Enthalpy Calculator

Enthalpy is a measure of the total heat content of a thermodynamic system. In practical terms, the enthalpy change of a process tells you how much heat energy is absorbed from or released to the surroundings. For processes that involve a change in temperature without a change in phase, the enthalpy change is calculated using the formula Q equals m times c times delta T, where m is the mass in kilograms, c is the specific heat capacity of the substance in joules per kilogram per kelvin, and delta T is the temperature change in degrees Celsius or kelvin (the magnitude is the same for either unit). A positive result means the process is endothermic: the substance absorbs heat, and its surroundings cool down. A negative result means the process is exothermic: the substance releases heat to its surroundings. Water has an unusually high specific heat capacity of about 4184 J/kg/K, which is why it takes a long time to heat or cool compared with metals and most other materials. This calculator covers sensible heat changes. It does not cover phase changes (for those, use the Latent Heat Calculator) or chemical reaction enthalpies calculated from bond energies or Hess cycles. Enter the mass, the specific heat capacity (common material presets are provided), and the temperature change, and the tool returns the enthalpy change in joules and kilojoules along with the direction of heat flow.

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Substance preset

Mass m

Specific heat capacity c

J/kg/K

Temperature change ΔT

°C

41,840 J

enthalpy change (ΔH)

In kilojoules41.840 kJ

Per gram41.840 J/g

ProcessEndothermic

This calculator covers sensible heat (temperature change) only. For energy in phase changes, use the Latent Heat Calculator.

How it works

The formula is ΔH = m × c × ΔT, where m is mass in kg, c is specific heat capacity in J/kg/K, and ΔT is the temperature change in °C (or K). A positive ΔT means the substance is being heated and heat is absorbed (endothermic); a negative ΔT means the substance is cooling and heat is released (exothermic). Per-gram enthalpy is ΔH divided by the mass in grams.

Worked example

You heat 1 kg of water by 10 °C. The specific heat capacity of water is 4184 J/kg/K. Using ΔH = m × c × ΔT: ΔH = 1 × 4184 × 10 = 41,840 J (41.840 kJ). The process is endothermic (heat is absorbed by the water). Per gram: 41.840 J/g. These match the default values pre-filled in the calculator above.

Related calculators

Latent Heat Calculator: find energy for phase changes using Q = mL.
Heat Transfer Calculator: calculate rate of heat flow by conduction or convection.
Boyle's Law Calculator: explore pressure-volume relationships at constant temperature.
Energy Converter: convert joules, calories, BTU, and other energy units.

Frequently asked questions

What is the formula for enthalpy change?

For sensible heat (temperature change without phase change), the enthalpy change is calculated as delta H = m times c times delta T, where m is mass in kilograms, c is the specific heat capacity in joules per kilogram per kelvin (J/kg/K), and delta T is the change in temperature in kelvin or degrees Celsius. A positive delta T means heat is absorbed (endothermic); a negative delta T means heat is released (exothermic).

What is the specific heat capacity of water?

The specific heat capacity of liquid water is approximately 4184 J/kg/K (often rounded to 4200 J/kg/K). This is unusually high compared with most other substances, which is why water is such an effective coolant and why large bodies of water moderate climate. By comparison, iron is about 449 J/kg/K and aluminium is about 900 J/kg/K.

What is the difference between endothermic and exothermic?

An endothermic process absorbs heat from the surroundings, so the system gains energy and delta H is positive. An exothermic process releases heat to the surroundings, so the system loses energy and delta H is negative. Combustion, rusting, and neutralisation reactions are typically exothermic. Dissolving ammonium nitrate in water and photosynthesis are endothermic examples.