Calculate enthalpy change from coefficient-weighted formation values, reaction calorimetry, average bond-energy totals, or heating/cooling without a phase change. Choose matching units and the correct system for the heat sign.

Include stoichiometric coefficients in both sums; use matching states, conditions and the selected energy basis.

Related Calculators

Delta H Formula (Heating/Cooling)

The following relation is used to estimate the enthalpy change when a substance is heated or cooled at (approximately) constant pressure, with (approximately) constant Cp and no phase change.

ฮ”H โ‰ˆ Cโ‚š ร— m ร— ฮ”T

Variables:

  • ฮ”H is the enthalpy change (joules, J)
  • Cp is the specific heat capacity at constant pressure (joules per gram per degree Celsius, J/(gยทยฐC), equivalently J/(gยทK) for temperature differences)
  • m is the mass (grams, g)
  • ฮ”T is the temperature change (ยฐC or K for temperature differences)

To calculate ฮ”H for heating/cooling, multiply the specific heat capacity by the mass and the temperature change. For phase changes (melting/boiling), use ฮ”H = mยทL instead, because ฮ”T is ~0 during the transition.

What is Delta H?

Delta H, or enthalpy change, is the amount of heat released or absorbed during a chemical reaction or phase transition at constant pressure. It is an important concept in thermodynamics and chemistry, as it describes energy changes. Enthalpy alone does not determine spontaneity; entropy and temperature also matter. A negative Delta H indicates an exothermic reaction (releases heat), while a positive Delta H indicates an endothermic reaction (absorbs heat).

How to Calculate Delta H (Heating/Cooling Method)?

The following steps outline how to estimate the enthalpy change (ฮ”H) for heating/cooling a substance (no phase change) using ฮ”H โ‰ˆ mยทCpยทฮ”T.

  1. Determine the specific heat capacity (Cp) in joules per gram per degree Celsius (J/(gยทยฐC)).
  2. Determine the mass (m) in grams (g).
  3. Determine the temperature change (ฮ”T) in ยฐC (or K for temperature differences).
  4. Use the formula: ฮ”H โ‰ˆ Cp ยท m ยท ฮ”T.
  5. Calculate ฮ”H in joules (J) (or convert to kJ if desired).
  6. Choose Heating / cooling a substance to check this example. Reaction calorimetry instead uses ฮ”H = โˆ’q_surroundings/n or +q_system/n, divided by 1000 for kJ/mol of reaction extent. Formation and bond-energy sums must include stoichiometric counts and use the selected total or molar basis.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Heat capacity (C_p) = 4.18 J/gยฐC

Mass (m) = 100 g

Temperature change (ฮ”T) = 25 ยฐC

ฮ”H โ‰ˆ (4.18 J/gยฐC)(100 g)(25 ยฐC) = 10,450 J โ‰ˆ 10.45 kJ