Boiling Point Intermolecular Forces Calculator

Calculator Inputs

Compound name

Molar mass, g/mol

Reference boiling point, °C

Reference pressure, kPa

Target pressure, kPa

Vaporization heat, kJ/mol

Dipole moment, D

Polarizability, Å³

Hydrogen bond donors

Hydrogen bond acceptors

Branching index, 0 to 100

Association factor

Ionic or network factor

Dispersion shape factor

Hydrogen bond strength factor

Uncertainty percent

Notes

Reset

Formula Used

The pressure correction uses the integrated Clausius Clapeyron equation.

1 / T2 = 1 / T1 - (R / ΔHvap) × ln(P2 / P1)

Here, T1 and T2 are in Kelvin. Pressures use the same unit. The gas constant is 8.314462618 J mol⁻¹ K⁻¹. Vaporization heat is converted from kJ/mol to J/mol.

The force score uses this empirical comparison model.

IMF Score = mass + dispersion + dipole + hydrogen bonding + association + ionic character - branching penalty

The force based boiling estimate is a trend estimate. It is best for comparing related compounds, not replacing measured data.

How To Use This Calculator

Enter the compound name and molar mass.
Add a known reference boiling point and pressure.
Enter the target pressure for the new condition.
Add vaporization heat in kJ/mol.
Enter dipole, polarizability, and hydrogen bonding data.
Choose association, ionic, and dispersion factors.
Press the calculate button.
Download the result as CSV or PDF when needed.

Example Data Table

Compound	Molar Mass	Normal Boiling Point	ΔHvap	Dominant Force
Water	18.015 g/mol	100.0 °C	40.65 kJ/mol	Hydrogen bonding
Ethanol	46.07 g/mol	78.37 °C	38.56 kJ/mol	Hydrogen bonding
Acetone	58.08 g/mol	56.05 °C	31.3 kJ/mol	Dipole attraction
Hexane	86.18 g/mol	68.7 °C	28.9 kJ/mol	London dispersion

Why Boiling Point Depends On Forces

A boiling point is not only a temperature. It is a balance point. Vapor pressure equals the outside pressure. Molecules can then leave the liquid freely. Strong attractions hold molecules together longer. Weak attractions let them escape sooner. This calculator uses that idea in two ways. It corrects a known boiling point for pressure. It also scores intermolecular forces for trend checks.

Main Intermolecular Forces

London dispersion appears in every substance. It grows with molar mass and polarizability. Dipole forces appear when charge is uneven. Hydrogen bonding is stronger. It needs hydrogen attached to nitrogen, oxygen, or fluorine. Ionic and network attractions can be much stronger. Shape also matters. A straight molecule touches neighbors better. A branched molecule often has less surface contact.

Pressure Correction

Boiling changes when pressure changes. Lower pressure lowers the boiling point. Higher pressure raises it. The calculator applies the Clausius Clapeyron relation. It uses the reference boiling point, vaporization heat, and two pressures. The result is best near the reference point. Very wide pressure changes need laboratory vapor pressure data. Still, the estimate is useful for teaching and quick planning.

Force Score Method

The force score is a comparison aid. It is not a replacement for measured data. The score combines mass, polarizability, dipole moment, hydrogen bonding, association, and ionic character. Branching reduces the score. A higher score means stronger liquid phase attraction. That usually means a higher normal boiling point. Similar compounds give the best comparisons. Water, alcohols, ketones, alkanes, and acids show different patterns.

Using The Results

Use the pressure result when you know a normal boiling point. Use the force score when you compare related compounds. Check the dominant force line first. Then review the uncertainty range. If the range is wide, do not use the estimate for safety work. Use trusted tables for design. Use this page for homework, screening, and reports. Export the table when you need records. The PDF keeps a short summary for notes. The CSV helps compare many trials. Always enter pressure units carefully. Kelvin conversion happens inside the form. Negative Kelvin values are blocked. For mixtures, treat the output as a rough guide. Mixed liquids may boil across a range.

FAQs

What does this calculator estimate?

It estimates pressure corrected boiling point and compares intermolecular force strength. The pressure result uses a reference boiling point and vaporization heat. The force score helps compare related compounds.

Why do intermolecular forces affect boiling point?

Intermolecular forces control how strongly liquid molecules attract each other. Stronger attraction usually means more heat is needed before vapor pressure reaches outside pressure.

Which pressure unit should I use?

Use kPa in the form. The reference pressure and target pressure must use the same unit. Normal pressure is commonly entered as 101.325 kPa.

What is vaporization heat?

Vaporization heat is the energy needed to convert one mole of liquid into vapor at its boiling point. The calculator uses it for pressure correction.

Is the force based boiling estimate exact?

No. It is an empirical trend estimate. It helps compare similar compounds. Use measured boiling point data for final engineering, safety, or laboratory design work.

How does branching affect boiling point?

Branching can reduce surface contact between molecules. Less contact can weaken London dispersion attraction. This often lowers boiling point among structural isomers.

When should I use the pressure corrected result?

Use it when you know a reliable reference boiling point and vaporization heat. It is most useful when the target pressure is near the reference pressure.

Can this calculator handle mixtures?

It can give a rough guide only. Mixtures may boil over a temperature range. Vapor liquid equilibrium data is better for accurate mixture calculations.