Gas Laws Calculator
Ideal gas equation and colligative properties in one place.
Colligative tab: m = (solute/molar mass) / (solvent mass/1000); ΔTb = i·Kb·m; ΔTf = i·Kf·m; π = i·m·R·T (kPa). An aqueous solution with density 1 g/mL is assumed, so the solvent volume equals its mass in litres.
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What it does
Gas behaviour and colligative properties show up constantly in the lab, from cylinder pressure and reaction volume to the boiling point of a saline solution. Both families of calculations reduce to a handful of formulas, but unit handling is where most mistakes happen: kPa against atm, degrees Celsius against kelvin, grams of solvent against kilograms. This calculator keeps the unit conversions visible and applies the guards that matter, such as rejecting a non-positive absolute temperature or a zero solvent mass. The result is a tool that is fast for routine work yet explicit about the assumptions behind each number.
When to use it
Use the ideal gas tab to size a gas headspace, check a cylinder inventory, or find the temperature at which a known amount of gas occupies a fixed volume. Use the colligative tab to predict the freezing point of a salt solution, estimate osmotic pressure for a buffer or cell culture medium, or confirm that a cryoprotectant solution will freeze in the expected range.
FAQ
- Which value of R should I use?
- Match R to the pressure unit: 8.314 for kPa, 0.08206 for atm and 62.36 for mmHg, all with volume in litres, moles and kelvin. Mixing units is the most common source of wrong answers, so the calculator switches R automatically when you change the pressure unit.
- Why is the temperature input in degrees Celsius but the equation uses kelvin?
- The ideal gas law is defined on the absolute temperature scale, so degrees Celsius are converted by adding 273.15 before use. A temperature of 0 °C is 273.15 K, not zero; entering 0 °C with the K option would make the equation invalid and the tool returns no result.
- What does the van't Hoff factor change in the colligative tab?
- It accounts for the number of particles each formula unit produces in solution. Use 1 for a non-electrolyte such as glucose or urea, 2 for NaCl or KCl, and 3 for CaCl2 or Na2SO4. Doubling the factor doubles the calculated boiling point elevation and freezing point depression.
- Why are the boiling and freezing points fixed at 100 °C and 0 °C?
- The colligative tab assumes an aqueous solution, so the normal boiling point is 100 °C and the normal freezing point is 0 °C. For another solvent, use the calculated ΔTb and ΔTf with that solvent's own normal boiling and freezing points instead of the displayed values.