Gibbs Free Energy Calculator
Use this calculator to compute the Gibbs free energy change (ΔG) for a process using the relation ΔG = ΔH − TΔS. Provide the enthalpy change (ΔH) in kJ/mol, the entropy change (ΔS) in J/mol·K, and the temperature (T) in Kelvin. The calculator converts units as necessary and displays results in kJ/mol or J/mol depending on your selection. Understanding Gibbs free energy is essential for predicting the spontaneity of chemical reactions and is a fundamental concept in thermodynamics.
How it Works: Understanding Gibbs Free Energy
The Gibbs free energy change indicates whether a process is spontaneous at constant temperature and pressure. A negative ΔG means the process is spontaneous, while a positive ΔG means it is non-spontaneous. The formula used is:
ΔG = ΔH − TΔSNote on units: ΔH should be entered in kJ/mol and ΔS in J/mol·K. The term TΔS is computed as (T × ΔS) which yields J/mol; it is converted to kJ/mol by dividing by 1000 so it can be subtracted from ΔH (kJ/mol).
This concept underpins various applications in chemistry, including reaction kinetics and equilibrium, making the Gibbs free energy calculator a useful tool for students and researchers alike.
Example: Calculating Gibbs Free Energy
Suppose a reaction has ΔH = −100 kJ/mol and ΔS = 50 J/mol·K at T = 298 K. Then:
TΔS = 298 K × 50 J/mol·K = 14,900 J/mol = 14.9 kJ/mol
ΔG = ΔH − TΔS = (−100 kJ/mol) − (14.9 kJ/mol) = −114.9 kJ/mol
Using the Gibbs Free Energy Calculator
- Enter ΔH in kJ/mol (can be negative for exothermic processes).
- Enter ΔS in J/mol·K.
- Enter the temperature in Kelvin.
- Optionally choose to display the result in kJ/mol or J/mol.
The calculator updates automatically as you change inputs. Click the "Download PDF" button to export the inputs and results.
FAQ: Common Questions about Gibbs Free Energy
Why is ΔS in J/mol·K and ΔH in kJ/mol?
By convention, entropy is often expressed in J/mol·K and enthalpy in kJ/mol. The calculator converts TΔS to kJ/mol so the units match when computing ΔG.
What does a negative ΔG mean?
A negative Gibbs free energy means the process is spontaneous under constant temperature and pressure.
Can I use different units?
Enter values using the units specified by the input fields. You can change the result display to J/mol if you prefer finer granularity.
Is Gibbs free energy relevant in biological systems?
Yes, Gibbs free energy is crucial for understanding metabolic reactions and processes in biochemistry. It helps predict whether reactions occur spontaneously in living organisms.
How does temperature affect Gibbs free energy?
The temperature can significantly influence the value of ΔG, especially when ΔS is positive or negative. Higher temperatures can make endothermic reactions (positive ΔH) more favorable if ΔS is also positive.