Question

Standard state Gibbs free energy change for isomerization reaction, cis-2-pentene \rightleftharpoons trans-2-pentene is \(-3.67 \mathrm{~kJ} / \mathrm{mol}\) at \(400 \mathrm{~K}\). if more trans-2-pentene is added to the reaction vessel, then (a) more cis-2-pentene is formed (b) additional trans-2-pentene is formed (c) equilibrium remains unaffected (d) equilibrium is shifted in the forward direction

Short answer

(a) more cis-2-pentene is formed

Step-by-step solution

Understanding Isomerization and Gibbs Free Energy

The given reaction is an isomerization from cis-2-pentene to trans-2-pentene. Gibbs free energy change (9G) of -3.67 kJ/mol indicates the reaction's tendency to favor products under standard conditions. A negative 9G suggests that the formation of trans-2-pentene is thermodynamically favored.

Applying Le Chatelier's Principle

Le Chatelier's Principle states that a system at equilibrium will adjust to counteract any changes imposed on it. Adding more trans-2-pentene perturbs the equilibrium, resulting in a shift towards the side that counteracts this change, i.e., towards the formation of more reactant (cis-2-pentene).

Key concepts

Understanding Isomerization Reactions

Isomerization is a fascinating type of chemical reaction where a compound is transformed into another compound with the same molecular formula but a different structural arrangement. In simpler words, the atoms in the molecules are rearranged without changing their total number or the types of atoms present. This can result in different physical and chemical properties despite having the same atoms present. For the isomerization of cis-2-pentene to trans-2-pentene, the molecules have the same atoms but are arranged differently in space. These isomers, the cis and the trans forms, differ in their stability and the way they pack together in space. One key factor to study in isomerization reactions is Gibbs free energy. If the Gibbs free energy change (denoted by \(\Delta G\)) for a reaction is negative, it indicates that the products (in this case, the trans isomer) are more stable under standard conditions. This stability difference is why understanding isomerization reactions is crucial in chemistry.

Exploring Le Chatelier's Principle

Le Chatelier's Principle is a cornerstone concept in chemical equilibrium. It predicts how a system at equilibrium will respond to disturbances or changes. The principle states that if a system at equilibrium experiences a change in concentration, temperature, or pressure, the system will adjust to minimize that change and re-establish equilibrium. In the context of our isomerization reaction, if more trans-2-pentene is added to the system, Le Chatelier's Principle tells us that the equilibrium will shift in the direction that opposes this addition. Therefore, the system will try to "use up" this excess trans-2-pentene by converting some of it back into cis-2-pentene. This principle is not only powerful for predicting outcomes but also for understanding how systems achieve balance and how we can influence reactions in practical applications, such as chemical manufacturing or even biological systems.

Understanding the Concept of Equilibrium Shift

The term 'equilibrium shift' refers to the movement of a reaction's equilibrium position as a response to a change in conditions according to Le Chatelier's Principle. Shifts can occur forward (towards the products) or backward (towards the reactants) depending on the adjustments made to the system. When the equilibrium in a chemical reaction is disturbed, it will shift toward the side that helps restore balance. In our isomerization case, the addition of more trans-2-pentene shifts the equilibrium in the reverse direction, fostering the production of more cis-2-pentene. This balancing act of equilibrium shifts is central to reactions involving changes in concentration, pressure, and temperature. Understanding these shifts is crucial for controlling reactions in industrial processes or natural systems where maintaining an equilibrium is essential for the intended outcomes or stability.