Enthalpy (H) is the total heat content of a system at constant pressure. ΔH 0 means endothermic (absorbs heat). Standard conditions: 25°C, 1 atm.

Enthalpy Calculator

From Enthalpies of Formation

ΔH°rxn = ΣΔHf°(products) - ΣΔHf°(reactants)

ΣΔHf° of Products (kJ/mol)

ΣΔHf° of Reactants (kJ/mol)

From Bond Energies

ΔH = Σ(bonds broken) - Σ(bonds formed)

Σ Bond Energies Broken (kJ/mol)

Σ Bond Energies Formed (kJ/mol)

Calorimetry (q = mcΔT)

Calculate heat from calorimeter data

Mass of Solution (g)

Specific Heat Capacity (J/g·°C)

Temperature Change ΔT (°C)

Moles of Reactant

Hess's Law (Two Steps)

ΔH_total = ΔH₁ + ΔH₂

ΔH₁ (kJ/mol)

Multiplier for Step 1

ΔH₂ (kJ/mol)

Multiplier for Step 2

Formula

ΔH°rxn = ΣΔHf°(products) - ΣΔHf°(reactants) | ΔH = Σ(bonds broken) - Σ(bonds formed) | q = mcΔT

Frequently Asked Questions

What is enthalpy?

Enthalpy (H) is the total heat content of a system at constant pressure. ΔH < 0 means exothermic (releases heat), ΔH > 0 means endothermic (absorbs heat). Standard conditions: 25°C, 1 atm.

What is Hess's Law?

Hess's Law states that the total enthalpy change of a reaction is the same regardless of the path taken. You can add, reverse, or multiply known reactions and their ΔH values to find unknown ΔH values.

What is the difference between ΔH and q?

At constant pressure, ΔH = q (heat). In calorimetry, q_solution = mcΔT measures heat gained by the solution. q_reaction = -q_solution (opposite sign). ΔH per mole = q_reaction / moles.

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