will be in equilibrium at

  1. $400\ K$
  2. $500\ K$
  3. $250\ K$
  4. $200\ K$
Reveal answer Fill a bubble to check yourself
A Correct answer