Use the calculator to estimate enthalpy change (ΔH) in several common ways: (1) heating/cooling a substance at (approximately) constant pressure using m·Cp·ΔT (no phase change and roughly constant Cp), (2) combining steps with Hess’s law, (3) using standard enthalpies of formation (ΔHf°), or (4) phase changes using latent heat (m·L).

Delta H Calculator

q = m·Cₚ·ΔT
Hess’s Law
From ΔHf°
Phase Change

Enter any 3 values to calculate the missing variable (heating/cooling only; no phase change)

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.

ΔH ≈ C_p * m * ΔT

Variables:

  • ΔH is the enthalpy change (Joules, J)
  • Cp is the specific heat capacity at constant pressure (Joules per gram per degree Celsius, J/(g·°C), equivalently J/(g·K) for temperature differences)
  • m is the mass (grams, g)
  • ΔT is the temperature change (°C or K for temperature differences)

To calculate ΔH for heating/cooling, multiply the specific heat capacity by the mass and the temperature change. For phase changes (melting/boiling), use ΔH = m·L instead, because ΔT 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 helps predict the energy changes and feasibility of reactions. 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 (ΔH) for heating/cooling a substance (no phase change) using ΔH ≈ m·Cp·ΔT.

  1. Determine the specific heat capacity (Cp) in Joules per gram per degree Celsius (J/(g·°C)).
  2. Determine the mass (m) in grams (g).
  3. Determine the temperature change (ΔT) in °C (or K for temperature differences).
  4. Use the formula: ΔH ≈ Cp · m · ΔT.
  5. Calculate ΔH in Joules (J) (or convert to kJ if desired).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

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

Heat capacity (C_p) = 4.18 J/g°C

Mass (m) = 100 g

Temperature change (ΔT) = 25 °C

ΔH ≈ (4.18 J/g°C)(100 g)(25 °C) = 10,450 J ≈ 10.45 kJ