Coupled Reactions

#Thermodynamically Unfavorable Reactions & Coupled Reactions

#Introduction: Spontaneity and Energy

Most of the time, we talk about reactions that happen on their own—thermodynamically favorable reactions, where ΔG° < 0 and K > 1. But what about reactions that don't want to happen? These are thermodynamically unfavorable reactions (ΔG° > 0, K < 1), and they won't go without a little push. Let's explore how we can make these reactions happen.

Understanding thermodynamically favorable and unfavorable reactions is crucial, as it ties into spontaneity, equilibrium, and energy changes. Expect to see this concept in both multiple-choice and free-response questions.

#External Energy Sources

Nonspontaneous reactions need an external energy source to get going. A common source is electricity. Think of it like jump-starting a car. By using electrical energy, we can force nonspontaneous redox reactions to occur in electrolytic cells. These cells are like the opposite of batteries, using electricity to drive a reaction that wouldn't happen on its own. Imagine charging your phone—that's an electrolytic cell in action! 🔋

Caption: An electrolytic cell uses an external power source to drive a non-spontaneous redox reaction.

#Coupled Reactions: Making the Unfavorable Favorable

Another way to make nonspontaneous reactions happen is through coupled reactions. This is like using a strong reaction to pull a weaker reaction along. Coupled reactions involve a nonspontaneous reaction and a spontaneous reaction that share a common intermediate. Remember from kinetics, an intermediate is a substance pro...