Calculator
Formula Used
Standard free energy relation:
Delta G standard = -RT ln K
Equilibrium constant relation:
K = e raised to (-Delta G standard / RT)
Nonstandard correction:
Delta G = Delta G standard + RT ln Q
R is 8.314462618 J per mole kelvin. Temperature is converted to kelvin before calculation.
Example Data Table
| Temperature | Delta G Standard | K | Meaning |
|---|---|---|---|
| 298.15 K | -5 kJ/mol | 7.51 | Products are favored. |
| 298.15 K | 0 kJ/mol | 1.00 | Reactants and products are balanced. |
| 310 K | 8 kJ/mol | 0.0448 | Reactants are favored. |
How to Use This Calculator
Select the calculation mode first. Use free energy to K when Gibbs energy is known. Use K to free energy when the equilibrium constant is known.
Enter the temperature and choose its unit. The calculator converts every temperature to kelvin. Choose the energy unit for input and final reporting.
Add a reaction quotient only when you want a nonstandard free energy correction. Leave it blank for standard state results. Press Submit to view results above the form.
Use the CSV button for spreadsheet records. Use the PDF button for a simple printable report.
Free Energy and Equilibrium Constant Guide
What This Tool Measures
This calculator connects equilibrium constant K with Gibbs free energy. It helps show whether a reaction favors products or reactants. It is useful in thermodynamics, chemistry, physics, materials work, and laboratory reports. The core idea is simple. A negative standard free energy gives a larger K. A positive standard free energy gives a smaller K.
Why Temperature Matters
Temperature changes the size of RT in the equation. Because RT appears in the denominator, the same free energy value can create a different K at another temperature. This is why the page accepts kelvin, Celsius, and Fahrenheit. The calculation always uses kelvin internally. That keeps the thermodynamic equation consistent.
Understanding the Signs
When Delta G standard is less than zero, the exponent becomes positive. K becomes greater than one. That usually means products are favored at equilibrium. When Delta G standard is greater than zero, the exponent becomes negative. K becomes less than one. That usually means reactants are favored. When Delta G standard is zero, K equals one.
Advanced Reaction Quotient Option
The optional Q field adds a nonstandard correction. This is helpful when the current mixture is not at standard conditions. The calculator uses Delta G equals Delta G standard plus RT ln Q. If Q is less than K, the reaction tends to move forward. If Q is greater than K, the reaction tends to move backward. This helps compare present conditions with equilibrium behavior.
Exporting Results
The CSV download is useful for spreadsheets, batch notes, and online records. The PDF download is useful for quick class submissions and printed worksheets. Both exports include the important thermodynamic outputs. These include temperature, standard free energy, K, ln K, and log10 K. If Q is entered, corrected free energy is also included.
Best Practice
Use reliable units before comparing results. Energy must be per mole. Temperature must be absolute in the final equation. Very large or very small K values are common. Scientific notation is normal in equilibrium work.
FAQs
What is the equilibrium constant?
It is a ratio that describes product and reactant amounts at equilibrium. A large value means products are favored. A small value means reactants are favored.
What does negative free energy mean?
Negative standard free energy means the reaction is product favored under standard conditions. It gives an equilibrium constant greater than one.
What does positive free energy mean?
Positive standard free energy means the reaction is reactant favored under standard conditions. It gives an equilibrium constant less than one.
Why must temperature use kelvin?
Thermodynamic equations require absolute temperature. Kelvin starts at absolute zero, so it fits the gas constant and logarithmic relation correctly.
Can K be negative?
No. The equilibrium constant must be greater than zero. It comes from activity or concentration ratios, so a negative value is not valid.
What is reaction quotient Q?
Q describes the current reaction mixture. It has the same form as K, but it is not limited to equilibrium conditions.
When should I enter Q?
Enter Q when you need actual free energy at current conditions. Leave it blank when you only need standard state results.
Does this handle very small K values?
Yes. Very small or large values may appear in scientific notation. That format is normal for equilibrium and free energy calculations.