intro
Question 1:
In which order of reaction does the unit of the rate constant match the unit of the rate of reaction?
Topic: Reaction Order and Rate Constants
Correct Answer: D) Zero
- The rate constant (k) and the rate of reaction (r) are crucial parameters when studying chemical reactions.
- The units of these two parameters can sometimes match, which is unique to a particular order of reaction.
- Order of reaction refers to the power to which its concentration term in the rate equation is raised.
- For example, in a reaction where A and B are reactants, if the rate constant k has the same unit as the rate of reaction r, it signifies that the total order of the reaction is zero.
- Therefore, the correct answer is D, "Zero".
Question 2:
What greatly boosts the catalytic activity of enzymes?
Topic: Enzyme Catalysis
Correct Answer: A) Coenzyme
- Enzymes are biological catalysts that speed up reactions in cells.
- Their activity is often magnified by certain substances.
- A coenzyme is an organic non-protein compound that binds with an enzyme to catalyze a reaction, enhancing its catalytic activity.
- Thus, the correct answer is A, "Coenzyme".
Question 3:
For a specific reaction, how does the rate constant change with the reactant's concentration?
Topic: Rate Constants in Chemical Reactions
Correct Answer: D) Doesn’t change
- The rate constant (k) is an essential parameter in chemistry that describes the speed of a reaction.
- Despite changes in the concentration of the reactants, the rate constant remains the same for a given reaction under constant conditions.
- Therefore, the answer is D, "Doesn’t change".
Question 4:
Given the reaction rate formula, rate = k [A][B]2, what can we infer about the reaction order?
Topic: Reaction Orders in Chemistry
Correct Answer: D) All are correct
- In a rate equation, the sum of the exponents of the concentration terms gives the overall order of the reaction.
- In the given rate equation, the reaction is first order with respect to A, as there's no exponent indicating otherwise.
- The reaction is second order with respect to B, as evidenced by the square of B's concentration.
- Adding both orders, we find that the overall reaction order is three.
- Hence, all options A, B, and C are correct, making D, "All are correct", the right answer.
MCQs 5:
In the reaction 2NO(g) + Cl2(g) ⇌ 2NOCl(g), when the concentration of Cl2 is doubled, the reaction rate doubles. When the concentration of NO(g) is doubled, the reaction rate quadruples. What is the reaction order?
Topic: Reaction Order in Chemistry
Correct Answer: C) 3
- The order of a reaction is the sum of the powers to which the concentration terms are raised in the rate equation.
- In this scenario, the rate doubles when the concentration of Cl2 doubles, indicating that the reaction is first order with respect to Cl2.
- The rate quadruples when the concentration of NO(g) doubles, indicating that the reaction is second order with respect to NO(g).
- Adding the orders, we get a total reaction order of 3, making the correct answer C, "3".
MCQs 6:
How does the activation energy change when a catalyst is used for a reaction?
Topic: Catalysts and Activation Energy
Correct Answer: B) Decreased
- A catalyst is a substance that accelerates a chemical reaction without being consumed in the process.
- It lowers the energy barrier that reactants must overcome to form products, hence reducing the activation energy.
- Therefore, the correct answer is B, "Decreased".
MCQs 7:
What is the rate of a zero-order reaction independent of?
Topic: Zero-Order Reactions
Correct Answer: B) Concentration of reactants
- Zero-order reactions are unique in that their rate is independent of the concentration of the reactants.
- This means that changing the concentration of the reactants has no effect on the rate of the reaction.
- Therefore, the answer is B, "Concentration of reactants".
MCQs 8:
Consider a reaction P + Q ⟶ R + S, which is said to be zero-order in relation to the substance P. What does this imply?
Topic: Zero-Order Reactions with Respect to Reactants
Correct Answer: D) The reaction rate does not depend on the concentration of P
- A reaction's order is determined by how the reaction rate is impacted by changes in the concentration of the reactants.
- A zero-order reaction with respect to a reactant suggests that the reaction rate remains unchanged regardless of changes in the concentration of that reactant.
- Therefore, from the options provided, D, "The reaction rate does not depend on the concentration of P", is the correct answer.
Question 9:
In a reaction that unfolds through a sequence of stages, what dictates the overall reaction rate?
Topic: Rate-Determining Step in a Reaction
Correct Answer: B) The slowest step
- When a reaction takes place over several steps, the overall reaction rate is often controlled by the slowest step, also known as the rate-determining step.
- This implies that the speed of the reaction is limited to the speed of this slowest step.
- Hence, the correct answer is B, "The slowest step".
Question 10:
If the rate of a reaction is expressed as Rate = k[A][B], how does a second-order reaction behave if [A] is in high excess?
Topic: Pseudo First Order Reactions
Correct Answer: D) The reaction becomes pseudo first order
- In a pseudo first order reaction, the concentration of one reactant is so large relative to the other that it remains virtually constant.
- This makes the reaction appear to be first order, despite being second order when both reactant concentrations are comparable.
- Therefore, the correct answer is D, "The reaction becomes pseudo first order".
Question 11:
The units of the rate constant for first and zero-order reactions, when considering molarity M, are respectively:
Topic: Rate Constant Units for Different Order Reactions
Correct Answer: A) s-1, M⋅s-1
- The units of the rate constant vary depending on the order of the reaction.
- For a first-order reaction, the unit is s-1, as the rate is directly proportional to the concentration of the reactant.
- For a zero-order reaction, the unit is M⋅s-1 as the rate does not change with the concentration of the reactant.
- Therefore, the correct answer is A, "s-1, M⋅s-1".
Question 12:
Which statement is true regarding the activated complex?
Topic: Characteristics of the Activated Complex
Correct Answer: B) It possesses maximum energy
- The activated complex is a transitional structure that forms during a chemical reaction.
- This structure is typically unstable, has a high energy, and short-lived.
- It has the maximum energy which is equivalent to the activation energy of the reaction.
- Hence, the correct answer is B, "It possesses maximum energy".
Question 13:
If a reaction takes place such that the order of the reaction is unaffected by the concentration of the reactants, the overall order of the reaction would be:
Topic: Order of a Zero-Order Reaction
Correct Answer: D) None of these
- The order of a reaction is determined by the effect the concentration of the reactants has on the reaction rate.
- If changes in the concentration of the reactants don’t affect the reaction rate, then the reaction is zero-order.
- Thus, the correct answer is D, "None of these", as the reaction is zero-order.
Question 14:
Which order of reaction is represented by the equation t1/2 = 1/ka?
Topic: Order of Reaction and Half-Life
Correct Answer: D) Second order
- The half-life of a reaction (t1/2) refers to the time taken for the concentration of a reactant to decrease by half.
- The equation t1/2 = 1/ka represents a second order reaction, in which the half-life is inversely proportional to the initial concentration of the reactant.
- Therefore, the correct answer is D, "Second order".
Question 15:
What is the order of the photosynthesis reaction?
Topic: Order of Photosynthesis Reaction
Correct Answer: C) Zero order
- Photosynthesis is a biochemical reaction which converts light energy into chemical energy.
- Since the rate of the photosynthesis reaction is independent of the concentration of the reactants, it is considered a zero order reaction.
- Therefore, the correct answer is C, "Zero order".
Question 16:
Which equation is represented by k = Ae–Ea/RT?
Topic: Understanding Reaction Rate Constant Equation
Correct Answer: C) Arrhenius equation
- The Arrhenius equation, k = Ae–Ea/RT, describes how the rate constant (k) of a reaction depends on the temperature T and the activation energy Ea.
- An increase in temperature or a high activation energy can affect the value of the rate constant.
- Thus, the correct answer is C, "Arrhenius equation".
Question 17:
In a gaseous reaction represented by the equation 2x + y ⟶ z, if the pressure in the reaction vessel is doubled while the temperature remains constant, by what factor does the rate of reaction increase?
Topic: Effect of Pressure on Reaction Rate
Correct Answer: D) 8
- The rate of a gaseous reaction is directly proportional to the concentration (or pressure) of the reactants.
- So, if the pressure is doubled, the concentration of the reactants (x and y) also doubles.
- In the reaction 2x + y ⟶ z, the rate of reaction is represented by R α [x]²[y].
- When pressure (and thus concentration) is doubled, the new rate becomes R' α [2x]²[2y] = 8R α [x]²[y].
- Thus, the rate of reaction increases by a factor of 8.
Question 18:
Which is the correct expression of the Arrhenius equation?
Topic: The Arrhenius Equation
Correct Answer: D) k = Ae-Ea/RT
- The Arrhenius equation describes how the rate constant (k) of a reaction varies with the temperature (T) and the activation energy (Ea).
- The correct form of the Arrhenius equation is k = Ae-Ea/RT, where A is the pre-exponential factor and R is the universal gas constant.
Question 19:
If the rate equation of a reaction 2A + B ⟶ product is rate = k [A]²[B], and reactant A is present in large excess, what is the order of the reaction?
Topic: Determining Order of a Reaction
Correct Answer: A) 1
- The order of a reaction is determined by the power to which the concentration of the reactants are raised in the rate equation.
- In a reaction where one of the reactants (A in this case) is in large excess, its concentration does not substantially change during the reaction, thus its effect on the rate of the reaction is negligible.
- Therefore, the rate equation simplifies to rate = k [B], making the reaction first order with respect to B.
Question 20:
As a chemical reaction progresses, how does the rate of reaction change?
Topic: Dynamics of Reaction Rate
Correct Answer: B) It decreases
- The rate of a reaction is directly proportional to the concentration of the reactants.
- As a reaction progresses, the concentration of the reactants decreases.
- Therefore, the rate of reaction decreases as the reaction proceeds.
Question 21:
The rate law for the reaction R – X + H2O → R – OH + HX is given as rate = k [R – X]. When will the rate of reaction be doubled?
Topic: Effect of Concentration on Reaction Rate
Correct Answer: D) None of these
- The rate of the reaction is proportional to the concentration of R – X.
- Doubling the concentration of R – X, not H2O, will double the rate of the reaction.
- Neither halving the concentration of R – X nor doubling the concentrations of both R – X and H2O will double the rate of reaction.
Question 22:
For the reaction A + 2B → C + D, if the active mass of A is kept constant and the active mass of B is tripled, by what factor will the rate of reaction change?
Topic: Influence of Active Mass on Reaction Rate
Correct Answer: D) Nine times
- The rate of a reaction is proportional to the reactant concentrations raised to their stoichiometric coefficients.
- For the given reaction, the rate is proportional to [A]*[B]².
- If the active mass of A is kept constant and that of B is tripled, the rate would be proportional to [A]*[3B]² = 9[A][B]².
- Hence, the rate of reaction increases by a factor of 9.
Question 23:
Which of the following is not a physical method used to determine the rate of a reaction?
Topic: Methods of Determining Reaction Rates
Correct Answer: D) Titrimetry
- Spectrometry, refractrometry, and electrical conductivity are all physical methods used to determine the rate of a chemical reaction.
- These methods typically involve measuring a physical change, such as color or electrical current, that occurs as the reaction proceeds.
- Titrimetry, on the other hand, is a chemical method for finding the rate of reaction, as it involves a process of chemical reaction.
MCQs 24:
What method can be employed to define the order of a reaction?
Topic: Determining the Order of a Reaction
Correct Answer: D) All of these
- The order of a reaction can be determined by using several methods, including the differential method, graphical method, and half-life method.
- The differential method involves comparing the rate of change of reactant concentration to the rate of change of the reaction.
- The graphical method plots concentration against time, and the slope of the resulting curve helps determine the order.
- The half-life method involves measuring the time it takes for half of the reactant to be consumed.
- Therefore, all of these methods can be used to determine the order of a reaction. The correct answer is D, "All of these".
MCQs 25:
What factor influences the rate of a reaction?
Topic: Factors Influencing Reaction Rate
Correct Answer: A) Molar concentration
- According to the law of mass action, the rate of a reaction is directly proportional to the molar concentration of the reactants.
- This is because as the concentration of the reactants increases, there are more molecules present to undergo the reaction, and thus the rate increases.
- Atomic mass or equivalent mass, on the other hand, have no direct influence on the rate of a reaction.
- Therefore, the correct answer is A, "Molar concentration".
MCQs 26:
What is the unit of the rate constant for a zero order reaction?
Topic: Units of Rate Constants in Zero Order Reactions
Correct Answer: B) mol dm⁻³ s⁻¹
- For a zero order reaction, the rate of the reaction (Rate) is directly equal to the rate constant (k).
- Since the rate of reaction is typically given in units of mol dm⁻³ s⁻¹, the rate constant for a zero order reaction would also have the same units.
- Thus, the correct answer is B, "mol dm⁻³ s⁻¹".
MCQs 27:
What is the rate equation if a reaction involves two molecules of 'A' and one molecule of 'B'?
Topic: Determining Rate Equations
Correct Answer: A) Rate = k [A]²[B]
- The rate equation of a reaction depends on the stoichiometry of the reactants.
- In a reaction where two molecules of 'A' and one molecule of 'B' are involved, the rate of the reaction would be proportional to the square of the concentration of 'A' and the concentration of 'B'.
- Therefore, the rate equation is represented as Rate = k [A]²[B].
- The correct answer is A, "Rate = k [A]²[B]".
MCQs 28:
What is the order of reaction in 'B' for the rate equation, rate = k [A]2?
Topic: Order of Reaction in 'B'
Correct Answer: D) None of These
- The rate equation, rate = k [A]2, shows that the concentration of reactant 'B' does not affect the reaction rate.
- This means that the order of reaction in 'B' is zero.
- Therefore, the correct answer is D, "None of These".
MCQs 29:
What does the order of the reaction become if the half-life of the reaction is halved when the initial concentrations of reactants are doubled?
Topic: Dependence of Reaction's Half-life on Reactant Concentration
Correct Answer: C) Second order
- The half-life of a reaction is the time it takes for the concentration of the reactant to reduce to half its original value.
- For second order reactions, the half-life is inversely related to the initial concentration of the reactants. This means that if the initial concentration is doubled, the half-life becomes half.
- Thus, if the half-life of the reaction becomes half when the initial concentrations of reactants are doubled, the order of the reaction would be second order.
- Therefore, the correct answer is C, "Second order".
MCQs 30:
What is the reason for the rate of reaction doubling with a 10°C increase in temperature?
Topic: Temperature Effects on Reaction Rates
Correct Answer: D) Increase in the number of effective collisions
- According to the collision theory, the rate of a reaction is directly proportional to the number of effective collisions between reactant molecules.
- With an increase in temperature, the kinetic energy of the molecules increases, leading to more frequent and more energetic collisions.
- Therefore, when the temperature is increased by 10°C, the number of effective collisions almost doubles, which leads to a corresponding increase in the rate of reaction.
- Hence, the correct answer is D, "Increase in the number of effective collisions".