Skip to main content
Calcimator

Heat of Reaction Calculator

Calculate the standard enthalpy of reaction (ΔH) from formation enthalpies of reactants and products using Hess's Law.

Inputs

kJ/mol
mol
kJ/mol
mol
kJ/mol
mol
kJ/mol
mol

Results

Heat of Reaction (ΔH)

-457.2 kJ

Total Heat Released/Absorbed

457.2 kJ

Exothermic?1 (1 = yes, 0 = no)
Heat per Mole of Product-152.4 kJ/mol
How to Use This Calculator
  1. Look up the Standard Enthalpy of Formation (ΔHf) in kJ/mol for each reactant and product from NIST WebBook or CRC Handbook. Elements in their standard state have ΔHf = 0.
  2. Enter Reactant 1 ΔHf and its stoichiometric coefficient (moles in the balanced reaction equation).
  3. Enter Reactant 2 ΔHf and moles — set to 0 if there is only one reactant.
  4. Enter Product 1 ΔHf and moles, then Product 2 ΔHf and moles (set to 0 if only one product).
  5. Read the Heat of Reaction (ΔH) in kJ — negative values indicate an exothermic reaction (releases heat); positive values indicate endothermic (requires heat input).
  6. Use Total Heat Released/Absorbed to size reactor cooling or heating systems and evaluate thermal runaway risks.

How the result changes with Product 1 ΔHf

Product 1 ΔHfHeat of Reaction (ΔH)Total Heat Released/Absorbed
-800-1,270.2 kJ1,270.2 kJ
-300-270.2 kJ270.2 kJ
300929.8 kJ929.8 kJ
8001,929.8 kJ1,929.8 kJ

What each input means

Reactant 1 ΔHf
Standard enthalpy of formation for the first reactant in kJ/mol.
Reactant 1 Moles
Stoichiometric coefficient for the first reactant.
Reactant 2 ΔHf
Standard enthalpy of formation for the second reactant in kJ/mol.
Reactant 2 Moles
Stoichiometric coefficient for the second reactant.
Product 1 ΔHf
Standard enthalpy of formation for the first product in kJ/mol.
Product 1 Moles
Stoichiometric coefficient for the first product.
Product 2 ΔHf
Standard enthalpy of formation for the second product in kJ/mol.
Product 2 Moles
Stoichiometric coefficient for the second product.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Reactant 1 ΔHf = -285.8, Reactant 1 Moles = 2, Reactant 2 ΔHf = 0, Reactant 2 Moles = 1 = 8 input(s) provided
  2. Calculate Heat of Reaction
    Heat of Reaction
    -457.2 = -457.2
  3. Calculate Total Heat Released/Absorbed
    Total Heat Released/Absorbed
    457.2 = 457.2
  4. Calculate Exothermic?
    Exothermic?
    1 = 1
  5. Calculate Heat per Mole of Product
    Heat per Mole of Product
    -152.4 = -152.4

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Chemical Engineering

Energy Balance Calculator

Calculate sensible heat, latent heat, total heat duty, and power requirements for process heating and cooling operations.

Chemical Engineering

Reactor Sizing Calculator

Size CSTR and PFR reactors for first-order reactions using the design equation V = FA0·X/(−rA).

Resin & Epoxy

Exothermic Heat Calculator

Estimate the peak temperature and heat risk when pouring resin, based on volume, resin type, and ambient conditions.

Chemistry

Reaction Rate Calculator

Calculate reaction rate from rate constant, reactant concentrations, and reaction orders using the rate law equation.

Chemistry

Calorimetry Calculator

Calculate heat energy (q) from mass, specific heat capacity, and temperature change using the calorimetry equation q = mcΔT.

More in Engineering.