Standard Heat of Reaction Calculator

Standard Heat of Reaction Equation:

\[ \Delta H_{rxn} = \sum \Delta H_f(\text{products}) - \sum \Delta H_f(\text{reactants}) \]

Standard Heat of Reaction (ΔH):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Standard Heat of Reaction?

The standard heat of reaction (ΔH°) is the change in enthalpy that occurs in a chemical reaction under standard conditions. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0).

2. How Does the Calculator Work?

The calculator uses the standard heat of reaction equation:

\[ \Delta H_{rxn} = \sum \Delta H_f(\text{products}) - \sum \Delta H_f(\text{reactants}) \]

Where:

\( \Delta H_{rxn} \) — Standard heat of reaction (kJ/mol)
\( \Delta H_f(\text{products}) \) — Sum of standard heats of formation of products (kJ/mol)
\( \Delta H_f(\text{reactants}) \) — Sum of standard heats of formation of reactants (kJ/mol)

Explanation: The equation calculates the difference between the total enthalpy of the products and the total enthalpy of the reactants under standard conditions.

3. Importance of ΔH Calculation

Details: Calculating standard heat of reaction is essential for understanding reaction thermodynamics, predicting reaction spontaneity, and designing chemical processes in industry.

4. Using the Calculator

Tips: Enter the sum of standard heats of formation for products and reactants in kJ/mol. The calculator will compute the standard heat of reaction.

5. Frequently Asked Questions (FAQ)

Q1: What are standard conditions?
A: Standard conditions are typically 1 atm pressure and 25°C (298 K) for thermodynamic calculations.

Q2: Where can I find ΔHf values?
A: Standard heats of formation are tabulated in thermodynamic reference books and databases like the NIST Chemistry WebBook.

Q3: What does a negative ΔH mean?
A: A negative ΔH indicates an exothermic reaction (releases heat to surroundings), while positive ΔH indicates endothermic reaction (absorbs heat).

Q4: Does this apply to all reactions?
A: This calculation applies to reactions where all reactants and products are in their standard states. For non-standard conditions, additional corrections are needed.

Q5: How does this relate to Gibbs free energy?
A: While ΔH measures heat change, Gibbs free energy (ΔG = ΔH - TΔS) determines reaction spontaneity by also considering entropy change (ΔS).