Raoult's Law Calculator
Created by Kaushik RabadiyaLast updated: September 25, 2026Raoult's law instantly calculates results using n1, n2, p solm. Use the calculator above for instant answers in your browser.
Our Raoult's Law Calculator is designed for chemistry students, educators, and laboratory professionals who need to determine the vapor pressure of an ideal solution or find its component mole fractions quickly and accurately. By entering the moles of solvent, moles of solute, and pure solvent vapor pressure, this tool solves complex thermodynamic equations in seconds, helping you avoid manual arithmetic errors in your lab work.
How Raoult's Law Works
Raoult's law establishes a fundamental relationship between the vapor pressure of a solution and the concentration of its components. The core principle states that the partial vapor pressure of each component in an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution. Mathematically, this is expressed as Psol = x × P°sov, where Psol is the vapor pressure of the solution, x is the mole fraction of the solvent, and P°sov is the vapor pressure of the pure solvent. The mole fraction (x) is calculated by dividing the moles of the solvent (n1) by the total moles of both the solvent and solute combined (n1 + n2).
Worked Calculation Example
Imagine you prepare a chemical solution by dissolving 2.0 moles of a non-volatile solute (n2 = 2.0) into 8.0 moles of pure water acting as the solvent (n1 = 8.0). The vapor pressure of pure water at your target temperature is 24.0 mmHg (P°sov = 24.0). First, compute the mole fraction of the solvent: x = 8.0 / (8.0 + 2.0) = 8.0 / 10.0 = 0.80. Next, apply Raoult's law to find the solution's vapor pressure: Psol = 0.80 × 24.0 mmHg = 19.2 mmHg. Thus, adding the solute successfully lowers the vapor pressure of the mixture down to 19.2 mmHg.
Best Practices for Solution Calculations
Always ensure your mole values are in the correct units before calculating mole fractions. Double-check that your temperature conditions remain constant, as vapor pressure fluctuates significantly with thermal changes. Remember that Raoult's law applies strictly to ideal solutions and dilute mixtures; highly concentrated solutions often show deviations due to strong intermolecular forces between solute and solvent particles.
FAQs
What does Raoult's law state?
Raoult's law states that the vapor pressure of an ideal solution containing a non-volatile solute is directly proportional to the mole fraction of the solvent present in the mixture. In simpler terms, adding a solute decreases the overall vapor pressure of the liquid because fewer solvent molecules are available at the surface to escape into the gas phase.
What is the equation of Raoult's law?
The primary equation is expressed as P_sol = x * P_sov, where P_sol represents the vapor pressure of the solution, x is the mole fraction of the solvent, and P_sov is the vapor pressure of the pure solvent. Alternatively, it can be written using individual moles as P_sol = [n1 / (n1 + n2)] * P_sov, with n1 as solvent moles and n2 as solute moles.
How do I calculate mole fraction using Raoult's law?
To find the mole fraction of a solvent in a mixture, divide the number of moles of the solvent by the total number of moles of all substances combined in the solution. Once you have this dimensionless fraction, multiply it by the known vapor pressure of the pure solvent to determine the vapor pressure exerted by the mixture.
What is the vapor pressure of a solution with a mole fraction of 0.86?
To find this vapor pressure, multiply the mole fraction (0.86) by the standard vapor pressure of your pure solvent at that specific temperature. For example, if the pure solvent has a vapor pressure of 100 mmHg, the resulting solution vapor pressure would be 0.86 multiplied by 100, which equals 86 mmHg.
Formula verified against IUPAC standards — all calculations use deterministic, standards-based formulas.
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