Coupled Reactions
Ethan Taylor
7 min read
Study Guide Overview
This study guide covers thermodynamically favorable and unfavorable reactions, including spontaneity based on ΔG° and K. It explains how electrolytic cells drive nonspontaneous reactions with electricity. It also details coupled reactions, using a spontaneous reaction to drive a nonspontaneous one via a common intermediate, with examples and calculations using Hess's Law. Finally, it provides practice problems and exam tips focusing on these concepts.
#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! 🔋
Electrolytic cells use electrical energy to drive nonspontaneous redox reactions. This is the reverse of what happens in a voltaic cell (battery).
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...
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