Calculator inputs
Choose a thermochemistry mode, enter your values, and calculate heat flow, reaction enthalpy, entropy effects, or free energy outputs.
The form uses three columns on large screens, two on tablets, and one on mobiles.
Formula used
The calculator combines several standard thermochemistry relations so you can model thermal changes, reaction energetics, and free energy behavior.
1) Sensible heat
q = m × c × ΔT
q = heat transfer, m = mass, c = specific heat capacity, ΔT = final temperature minus initial temperature.
2) Phase change heat
q = m × L
L = latent heat for fusion, vaporization, or another phase transition. The sign depends on whether energy is absorbed or released.
3) Reaction enthalpy
q = n × extent × ΔHrxn
n = moles reacting and ΔHrxn is the enthalpy change per mole of reaction.
4) Hess law
ΔHtarget = Σ(step ΔH × multiplier)
Use positive or negative multipliers to reverse or scale pathway steps.
5) Bond energy estimate
ΔH ≈ Σ(bonds broken) − Σ(bonds formed)
This is an approximation built from average bond dissociation energies.
6) Gibbs free energy
ΔG = ΔH − TΔS
When ΔG is negative, the process is spontaneous under the chosen temperature and assumptions.
How to use this calculator
- Choose the thermochemistry mode that matches your problem, such as calorimetry, Hess law, or Gibbs free energy.
- Enter the required values. Keep units consistent or select the matching unit menu beside each field.
- Click Calculate. The result card appears above the form, directly below the header section.
- Review the calculated metrics, sign conventions, and interpretation note for thermodynamic meaning.
- Use the export buttons to save the current result table as CSV or PDF.
Example data table
| Mode | Example inputs | Formula | Example result |
|---|---|---|---|
| Sensible heat | 250 g water, 4.18 J/g·K, 25°C to 80°C | q = m × c × ΔT | 57,475 J |
| Phase change | 100 g ice, 334 J/g, melting | q = m × L | 33,400 J |
| Reaction enthalpy | 2 mol, extent 1, ΔH = -285.8 kJ/mol | q = n × extent × ΔH | -571.6 kJ |
| Hess law | -393.5 and -285.8 kJ/mol, multipliers 1 | Σ(step ΔH × multiplier) | -679.3 kJ/mol |
| Bond energy | Broken 1670, formed 1850 kJ/mol | Broken − formed | -180 kJ/mol |
| Gibbs free energy | ΔH = -40 kJ/mol, ΔS = 120 J/mol·K, T = 298.15 K | ΔG = ΔH − TΔS | -75.778 kJ/mol |
Frequently asked questions
1) What does a positive heat value mean?
A positive heat value means the system absorbs energy from its surroundings. In common chemistry problems, that behavior is described as endothermic.
2) What does a negative reaction enthalpy indicate?
A negative reaction enthalpy indicates energy release. The process is exothermic, and surrounding materials usually warm unless energy is removed elsewhere.
3) Why is Hess law useful?
Hess law lets you calculate a difficult reaction enthalpy by combining simpler known reactions. Because enthalpy is a state function, pathway details do not change the total.
4) Are bond energy results exact?
No. Bond energy calculations use average dissociation values, so they provide estimates rather than exact experimental enthalpies. They remain useful for quick comparisons and predictions.
5) Why does temperature matter in Gibbs free energy?
Temperature multiplies entropy in the relation ΔG = ΔH − TΔS. A process can switch between spontaneous and nonspontaneous as temperature changes.
6) Can I use kelvin or Celsius here?
Yes. For temperature differences in sensible heat, kelvin and Celsius intervals are numerically identical. Absolute Gibbs calculations, however, require kelvin.
7) What should I enter for the extent factor?
Use the extent factor when your reaction equation is scaled beyond its base stoichiometric form. Enter 1 for the standard balanced equation amount.
8) When should I export CSV or PDF?
Use CSV for spreadsheets, data logs, and analysis workflows. Use PDF when you want a clean report for class notes, lab records, or sharing.