Enthalpy Calculator
Calculate enthalpy (H = U + PV), enthalpy change (ΔH = ΔU + PΔV), reaction ΔH via Hess’s law, sensible enthalpy (m·c·ΔT), latent enthalpy (m·L), as well as molar & specific enthalpy — complete with an energy unit converter. All calculations run 100% on your device.
Mode 1 — Enthalpy: H = U + PV
Mode 2 — Enthalpy Change: ΔH = ΔU + PΔV
Mode 3 — Hess’s Law: Reaction ΔH
Reaktan
Produk
ΔH valuef° is the standard enthalpy of formation at 298 K (kJ/mol); pure elements = 0.
Mode 4 — Sensible Enthalpy: ΔH = m·c·ΔT
This mode computes the enthalpy change at constant pressure for heating/cooling. For full calorimetry (Black’s principle, equilibrium temperature of several bodies), use the calorimetry calculator.
Mode 5 — Latent Enthalpy: ΔH = m·L
Mode 6 — Specific, Molar Enthalpy & Energy Converter
Energy unit converter
Verified Worked Examples
| Kasus | Input | Result |
|---|---|---|
| H = U + PV | U = 5000 J; P = 1 atm; V = 20 L | H = 7026,5 J |
| ΔH = ΔU + PΔV | ΔU = 3000 J; P = 100 kPa; ΔV = 0,005 m³ | ΔH = 3500 J |
| Pembakaran metana | CH₄ + 2O₂ → CO₂ + 2H₂O(l) | ΔH = −890,36 kJ/mol (eksoterm) |
| Air 250 g, 20 °C → 80 °C | m = 250 g; c = 4,184 J/(g·K); ΔT = 60 K | ΔH = 62.760 J = 62,76 kJ = 15,00 kkal |
| Menguapkan 100 g air | m = 100 g; L = 2260 J/g | ΔH = 226.000 J = 226 kJ |
| Molar enthalpy | ΔH = 10.000 J; n = 2 mol | 5000 J/mol |
All examples above were recomputed from the formulas with high precision and match this calculator’s engine.
Metodologi & Batasan
- Modes 1–2 use the definitions H = U + PV and ΔH = ΔU + PΔV; ΔH mode assumes constant pressure.
- Mode 3 uses Hess’s law with standard enthalpy of formation values (298 K, 1 atm); pure elements = 0 kJ/mol.
- Mode 4 assumes specific heat c constant with temperature and no phase change.
- Mode 5 assumes a perfect phase change at constant temperature.
- The PV term is treated as ideal; for real fluids use appropriate thermodynamic property data.
- Konversi: 1 kal = 4,184 J; 1 BTU = 1055,06 J; 1 atm = 101325 Pa.
Frequently Asked Questions about Enthalpy
What is enthalpy?
Enthalpy (H) is a thermodynamic state function defined as H = U + PV — the sum of internal energy (U) plus the product of pressure (P) and volume (V) of the system. Its unit is the joule (J). Enthalpy represents the total energy content of the system at a given pressure.
What is the formula for computing enthalpy H = U + PV?
H = U + P × V. Example: a system with internal energy U = 5000 J, pressure P = 1 atm (101325 Pa), and volume V = 20 L (0.02 m³) has enthalpy H = 5000 + 101325 × 0.02 = 7026.5 J. Mode 1 of this calculator can also solve for U, P, or V when H is known.
What is the difference between ΔH and ΔU?
ΔH = ΔU + PΔV at constant pressure. ΔU is the change in internal energy, while ΔH also accounts for pressure–volume work. When volume shrinks (negative ΔV), the PΔV term is negative and ΔH is smaller than ΔU. At constant volume, ΔV = 0 so ΔH = ΔU.
Why does heat at constant pressure equal ΔH?
From the first law of thermodynamics, the heat absorbed/released by a system at constant pressure is exactly equal to its enthalpy change: Q_p = ΔH. That is why enthalpy is a central quantity in chemistry: lab reactions generally occur at constant atmospheric pressure.
What do negative and positive ΔH mean?
Negative ΔH means an exothermic reaction — the system releases heat to the surroundings (example: methane combustion ΔH = −890.36 kJ/mol). Positive ΔH means endothermic — the system absorbs heat (example: CaCO₃ decomposition ΔH = +178.3 kJ/mol).
How do you calculate reaction ΔH with Hess’s law?
ΔH°reaction = Σ(n × ΔHf° products) − Σ(n × ΔHf° reactants), with n the stoichiometric coefficients. Example for water formation 2H₂ + O₂ → 2H₂O(l): ΔH = 2 × (−285.83) − 0 = −571.66 kJ. Mode 3 provides a table of 22 species with standard ΔHf° values plus 5 preset reactions.
What is standard enthalpy of formation?
Standard enthalpy of formation (ΔHf°) is the enthalpy change when 1 mol of a compound forms from its elements in their standard states (298 K, 1 atm), in kJ/mol. Pure elements such as O₂, H₂, and C (graphite) are defined with ΔHf° = 0. The values used by this tool follow common standard data, e.g. H₂O(l) = −285.83 kJ/mol and CO₂(g) = −393.51 kJ/mol.
How do you calculate the enthalpy change when heating a substance (sensible enthalpy)?
At constant pressure, ΔH = m × c × ΔT. Example: heating 250 g of water from 20 °C to 80 °C with c = 4.184 J/(g·K): ΔH = 250 × 4.184 × 60 = 62,760 J = 62.76 kJ (≈ 15.00 kcal). Valid as long as there is no phase change and c is taken as constant.
How do you calculate phase-change enthalpy (latent enthalpy)?
ΔH = m × L, with L the latent heat. Example: vaporizing 100 g of water (L = 2260 J/g) requires ΔH = 100 × 2260 = 226,000 J = 226 kJ. Conversely, condensing 100 g of steam releases the same heat (negative ΔH).
What is the difference between specific and molar enthalpy?
Specific enthalpy = ΔH per unit mass (J/g), while molar enthalpy = ΔH per mole of substance (J/mol or kJ/mol). They are linked through molar mass: 1 mol of CH₄ (16.04 g) releasing 890.36 kJ means its specific enthalpy is −890.36 ÷ 16.04 ≈ −55.51 kJ/g.
What are the enthalpy units and their conversions?
The SI units are joule (J) and kilojoule (kJ). 1 cal = 4.184 J; 1 kcal = 4184 J; 1 BTU = 1,055.06 J; 1 kWh = 3.6 million J. Example: 62.76 kJ = 62.76 ÷ 4.184 = 15.00 kcal. The converter mode in this tool supports J, kJ, cal, kcal, Wh, kWh, BTU, and eV.
When do you use H = U + PV vs ΔH = ΔU + PΔV mode?
Use H = U + PV when you want the absolute enthalpy of a state from its internal energy, pressure, and volume. Use ΔH = ΔU + PΔV when you want the enthalpy change of a process from its internal-energy change and volume change — e.g. computing gas expansion work at constant pressure.
What are the limitations of this enthalpy calculator?
This tool assumes constant pressure for ΔH mode, specific heat (c) constant with temperature, no phase change in sensible mode, sufficiently ideal gas behavior for the PV term, and ΔHf° values at 298 K. For complex real processes (reactors, turbines, mixed phase changes), use appropriate thermodynamic property data.
Where can I learn more about heat and thermal equilibrium?
For pure heat calculations including Black’s principle and the thermal equilibrium temperature of several bodies, use our calorimetry calculator. For heat transfer coefficients and building heat-load calculations, see the heat transfer coefficient calculator.
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