12 Most VSAQ’s of Electro Chemistry and Chemical Kinetics Chapter in Inter 2nd Year Chemistry (TS/AP)

2 Marks

VSAQ-1 : What is electrolysis? Give Faraday’s first law of electrolysis.

Electrolysis is a chemical process that utilizes an electric current to drive a non-spontaneous chemical reaction. During electrolysis, a compound is broken down into its constituent elements or ions through the application of electricity.

Faraday’s First Law of Electrolysis states that the amount of chemical change, which includes the mass of a substance deposited or liberated at an electrode during electrolysis, is directly proportional to the quantity of electricity (in coulombs) passed through the electrolyte. Mathematically, it can be expressed as m ∝ Q, where m represents the mass of the substance liberated, and Q is the quantity of electricity that flows through the electrolyte. This law is essential in quantifying the relationship between the electric current, the duration of the process, and the amount of substance produced or consumed during electrolysis.

VSAQ-2 : State Faraday’s Second laws of electrolysis.

Faraday’s Second Law of Electrolysis states that the masses of substances deposited or liberated at the electrodes during electrolysis are directly proportional to their chemical equivalent weights. Mathematically, it can be expressed as m₁/m₂ = E₁/E₂, where m₁ and m₂ represent the masses of different substances, and E₁ and E₂ are their respective chemical equivalent weights. This law is crucial for understanding and predicting the quantities of substances involved in electrolysis reactions, aiding in stoichiometric calculations and determining the mass relationships in electrochemical processes.

VSAQ-3 : What is a galvanic cell or voltaic cell? Give one example.

A galvanic cell, also known as a voltaic cell, is an electrochemical cell that generates electrical energy from a spontaneous chemical reaction. It consists of two half-cells, each with an electrode and an electrolyte solution. One electrode undergoes oxidation (loses electrons), while the other undergoes reduction (gains electrons), creating an electric current that flows through an external circuit, producing electrical energy. An example of a galvanic cell is the Daniell cell, where a copper electrode is placed in a copper sulfate solution, and a zinc electrode is placed in a zinc sulfate solution. These electrodes undergo chemical reactions, leading to the production of electrical energy.

VSAQ-4 : What is metallic corrosion? Give one example.

Metallic corrosion is the gradual degradation of a metal due to chemical reactions with its environment, typically involving oxygen, moisture, or other corrosive substances. It often results in the formation of oxides or other compounds on the metal’s surface, weakening its structural integrity. An example of metallic corrosion is the rusting of iron or steel when exposed to moist air. In this process, iron reacts with oxygen and water to form iron oxide (rust), which can weaken the metal over time if not prevented or controlled.

VSAQ-5 : Define order of a reaction. Give one example.

The order of a reaction refers to the mathematical relationship between the concentration of reactants and the rate of a chemical reaction. It indicates how the rate of a reaction changes concerning the concentration of reactants. The order can be zero, first, second, or even higher.

Example: Consider a simple reaction where A and B are reactants. If the rate of the reaction is directly proportional to the concentration of A (i.e., doubling the concentration of A doubles the rate), it is a first-order reaction concerning A. Similarly, if the rate is directly proportional to the concentrations of both A and B (i.e., doubling the concentration of A or B individually doubles the rate), it is a second-order reaction with respect to A and B. The specific order of a reaction is determined experimentally and helps in understanding reaction kinetics.

VSAQ-6 : Give two examples for zero order reactions.

A zero-order reaction is a type of chemical reaction in which the rate of the reaction remains constant and is independent of the concentration of the reactant. In these reactions, the rate is determined solely by the rate constant (k) and is not influenced by changes in the concentration of the reactant. Even if the initial concentration of the reactant is altered, the rate of the reaction remains unchanged. An example of a zero-order reaction is the decomposition of hydrogen peroxide (H2O2) catalyzed by manganese dioxide (MnO2), where the rate of decomposition is solely dependent on the presence of the catalyst and is not affected by variations in the initial concentration of hydrogen peroxide.

VSAQ-7 : Give two examples for gaseous first order reactions.

In gaseous first-order reactions, the rate of the chemical reaction is directly proportional to the concentration of a gas-phase reactant. Two examples of such reactions are the decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2) gas and the radioactive decay of carbon-14 (14C) into nitrogen-14 (14N) nuclei. In the case of hydrogen peroxide decomposition, as the concentration of hydrogen peroxide decreases, the rate of decomposition also decreases linearly. Similarly, in the radioactive decay of carbon-14, the rate of decay is directly proportional to the concentration of carbon-14 nuclei, and as the concentration of carbon-14 nuclei decreases over time, the rate of radioactive decay follows first-order kinetics. These reactions are characterized by their dependence on the concentration of the reactant, which makes them relatively easy to analyze and predict mathematically.

VSAQ-8 : What are pseudo first order reactions? Give one example.

Pseudo first-order reactions are a common occurrence in chemistry, especially in reactions involving multiple reactants or complex reaction mechanisms. These reactions appear to follow first-order kinetics even though they may not be strictly first-order. This happens when one of the reactants is in large excess compared to the other, effectively keeping its concentration constant throughout the reaction. An example of a pseudo first-order reaction is the hydrolysis of acetyl chloride (CH3COCl) in the presence of water. Although the reaction involves both acetyl chloride and water, the concentration of water remains essentially constant due to its large excess, leading to a rate equation that behaves like a first-order reaction with respect to acetyl chloride concentration. This simplification allows for easier analysis and prediction of reaction rates in such cases.

VSAQ-9 : A first order reaction is found to have a rate constant, K = 5.5 x 10(-14) S(-1). Find the half life of the reaction.

The half-life (t1/2) of a first-order reaction is a crucial parameter that represents the time required for the concentration of the reactant to reduce to half of its initial value. It is calculated using the formula t1/2 = (0.693 / K), where K represents the rate constant of the reaction. In the given scenario, the rate constant (K) is determined to be 5.5 x 10(-14) S(-1). By plugging this value into the formula, we can calculate the half-life as approximately 1.26 x 10^13 seconds. This means that in a first-order reaction with a rate constant of 5.5 x 10(-14) S(-1), it would take approximately 1.26 x 10^13 seconds for the concentration of the reactant to decrease by half. Understanding the half-life of a reaction is essential in various fields of chemistry and helps in predicting reaction kinetics and stability of compounds over time.

VSAQ-10 : A reaction has a half life of 10 minutes. Calculate the rate constant for the first order reaction.

To calculate the rate constant (k) for a first-order reaction, you can use the formula $$k = \frac{-0.693}{t_{1/2}}$$ where t1/2​ is the half-life of the reaction. In this case, if the reaction has a half-life of 10 minutes, you can convert the time to seconds (since the rate constant is typically in s^(-1)), resulting in $$k \approx -0.001155 \, \text{s}^{-1}$$ This negative rate constant indicates that the concentration of the reactant decreases over time in a first-order reaction.

VSAQ-11 : A solution of CuSO4 is electrolyzed for 10 minutes with a current of 1.5 amperes. What is the mass of copper deposited at the cathode?

To calculate the mass of copper (Cu) deposited at the cathode during the electrolysis of a solution of CuSO4​, we can use Faraday’s law of electrolysis.

First, we need to find the moles of electrons (n) transferred during the electrolysis. We can use the formula $$n = \frac{I \cdot t}{F}$$ where I is the current (1.5 amperes), t is the time (10 minutes or 600 seconds), and F is Faraday’s constant (approximately 96485 C/mol).

$$n = \frac{1.5 \, \text{A} \cdot 600 \, \text{s}}{96485 \, \text{C/mol}} \approx 0.00926 \, \text{moles of electrons}$$

Next, we need to determine the molar ratio between electrons and copper ions (Cu2+) in the reaction. For each mole of electrons transferred, one mole of copper ions is reduced to copper at the cathode.

Finally, we can calculate the mass of copper deposited using the molar mass of copper (Cu), which is approximately 63.55 g/mol.

$$0.00926 \, \text{moles of electrons} \times \frac{1 \, \text{mole of Cu}}{1 \, \text{mole of electrons}} \times 63.55 \, \text{g/mole of Cu} \approx 0.59 \, \text{grams}$$

So, the mass of copper deposited at the cathode is approximately 0.59 grams.

VSAQ-12 : The standard emf of Daniel cell is 1.1V. Calculate the standard Gibbs energy for the cell reaction: Zn(s)+Cu(2+) (aq)→Zn(2+) (aq)+Cu(s)

The standard Gibbs energy change (ΔG) for the cell reaction in a Daniel cell, which is given by the equation $$Zn(s) + Cu^{2+}(aq) → Zn^{2+}(aq) + Cu(s)$$ can be calculated using the relationship between ΔG, the standard cell potential (E), and the number of moles of electrons transferred (n):

$$ΔG^\circ = -nFE^\circ$$

In this reaction, n = 2 moles of electrons are transferred, and the standard cell potential (E) is 1.1 V.

Plugging in these values, we get:

$$ΔG^\circ = -(2 \, \text{moles of electrons})(96485 \, \text{C/mol})(1.1 \, \text{V})$$

$$ΔG^\circ ≈ -211266.7 \, \text{Joules}$$

Therefore, the standard Gibbs energy change for the given cell reaction is approximately -211266.7 joules.