Exergonic vs. Endergonic Reactions: Energy Flow Explained
Exergonic reactions release energy; endergonic reactions absorb energy. Both involve breaking and making chemical bonds, but the net flow of energy is opposite.
People confuse them because “endo” and “exo” sound alike and both describe energy changes. Think of exergonic as a battery powering your phone (energy out) and endergonic as charging it (energy in).
Key Differences
Exergonic reactions have negative ΔG and occur spontaneously, releasing heat or light. Endergonic reactions have positive ΔG and require energy input, often coupled to exergonic ones in cells.
Which One Should You Choose?
You don’t choose; cells use both. Exergonic drives ATP formation; endergonic builds proteins. Together they balance metabolism and keep you alive.
Examples and Daily Life
Burning wood is exergonic; photosynthesis is endergonic. Your muscles fire with exergonic ATP hydrolysis, then recharge with endergonic ATP synthesis.
Is cellular respiration exergonic or endergonic?
Exergonic; glucose is broken down, releasing energy to make ATP.
Why must endergonic reactions be coupled?
They need an external energy source; coupling with exergonic reactions supplies that energy.