Problem 23 - Chemistry for Allied Health

Question

The forward reaction is spontaneous for a particular reversible reaction. What can you conclude about the spontaneity of the reverse reaction?

Step-by-Step Solution

Answer

The reverse reaction is non-spontaneous.

Step 1: Understanding the Principle of Spontaneity

In thermodynamics, a reaction is spontaneous if it occurs without input of additional energy from an external source. We use the concept of Gibbs free energy change (9G) to determine spontaneity.

Step 2: Identifying Gibbs Free Energy Change

A reaction is spontaneous in the forward direction if the change in Gibbs free energy (9G) is negative (9G < 0). This implies the system releases energy to its surroundings.

Step 3: Analyzing the Reverse Reaction's Gibbs Free Energy

The reverse reaction has the opposite Gibbs free energy change of the forward reaction. So, if the forward reaction's 9G < 0, then the reverse reaction will have 9G > 0.

Step 4: Conclusion about the Reverse Reaction's Spontaneity

Since the reverse reaction has 9G > 0, it is non-spontaneous. Thus, it requires an input of energy to occur.

Key Concepts

Gibbs Free Energy

Gibbs free energy is a crucial concept for understanding chemical reactions and their spontaneity. It's represented by the symbol \( G \), and its change, \( \Delta G \), during a reaction tells us whether a process is spontaneous. - If \( \Delta G < 0 \), the reaction is spontaneous in the forward direction, meaning it can occur on its own without additional energy input. This happens because the system releases free energy, making the process more favorable.- A positive \( \Delta G > 0 \) means the reaction is non-spontaneous and requires energy input to proceed. This is typical for reverse reactions when the forward reaction is spontaneous.Understanding \( \Delta G \) helps us determine the direction and feasibility of chemical processes, guiding chemists and engineers in practical applications.

Thermodynamics

Thermodynamics is a branch of physics that deals with energy changes in physical and chemical processes. It helps us understand how and why reactions occur. One of its key roles is explaining how energy is transferred within systems. - **First Law of Thermodynamics**: This law states that energy cannot be created or destroyed, only transformed from one form to another. Energy conservation is fundamental in all reactions. - **Second Law of Thermodynamics**: It highlights that every spontaneous reaction increases the overall entropy of the universe. Entropy is a measure of disorder, and systems naturally progress towards maximum entropy. These principles are essential for predicting reaction spontaneity. They also inform us about the energy flow and help calculate important thermodynamic quantities like Gibbs free energy.

Reversible Reactions

Reversible reactions are chemical reactions that can proceed in both forward and reverse directions. The concepts from thermodynamics and Gibbs free energy are vital in understanding these reactions.- In a reversible reaction, the forward and reverse processes are occurring simultaneously at a certain rate.- At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, and the concentration of reactants and products remains constant.- Spontaneity plays a key role here. If a forward reaction is spontaneous and has \( \Delta G < 0 \), the reverse reaction will be non-spontaneous with \( \Delta G > 0 \), thus requiring energy to proceed.Reversible reactions are key in many biological and industrial processes where control and directionality of reaction pathways are crucial.