Problem 9 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

A gas ' \(X\) ' at 1 atm is bubbled through a solution containing a mixture of \(1 \mathrm{M}\) \(-\mathrm{Y}^{-}\) and \(1 \mathrm{M}-\mathrm{Z}^{-}\) at \(25^{\circ} \mathrm{C}\). If the reduction potential of \(Z>Y>X\), then. (a) \(\mathrm{Y}\) will oxidize \(\mathrm{X}\) and \(\mathrm{not} \mathrm{Z}\) (b) \(\mathrm{Y}\) will oxidize \(\mathrm{Z}\) and \(\mathrm{not} \mathrm{X}\) (c) \(Y\) will oxidize both \(X\) and \(Z\) (d) \(\mathrm{Y}\) will reduce both \(\mathrm{X}\) and \(\mathrm{Z}\)

Step-by-Step Solution

Answer

Y will oxidize X and will not oxidize Z.

Step 1: Understand the concept of reduction potential

The reduction potential of a substance is its ability to gain electrons and be reduced during a chemical reaction. A higher reduction potential means a greater tendency to gain electrons. The standard reduction potential is measured under standard conditions, which include a solute concentration of 1 M, pressure at 1 atm, and temperature at 25°C (298K).

Step 2: Analyze the given reduction potentials

In the exercise, substances are ordered by their reduction potentials as follows: Z > Y > X. This means that Z has the highest tendency to gain electrons and be reduced, followed by Y, and then X, with the lowest tendency.

Step 3: Determine the direction of oxidation and reduction

Since Y has a higher reduction potential than X, it is more likely to be reduced (gain electrons), and hence will oxidize X. However, because Z has a higher reduction potential than Y, Y cannot oxidize Z. Instead, Y is more likely to be reduced by Z. Therefore, among the given options, Y will only oxidize X.

Key Concepts

Chemical Reactions in Physical Chemistry

In the fascinating world of physical chemistry, chemical reactions are the heartbeats of scientific discovery and technological innovation. At the core of understanding these reactions is the ability to predict and explain how and why substances interact with each in the ways that they do.

Chemical reactions are governed by the laws of thermodynamics and kinetics, the former dictating whether a process can occur and the latter describing the rate at which it will happen. A reaction's feasibility is often determined by looking at changes in energy, particularly the Gibbs free energy, while the kinetics are driven by factors such as concentration, temperature, and the presence of catalysts.

In the context of the textbook problem, we can apply these principles to predict the behaviour of gas X and ions Y- and Z- in the solution. We examine how the inherent properties of the molecules dictate the direction of electron transfer in the chemical reactions.

Standard Reduction Potential

Delving into electrochemical cells, the concept of standard reduction potential becomes a crucial component. It acts like a numeric value that ranks the intrinsic electron affinity of different substances; it is, simplistically put, a measure of how strongly an entity wants to be reduced by gaining electrons.

The standard reduction potentials are determined under defined conditions: a concentration of 1M for each ion, a pressure of 1 atmosphere, and at a standard temperature of 25°C (298 K). These standard conditions help to compare different substances on a level playing field. In the problem provided, the 'standard' part of standard reduction potential is key to predicting the outcome of the interaction between the different species in solution.

Electron Gain Tendency

Understanding the concept of electron gain tendency is essential when predicting the direction of redox reactions. This tendency is reflected in the standard reduction potentials; substances with higher reduction potentials are typically stronger oxidants because they have a greater tendency to gain electrons and undergo reduction.

This behavior is central to the exercise where X, Y, and Z are ranked according to their reduction potentials (Z > Y > X), revealing their respective tendencies to gain electrons. As a result, Z is the strongest oxidant and is likely to pull electrons from Y, which in turn, is more likely to accept electrons from X. Thus, in our scenario, Y will oxidize X and not Z because Y has a stronger desire — or tendency — to gain electrons as compared to X, but not as much as Z.