Chemistry (School & UG)

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Chemistry (School & UG)

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The Chemistry (School & UG) category covers the fundamental to advanced concepts of Chemistry, structured to support Class 11–12 students, competitive exam aspirants, and undergraduate learners. The content emphasizes conceptual clarity, problem-solving skills, and strong alignment with NCERT and university syllabi.

In this category, you will study:

Physical Chemistry – atomic structure, thermodynamics, chemical kinetics, equilibrium, electrochemistry, and solutions
Organic Chemistry – basic principles, reaction mechanisms, hydrocarbons, functional groups, biomolecules, and polymers
Inorganic Chemistry – periodic trends, chemical bonding, coordination compounds, metallurgy, and s-, p-, d-, and f-block elements
Numerical problem-solving – formula-based calculations, mole concept, and graph-based questions
Reaction mechanisms and derivations with step-by-step explanations
Comparisons, trends, and exceptions important for exams
NCERT-based theory, supported by diagrams, tables, MCQs, assertion–reason questions, numericals, and PYQs

The content is designed to build strong foundations, improve analytical and quantitative skills, and prepare students for school examinations, competitive exams, and undergraduate assessments.

Develop a clear, logical, and application-oriented understanding of Chemistry to excel academically and confidently tackle problem-based and conceptual questions at both school and UG levels.

Analytical Techniques Inorganic Chemistry Organic Chemistry Physical Chemistry

Q. For a reaction that follows first-order kinetics, what is the relationship between the rate constant and the half-life?

A. Half-life is directly proportional to k
B. Half-life is inversely proportional to k
C. Half-life is independent of k
D. Half-life is equal to k

Solution

For first-order reactions, the half-life is inversely proportional to the rate constant (t1/2 = 0.693/k).

Correct Answer: B — Half-life is inversely proportional to k

Q. For a reaction that is first order in A and second order in B, what is the overall order of the reaction?

A. 1
B. 2
C. 3
D. 4

Solution

The overall order of a reaction is the sum of the orders with respect to each reactant. Here, it is 1 (for A) + 2 (for B) = 3.

Correct Answer: C — 3

Q. For a reaction with a negative ΔH and a positive ΔS, what can be said about the spontaneity at high temperatures?

A. The reaction is non-spontaneous.
B. The reaction is spontaneous.
C. The reaction is at equilibrium.
D. The spontaneity cannot be determined.

Solution

A negative ΔH and a positive ΔS indicate that the reaction is spontaneous at high temperatures, as ΔG will be negative.

Correct Answer: B — The reaction is spontaneous.

Q. For a reaction with a rate constant of 0.1 s^-1, what is the half-life for a first-order reaction?

A. 0.693 s
B. 6.93 s
C. 10 s
D. 0.1 s

Solution

The half-life for a first-order reaction is given by t1/2 = 0.693/k. Thus, t1/2 = 0.693/0.1 = 6.93 s.

Correct Answer: A — 0.693 s

Q. For a reaction with a rate constant of 0.5 s^-1, how long will it take for the concentration of a reactant to decrease to 25% of its initial value in a first-order reaction?

A. 1.386 seconds
B. 2 seconds
C. 4 seconds
D. 8 seconds

Solution

For a first-order reaction, the time to reach 25% of the initial concentration is t = (ln(1/0.25))/k = (ln(4))/0.5 = 2.772/0.5 = 5.544 seconds.

Correct Answer: C — 4 seconds

Q. For a reaction with an activation energy of 50 kJ/mol, what is the effect of a 10 kJ/mol increase in activation energy on the rate constant at a constant temperature?

A. Rate constant increases
B. Rate constant decreases
C. Rate constant remains the same
D. Rate constant becomes zero

Solution

An increase in activation energy decreases the rate constant according to the Arrhenius equation, k = Ae^(-Ea/RT), where an increase in Ea results in a smaller k.

Correct Answer: B — Rate constant decreases

Q. For a reaction with an activation energy of 50 kJ/mol, what is the effect of increasing the temperature on the rate constant?

A. Rate constant decreases
B. Rate constant increases
C. Rate constant remains the same
D. Rate constant becomes zero

Solution

According to the Arrhenius equation, an increase in temperature results in an increase in the rate constant, k, as it provides more energy to overcome the activation energy barrier.

Correct Answer: B — Rate constant increases

Q. For a reaction with an activation energy of 50 kJ/mol, what is the effect of increasing the temperature from 300 K to 350 K on the rate constant?

A. Rate constant decreases
B. Rate constant remains the same
C. Rate constant increases
D. Rate constant doubles

Solution

According to the Arrhenius equation, an increase in temperature generally increases the rate constant due to the exponential dependence on temperature.

Correct Answer: C — Rate constant increases

Q. For a reaction with an activation energy of 50 kJ/mol, what is the rate constant at 350 K if the rate constant at 300 K is 0.1 s^-1?

A. 0.2 s^-1
B. 0.3 s^-1
C. 0.4 s^-1
D. 0.5 s^-1

Solution

Using the Arrhenius equation, k2 = k1 * e^[-Ea/R(1/T2 - 1/T1)]. Substituting values gives k2 ≈ 0.4 s^-1.

Correct Answer: C — 0.4 s^-1

Q. For a reaction with ΔH = -120 kJ, how much heat is absorbed when 0.25 moles of reactants are converted?

A. 30 kJ
B. 60 kJ
C. 120 kJ
D. 15 kJ

Solution

Heat absorbed = ΔH * n = -120 kJ * 0.25 = -30 kJ.

Correct Answer: B — 60 kJ

Q. For a redox reaction with E° = 0.45 V and n = 3, what is the maximum work (W) obtainable from the reaction if 1 mole of reactants is used?

A. -135 kJ
B. -150 kJ
C. 135 kJ
D. 150 kJ

Solution

W = -nFE° = -3 * 96485 C/mol * 0.45 V = -130.9 kJ.

Correct Answer: C — 135 kJ

Q. For a redox reaction, if the standard reduction potentials are E°(A/B) = 0.80 V and E°(C/D) = 0.40 V, which species is the stronger oxidizing agent?

A. A
B. B
C. C
D. D

Solution

The stronger oxidizing agent is the one with the higher reduction potential. Here, A/B has a higher E° than C/D.

Correct Answer: A — A

Q. For a zero-order reaction, how does the concentration of reactant affect the rate?

A. Rate is directly proportional to concentration
B. Rate is inversely proportional to concentration
C. Rate is independent of concentration
D. Rate decreases with increasing concentration

Solution

In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.

Correct Answer: C — Rate is independent of concentration

Q. For a zero-order reaction, how does the concentration of reactant change over time?

A. Linearly with time
B. Exponentially with time
C. Inversely with time
D. Quadratically with time

Solution

In a zero-order reaction, the rate is constant, leading to a linear decrease in concentration over time.

Correct Answer: A — Linearly with time

Q. For a zero-order reaction, if the initial concentration is 0.5 M and the rate constant is 0.1 M/s, how long will it take for the concentration to drop to 0.2 M?

A. 3 s
B. 5 s
C. 7 s
D. 10 s

Solution

For a zero-order reaction, [A] = [A]0 - kt. Thus, 0.2 M = 0.5 M - (0.1 M/s)t, leading to t = (0.5 - 0.2) / 0.1 = 3 s.

Correct Answer: B — 5 s

Q. For a zero-order reaction, what is the relationship between the concentration of reactant and time?

A. Concentration decreases linearly with time
B. Concentration decreases exponentially with time
C. Concentration remains constant
D. Concentration increases with time

Solution

In a zero-order reaction, the rate is constant, leading to a linear decrease in concentration over time.

Correct Answer: A — Concentration decreases linearly with time

Q. For an ideal gas, which equation relates the change in internal energy to heat and work?

A. ΔU = Q + W
B. ΔU = Q - W
C. ΔU = W - Q
D. ΔU = Q * W

Solution

The first law of thermodynamics states that the change in internal energy (ΔU) is equal to the heat added to the system (Q) minus the work done by the system (W).

Correct Answer: B — ΔU = Q - W

Q. For the equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g), what will happen if O2 is removed?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change occurs
D. Reaction stops

Solution

Removing O2 will shift the equilibrium to the left to produce more O2, in accordance with Le Chatelier's Principle.

Correct Answer: B — Equilibrium shifts to the left

Q. For the equilibrium reaction 2NO2(g) ⇌ N2O4(g), what is the effect of increasing the temperature?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the concentration of NO2

Solution

If the reaction is exothermic, increasing the temperature will shift the equilibrium to the left, favoring the formation of reactants (NO2).

Correct Answer: B — Shifts equilibrium to the left

Q. For the equilibrium reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens if O2 is removed?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change
D. Increases the temperature

Solution

Removing O2 decreases its concentration, causing the equilibrium to shift to the left to produce more O2, in accordance with Le Chatelier's Principle.

Correct Answer: B — Equilibrium shifts to the left

Q. For the equilibrium reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens if SO3 is removed?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change in equilibrium
D. Reaction stops

Solution

Removing SO3 decreases its concentration, causing the equilibrium to shift to the right to produce more SO3 and restore balance.

Correct Answer: A — Equilibrium shifts to the right

Q. For the equilibrium reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what will happen if the volume of the container is increased?

A. Shifts to the right
B. Shifts to the left
C. No effect
D. Increases the reaction rate

Solution

Increasing the volume decreases the pressure, which shifts the equilibrium to the left, favoring the side with more moles of gas (3 moles of reactants).

Correct Answer: B — Shifts to the left

Q. For the equilibrium reaction A(g) + B(g) ⇌ C(g), if the reaction is endothermic, what is the effect of increasing pressure?

A. Shifts equilibrium to the right
B. Shifts equilibrium to the left
C. No effect on equilibrium
D. Increases the rate of the forward reaction

Solution

Increasing pressure favors the side with fewer moles of gas. If A and B have more moles than C, the equilibrium will shift to the left.

Correct Answer: B — Shifts equilibrium to the left

Q. For the equilibrium reaction A(g) + B(g) ⇌ C(g), if the temperature is decreased and the reaction is endothermic, what will happen?

A. Shift to the right
B. Shift to the left
C. No change
D. Reaction stops

Solution

Decreasing the temperature of an endothermic reaction shifts the equilibrium to the right, favoring the formation of products.

Correct Answer: A — Shift to the right

Q. For the equilibrium reaction CO(g) + 2H2(g) ⇌ CH3OH(g), what happens if the concentration of H2 is increased?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change occurs
D. Reaction rate decreases

Solution

Increasing the concentration of H2 will shift the equilibrium to the right, favoring the production of CH3OH.

Correct Answer: A — Equilibrium shifts to the right

Q. For the reaction 2NO(g) + O2(g) ⇌ 2NO2(g), if the initial concentrations are [NO] = 0.5 M and [O2] = 0.2 M, what is the equilibrium concentration of NO2 if Kc = 10?

A. 0.1 M
B. 0.2 M
C. 0.5 M
D. 0.4 M

Solution

Using the expression Kc = [NO2]^2 / ([NO]^2[O2]), we find that at equilibrium [NO2] = 0.4 M.

Correct Answer: D — 0.4 M

Q. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens if SO3 is removed from the system?

A. Shift to the left
B. Shift to the right
C. No change
D. Increase the rate of reaction

Solution

Removing SO3 decreases its concentration, causing the equilibrium to shift to the right to produce more SO3, according to Le Chatelier's Principle.

Correct Answer: B — Shift to the right

Q. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens if the pressure is increased?

A. Equilibrium shifts to the left
B. Equilibrium shifts to the right
C. No change in equilibrium position
D. Increases the temperature

Solution

Increasing the pressure will shift the equilibrium to the right, favoring the formation of SO3, as it has fewer moles of gas.

Correct Answer: B — Equilibrium shifts to the right

Q. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what is the effect of increasing the pressure?

A. Shifts equilibrium to the left
B. Shifts equilibrium to the right
C. No effect on equilibrium
D. Increases the temperature

Solution

Increasing the pressure will shift the equilibrium to the right, favoring the production of SO3, as it has fewer moles of gas (3 moles to 2 moles).

Correct Answer: B — Shifts equilibrium to the right

Q. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what will happen if the temperature is decreased?

A. Equilibrium shifts to the right
B. Equilibrium shifts to the left
C. No change occurs
D. Reaction rate decreases

Solution

Decreasing the temperature of an exothermic reaction will shift the equilibrium to the right, favoring the formation of SO3.

Correct Answer: A — Equilibrium shifts to the right

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