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Calculate Delta H for The Following Reaction 4nh3 5o2

Reviewed by Calculator Editorial Team

This calculator helps you determine the enthalpy change (delta H) for the reaction 4NH3 + 5O2 → 4NO + 6H2O using standard enthalpies of formation. The calculation is based on the difference between the sum of the products' enthalpies and the sum of the reactants' enthalpies.

How to Calculate Delta H

The enthalpy change (delta H) for a reaction is calculated by finding the difference between the sum of the standard enthalpies of formation of the products and the sum of the standard enthalpies of formation of the reactants.

To use this calculator:

  1. Enter the standard enthalpies of formation for each reactant and product in kJ/mol.
  2. Specify the stoichiometric coefficients for each compound in the reaction.
  3. Click "Calculate" to compute the delta H value.
  4. Review the result and interpretation.

Formula

The formula for calculating delta H is:

ΔH = ΣΔHf(products) - ΣΔHf(reactants)

Where:

  • ΔH = Enthalpy change for the reaction (kJ)
  • ΔHf = Standard enthalpy of formation (kJ/mol)
  • Σ = Summation of all products and reactants

Example Calculation

For the reaction 4NH3 + 5O2 → 4NO + 6H2O:

  • Standard enthalpy of formation for NH3: -45.9 kJ/mol
  • Standard enthalpy of formation for O2: 0 kJ/mol (element in standard state)
  • Standard enthalpy of formation for NO: 90.25 kJ/mol
  • Standard enthalpy of formation for H2O: -241.8 kJ/mol

The calculation would be:

ΔH = [4(90.25) + 6(-241.8)] - [4(-45.9) + 5(0)]
ΔH = [361 + (-1450.8)] - [-183.6 + 0]
ΔH = -1089.8 - (-183.6)
ΔH = -906.2 kJ

This indicates the reaction is highly exothermic, releasing 906.2 kJ of energy.

Interpreting Results

A positive delta H value indicates an endothermic reaction (absorbs energy), while a negative value indicates an exothermic reaction (releases energy). The magnitude of delta H shows the energy change per mole of reaction.

Note: Standard enthalpies of formation values can vary slightly depending on the source. Always verify values with reliable chemical databases.

FAQ

What is standard enthalpy of formation?
The standard enthalpy of formation (ΔHf) is the change in enthalpy that occurs when one mole of a compound is formed from its constituent elements in their standard states.
How do I find standard enthalpy values?
Standard enthalpy values can be found in chemical databases, textbooks, or online resources like the National Institute of Standards and Technology (NIST) Chemistry WebBook.
What units should I use for delta H?
Delta H is typically expressed in kilojoules per mole (kJ/mol) for reactions involving moles of substances.
Can delta H be negative?
Yes, a negative delta H indicates an exothermic reaction where energy is released to the surroundings.
How accurate is this calculator?
The calculator provides accurate results based on the standard enthalpy values you input. The precision depends on the accuracy of those input values.