⚖️ Gibbs Free Energy – ΔG, Spontaneity & Equilibrium
Gibbs free energy (ΔG) tells us whether a chemical reaction is spontaneous, nonspontaneous, or at equilibrium. The DAT often tests your ability to:
Interpret ΔG values
Use the Gibbs equation
Link ΔG to Keq and enthalpy/entropy changes
This blog will break it all down clearly with DAT-style visuals and strategy tips.
⚙️ What Is Gibbs Free Energy?
ΔG = ΔH − TΔS
ΔG = change in Gibbs free energy
ΔH = enthalpy change
T = temperature (Kelvin)
ΔS = entropy change
🧠 Use this to determine reaction spontaneity based on thermodynamic values.
🔍 Interpreting ΔG Values
| ΔG Value | Meaning | Reaction Direction |
|---|---|---|
| ΔG < 0 | Spontaneous | Forward favored |
| ΔG > 0 | Nonspontaneous | Reverse favored |
| ΔG = 0 | Equilibrium | No net reaction |
✅ Spontaneity ≠ speed. It just means thermodynamically favorable.
🔁 ΔG, Temperature, and Signs of ΔH/ΔS
| ΔH | ΔS | ΔG at Low T | ΔG at High T | Spontaneity Condition |
|---|---|---|---|---|
| − | + | − | − | Always spontaneous |
| − | − | − | + | Spontaneous at low T |
| + | + | + | − | Spontaneous at high T |
| + | − | + | + | Never spontaneous |
✅ DAT loves this grid. Commit it to memory or use logic with the equation.
🔬 ΔG and Equilibrium Constant (Keq)
| Kₑq Value | ΔG | Favorability |
|---|---|---|
| > 1 | ΔG < 0 | Forward favored |
| = 1 | ΔG = 0 | Equilibrium |
| < 1 | ΔG > 0 | Reverse favored |
🧠 Large Kₑq → product favored → negative ΔG
📈 DAT-Style Practice Question
Q: Which of the following reactions is spontaneous at all temperatures?
A) ΔH = −, ΔS = −
✅ B) ΔH = −, ΔS = +
C) ΔH = +, ΔS = −
D) ΔH = +, ΔS = +
🎯 DAT Strategy Tips
✅ Memorize or practice applying the ΔG = ΔH − TΔS equation
✅ Remember that T is in Kelvin
✅ Know how signs of ΔH and ΔS predict spontaneity
✅ Use logic: entropy favors disorder; negative ΔH = exothermic
More practice? See kingofthecurve.org/studyscience
🚀 Call-to-Action
Want to make ΔG your best friend?
Download the KOTC App and access:
Spontaneity question banks
Visual thermodynamic maps
Mnemonics and equation breakdowns
Curve Coins and daily chemistry drills
⚡ React smarter—with KOTC.
Frequently Asked Questions (FAQs)
-
Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.
-
Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.
-
Set short-term goals, seek support from mentors, and reward yourself for small achievements.
-
Regular exercise improves focus, reduces stress, and enhances overall mental clarity.
-
KOTC offers personalized learning tools, gamification features, and adaptive question banks to help students stay on track without burnout.
