How this calculation works
Convert masses to moles when selected. Apply the ideal gas equation to each nonreacting component in the same volume and temperature, then distinguish dry mixture fractions from wet-pressure fractions.
Component pressure kPa = component moles × 8.314462618 × Kelvin / litres; dry pressure = sum of component pressuresA worked example
Two moles nitrogen and one mole oxygen in 10 L at 300 K produce about 748.302 kPa dry pressure. Their dry mole fractions are two thirds and one third, matching their shares of dry total pressure.
Good to know
Ideal nonreacting gases only. No real-gas, condensation, reaction or safety assessment. Vapor pressure is entered, not fetched from humidity or temperature; avoid counting that component twice.
Reference: OpenStax: gas mixtures and Dalton’s law (opens in a new tab) ↗
Compare amounts in moles
Mass shares do not generally equal mole shares because molar masses differ. In mass mode the page divides each gram amount by its supplied grams-per-mole value before pressure calculations.
In moles mode the third column is not used in the numerical conversion. Keep the quantity basis explicit when copying measurements into the rows.
The nernst cell potential calculator adds calculate an ideal cell potential from a logarithmic reaction quotient or signed dimensionless activities, keeping reaction direction and electron count explicit.
All components share volume and temperature
Each ideal partial pressure is the pressure that amount would exert in the same complete container. The components are not assigned separate fractions of the container volume in this calculation.
Absolute Kelvin temperature is required. Substituting Celsius directly into the gas equation would change the physical temperature scale and give the wrong pressure.
Dry and vapor-inclusive totals are labeled separately
The dry component pressures sum to the dry pressure. An additional entered vapor pressure increases the total, so a dry mole fraction can differ from a component’s fraction of that vapor-inclusive total.
No saturation state is inferred. If vapor has already been included as a component row, do not add it again through the separate pressure field.
Use the result with the next measurement
The Nernst cell potential calculator uses dimensionless activities in a reaction quotient. A gas pressure from this page is not automatically an activity without a specified standard-state convention.
Ideal nonreacting gases only. No real-gas, condensation, reaction or safety assessment. Vapor pressure is entered, not fetched from humidity or temperature; avoid counting that component twice.
A few questions, answered
Are mass fractions the same as mole fractions?
Not generally; convert with molar mass.
Is vapor pressure calculated from temperature?
No, it is independently entered.
What temperature unit is required?
Absolute Kelvin.