Raoults Law

Calculate the vapor pressure of a solution using Raoult's law. Input the pure solvent vapor pressure and mole fraction of solvent to get a step-by-step solution.

Vapor Pressure of Pure Solvent

Mole Fraction of Solvent

Result

Please check your inputs.

Enter the vapor pressure of the pure solvent in your preferred unit (e.g., atm, mmHg, kPa). Input the mole fraction of the solvent in the solution (a number between 0 and 1). Click the "Calculate" button to run the Raoult's law calculation. View the resulting vapor pressure of the solution instantly displayed in the same unit as your input. Read the step-by-step solution below the result to see how the formula was applied and verify the math.

📖 How to Use This Tool

Enter the vapor pressure of the pure solvent in your preferred unit (e.g., atm, mmHg, kPa).

Input the mole fraction of the solvent in the solution (a number between 0 and 1).

Click the "Calculate" button to run the Raoult's law calculation.

View the resulting vapor pressure of the solution instantly displayed in the same unit as your input.

Read the step-by-step solution below the result to see how the formula was applied and verify the math.

📝 What Is Raoults Law?

Raoult's Law is a fundamental principle in physical chemistry that relates the vapor pressure of a solution to the vapor pressure of the pure solvent and the mole fraction of the solvent. It states that the partial vapor pressure of a solvent above a solution equals the product of the mole fraction of the solvent and the vapor pressure of the pure solvent. This simple yet powerful law helps predict how adding a non-volatile solute lowers the vapor pressure, which in turn affects boiling point elevation and freezing point depression.

Understanding Raoult's Law is essential for students and professionals working with colligative properties, distillation processes, and solution thermodynamics. By using this tool, you can quickly compute the vapor pressure of an ideal solution and see each algebraic step, reinforcing the concept and avoiding manual calculation errors. Whether you're studying for a chemistry exam or designing a separation process, this tool provides accurate, step-by-step results to support your learning or work.

🧮 Formula

P_solution = X_solvent × P°_solvent

Where: • P_solution = vapor pressure of the solution (same units as P°) • X_solvent = mole fraction of the solvent in the solution (value between 0 and 1) • P°_solvent = vapor pressure of the pure solvent at the same temperature

💡 Tips for Best Results

✨🔍 Always ensure the vapor pressure units are consistent — mixing mmHg and atm will give wrong results.

✨🧪 Raoult's Law applies best to ideal solutions where solvent-solute interactions are similar to solvent-solvent interactions.

✨📊 Use mole fraction, not mass fraction. If you have mass data, convert to moles first to get the correct input.

✨📝 Double-check that the mole fraction of solvent plus mole fraction of solute equals 1 — otherwise the input is invalid.

❓ Frequently Asked Questions

What exactly is Raoult's Law and when is it used?

Raoult's Law states that the vapor pressure of a solvent over an ideal solution is equal to the mole fraction of the solvent times the vapor pressure of the pure solvent. It is used to predict how adding a non-volatile solute lowers the vapor pressure, which influences boiling point elevation, freezing point depression, and distillation behavior.

Does Raoult's Law work for all solutions?

No, Raoult's Law is most accurate for ideal solutions, where intermolecular forces between different molecules are similar to those between like molecules. Real solutions may show positive or negative deviations, especially when solutes and solvents have very different polarities or hydrogen-bonding abilities.

What units should I use for vapor pressure in this tool?

You can use any consistent unit — common ones are atmospheres (atm), millimeters of mercury (mmHg), kilopascals (kPa), or torr. Just make sure the pure solvent vapor pressure and the result are interpreted in the same unit. The tool will not convert between units automatically.