intro
Question 1:
What methods can be used to determine the first-order reaction?
Topic: Methods for Determining First-Order Reactions
Correct Answer: D) All of the above
- The first-order reaction can be resolved by several methods. Each method listed in the options is a valid approach.
- The 'Differential Method' involves the utilization of rate expressions and integrating rate laws to determine the order of a reaction.
- In the 'Graphical Method', we plot the concentration of the reactant as a function of time to estimate the order of the reaction. The shape of the graph helps in determining the order.
- The 'Half-life Method' employs the time taken for the concentration of the reactant to reduce to half its initial value.
- All of these methods are valid ways to determine a first-order reaction, making the correct answer D, "All of the above".
Question 2:
How is optical activity measured?
Topic: Measurement of Optical Activity
Correct Answer: C) Polarimeter
- Optical activity is a property of substances to rotate the plane of polarization of light.
- Among the listed options, the 'Polarimeter' is the instrument specifically designed to measure this property.
- A 'Spectrometer' is generally used for measuring properties of light over a specific portion of the electromagnetic spectrum, but it's not specifically designed to measure optical activity.
- Similarly, 'Photometer' and 'Refractometer' have their specific uses, which are different from measuring optical activity.
- Therefore, the correct answer is C, "Polarimeter".
Question 3:
What is the process called in which the product formed acts as a catalyst?
Topic: Types of Catalysis
Correct Answer: A) Autocatalysis
- In a chemical reaction, a catalyst is a substance that can increase the reaction rate without undergoing permanent chemical change itself.
- 'Autocatalysis' is a specific type of catalysis where one of the products of the reaction acts as a catalyst for the reaction.
- 'Enzyme catalysis', 'Negative catalysis', and 'Inhibition' are other types of catalysis processes, but they do not involve the product of the reaction acting as a catalyst.
- Hence, the correct answer is A, "Autocatalysis".
Question 4:
The velocity constant or rate constant is equal to the rate of reaction when the concentrations of reactants are:
Topic: Rate Constants in Chemical Reactions
Correct Answer: B) Unity
- In chemical kinetics, the rate constant, also known as the velocity constant, is a proportionality constant in the rate equation that connects the rate of a reaction with the concentrations of the reactants.
- By definition, the rate constant is equal to the rate of reaction when the concentrations of all reactants are one, often referred to as 'Unity'.
- Therefore, the correct answer is B, "Unity".
Question 5:
A scientist discovers a compound that can exist in two forms: a powder and a crystalline structure. Both forms react with sulfuric acid. What can be predicted about their reactions?
Topic: Rate of Chemical Reactions
Correct Answer: A) The powdered form reacts more quickly.
- In chemical reactions, the rate of reaction is influenced by the surface area of the reactants.
- A powdered form of a substance has a larger surface area compared to its crystalline form.
- This increases the number of effective collisions per unit time, leading to a higher rate of reaction.
- Therefore, the correct answer is A, "The powdered form reacts more quickly".
Question 6:
What happens to the rate of a reaction if the concentration of the reactants increases?
Topic: Factors Affecting Rate of Reactions
Correct Answer: A) The rate of reaction increases.
- The rate of reaction is directly proportional to the concentration of the reactants. This relationship is expressed in the rate equation: Rate = k[A][B], where [A] and [B] are the molar concentrations of the reactants.
- So, if the concentration of the reactants increases, the rate of the reaction will also increase.
- Hence, the correct answer is A, "The rate of reaction increases".
Question 7:
What increases the rate of a reaction but is not consumed in the reaction?
Topic: Role of Catalysts in Chemical Reactions
Correct Answer: B) Catalyst
- A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy.
- It is not consumed in the reaction and remains chemically unchanged at the end of the reaction.
- A promoter enhances the activity of a catalyst, and an inhibitor slows down the reaction. Neither of these fits into the provided definition.
- Therefore, the correct answer is B, "Catalyst".
MCQs 8:
What is the field of study that focuses on the rates of chemical reactions?
Topic: Fields of Chemistry
Correct Answer: D) Reaction kinetics
- Thermochemistry studies heat changes in chemical reactions.
- Electrochemistry is concerned with reactions involving electric charges.
- Physical chemistry uses concepts of physics to explain chemical phenomena.
- Reaction kinetics specifically deals with the rates of chemical reactions.
- Thus, the correct answer is D, "Reaction kinetics".
MCQs 9:
Which substance is used as a negative catalyst during the ignition of petrol in a car engine?
Topic: Catalysts in Combustion
Correct Answer: D) TEL
- A negative catalyst, or inhibitor, slows down a chemical reaction.
- In car engines, TEL (Tetraethyllead) is used to prevent pre-ignition or "knocking" of petrol, acting as a negative catalyst.
- CO, Arsenic, and N2O5 are not typically used for this purpose.
- Hence, the correct answer is D, "TEL".
MCQs 10:
In a reaction that occurs in multiple steps, what is the slowest step called?
Topic: Reaction Steps in Chemistry
Correct Answer: B) Rate determining step
- In multi-step reactions, each step has a different speed.
- The slowest step determines the overall rate of the reaction, hence it's called the "Rate determining step".
- The "Mechanism determining step" and "Order determining step" are not standard terms used in this context.
- Thus, the correct answer is B, "Rate determining step".
MCQs 11:
What remains chemically unaltered in a catalyst during a reaction?
Topic: Characteristics of Catalysts
Correct Answer: B) Chemical composition
- A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed in the process.
- While the physical state, appearance, and surface area of a catalyst might be affected in the process, its chemical composition remains the same.
- Therefore, the correct answer is B, "Chemical composition".
MCQs 12:
What represents the rate of reaction when the concentrations of the reactants are unity?
Topic: Reaction Rate Constants
Correct Answer: C) R = k
- The rate of a reaction is given by the rate equation, R = k[A]a[B]b, where [A] and [B] are the molar concentrations of the reactants.
- When the concentrations of the reactants are unity, the rate equation simplifies to R = k.
- Thus, the correct answer is C, "R = k". This is known as the specific rate constant.
MCQs 13:
Which of the following does not influence the rate of a reaction?
Topic: Factors Affecting Reaction Rates
Correct Answer: B) Molecularity
- Several factors affect the rate of a reaction, including the concentration of reactants, the presence of a catalyst, and the temperature.
- Molecularity, on the other hand, refers to the number of molecules involved in a step of a reaction mechanism. It is related to the balanced chemical equation but doesn't have a direct effect on the rate of the reaction.
- Hence, the correct answer is B, "Molecularity".
MCQs 14:
In the rate equation, what term is represented by the sum of the exponents of the concentration terms?
Topic: Terms in the Rate Equation
Correct Answer: B) Order of Reaction
- The rate equation has the form R = k[A]a[B]b, where a and b are the exponents of the concentration terms, and they represent the order of reaction with respect to each reactant.
- The sum of these exponents gives the overall order of the reaction.
- Therefore, the correct answer is B, "Order of Reaction".
Question 15:
Who was the scientist credited with coining the term "catalysis"?
Topic: History of Catalysts
Correct Answer: D) Berzelius.
- The term "catalysis" was first introduced by a Swedish chemist.
- Neither Rutherford, Graham, nor Moseley are associated with this term.
- The credit for the term "catalysis" goes to J. Berzelius.
- Hence, the correct answer is D, "Berzelius".
Question 16:
Which of the following statements about the order of reactions is accurate?
Topic: Order of Reactions
Correct Answer: D) i, ii, and iii only.
- The order of a reaction can vary widely.
- It can be zero, implying the rate of the reaction is independent of the concentration of the reactant.
- It can also be a fraction, which is often seen in complex reactions.
- In certain cases, it can even be negative, suggesting that the rate decreases as concentration increases.
- Therefore, all statements (i, ii, iii) are correct, making the answer D, "i, ii, and iii only".
Question 17:
Which of these statements accurately depicts the behavior of the reaction rate?
Topic: Reaction Rate Over Time
Correct Answer: C) The reaction rate decreases with the passage of time.
- The rate of a chemical reaction is not a fixed quantity.
- While A and D might seem correct, they only hold under certain conditions, and B is usually not true.
- In general, as reactants are consumed and turned into products over time, the reaction rate will decrease.
- Therefore, the correct answer is C, "The reaction rate decreases with the passage of time".
Question 18:
In which of the following types of reactions is the half-life period independent of the initial concentration of the reactants?
Topic: Half-Life of Reactions
Correct Answer: A) First-order reaction.
- The half-life of a reaction is the time it takes for the concentration of a reactant to reach half of its initial value.
- For a first-order reaction, this time is constant and does not depend on the initial concentration of the reactants.
- For second- and third-order reactions, the half-life does depend on the initial concentrations.
- Therefore, the correct answer is A, "First-order reaction".
Question 19:
What is the nature of the molecularity of a chemical reaction?
Topic: Molecularity of Reactions
Correct Answer: D) It is always a whole number.
- Molecularity refers to the number of molecules participating in a single step of a reaction mechanism.
- It cannot be less than 2, nor can it be zero, because at least two molecules must interact for a reaction to occur.
- Molecularity does not have fractional values since it involves whole molecules.
- Therefore, the correct answer is D, "It is always a whole number".
Question 20:
Consider the following two-step reaction:
Step 1: A + A → C + D (slow step)
Step 2: C + B → E + F (fast step)
Which of the following steps would be considered as the rate-determining step?
Topic: Rate-Determining Step
Correct Answer: A) Step 1
- The rate-determining step in a chemical reaction is the slowest step that determines the overall reaction rate.
- In the given reaction sequence, the first step is indicated as a slow step whereas the second is a fast step.
- The slower step, Step 1, will limit how fast the overall reaction can proceed.
- Therefore, the correct answer is A, "Step 1".
Question 22:
Consider a reaction that is second order with respect to the concentration of carbon monoxide. If the concentration of carbon monoxide is doubled while keeping everything else constant, what will be the effect on the rate of reaction?
Topic: Order of Reaction
Correct Answer: D) The rate will quadruple.
- In a second order reaction, the rate is proportional to the square of the concentration of the reactant.
- If the concentration of carbon monoxide is doubled, the new rate will be proportional to (2 * original concentration)^2.
- This results in a fourfold increase in the reaction rate.
- Therefore, the correct answer is D, "The rate will quadruple".
Question 23:
What are the units of the rate constant (k) for a first-order reaction?
Topic: Units of Rate Constant
Correct Answer: A) s-1
- A first-order reaction follows the rate law: Rate = k[A], where [A] is the concentration of the reactant 'A' and 'k' is the rate constant.
- The dimensions of the reaction rate are mol dm-3 s-1 and the dimensions of the concentration [A] are mol dm-3.
- To maintain dimensional homogeneity, the units of the rate constant 'k' in a first-order reaction should be s-1.
- Therefore, the correct answer is A, "s-1".
Question 24:
How does the concentration of water affect the rate of a reaction?
Topic: Dependency of Reaction Rate on Solvent Concentration
Correct Answer: B) Effectively independent
- In reactions where water acts as a solvent, its concentration is usually in excess.
- Because of this, the reaction rate does not significantly change even with alterations in water's concentration.
- Therefore, the rate of reaction continues to remain practically independent of the concentration of water.
- Hence, the correct answer is B, "Effectively independent".
Question 25:
Given the following reaction data: "A + B → Products", which order best describes this reaction?
Topic: Order of Reaction
Correct Answer: B) Second order
- The order of a reaction is determined by how the rate changes when the concentration of the reactants is altered.
- A second order reaction can either be second order overall, meaning it depends on the concentrations of two reactants, or second order in one reactant, meaning the rate depends on the concentration of one reactant to the power of two.
- Without detailed reaction data, we can't say definitively, but based on given information, the reaction appears to be second-order.
- Therefore, the most fitting answer is B, "Second order".
Question 26:
What is the correct representation of the units of the rate constant (k) for a first-order reaction?
Topic: Units of Rate Constant for a First Order Reaction
Correct Answer: A) s-1
- The rate law for a first-order reaction is given by Rate = k[A], where 'k' is the rate constant, and [A] is the concentration of the reactant.
- The dimensions of the rate are mol dm-3 s-1, and the dimensions of the concentration [A] are mol dm-3.
- To achieve dimensional harmony, the units of 'k' in a first-order reaction need to be s-1.
- Thus, the correct answer is A, "s-1".
Question 27:
Which catalyst is typically employed when hydrogenating oils?
Topic: Catalysts in Hydrogenation of Oils
Correct Answer: C) Ni
- Hydrogenation is a type of chemical reaction where hydrogen is added to a substance, often in the presence of a catalyst.
- In the hydrogenation of vegetable oils, nickel is commonly used to accelerate the reaction.
- The catalytic activity of nickel can be enhanced by using copper and tellurium.
- As a result, the correct answer is C, "Ni".