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Calculate The Heat Absorbed When The Following Reaction Pro

Reviewed by Calculator Editorial Team

This calculator determines the heat absorbed or released during a chemical reaction using Hess's Law and calorimetry. It's essential for understanding reaction energetics in chemistry and thermodynamics.

How to Use This Calculator

To calculate the heat absorbed during a reaction:

  1. Enter the standard enthalpy change (ΔH°) for the reaction in kilojoules per mole (kJ/mol)
  2. Select whether the reaction absorbs or releases heat
  3. Click "Calculate" to see the result

The calculator will display the heat absorbed in kilojoules, along with an explanation of the result.

Formula

The heat absorbed (q) during a reaction is calculated using:

q = ΔH° × n

Where:

  • q = heat absorbed (kJ)
  • ΔH° = standard enthalpy change (kJ/mol)
  • n = number of moles of reactants (mol)

For reactions that release heat, the value will be negative.

Worked Example

Consider the reaction of 2 moles of hydrogen gas with 1 mole of oxygen gas to form water:

2H₂ + O₂ → 2H₂O

If the standard enthalpy change for this reaction is -483.6 kJ/mol:

q = (-483.6 kJ/mol) × 1 mol = -483.6 kJ

This means the reaction releases 483.6 kJ of heat.

Example Table

Reaction ΔH° (kJ/mol) Moles Heat (kJ)
2H₂ + O₂ → 2H₂O -483.6 1 -483.6
C + O₂ → CO₂ -393.5 2 -787.0
N₂ + 3H₂ → 2NH₃ -92.4 1 -92.4

Interpreting the Results

The heat absorbed or released indicates the energy change during the reaction:

  • Positive values mean heat is absorbed (endothermic reaction)
  • Negative values mean heat is released (exothermic reaction)
  • Larger absolute values indicate more energetic reactions

Note: These calculations assume standard conditions (25°C and 1 atm pressure). Real-world conditions may affect actual heat values.

FAQ

What units should I use for the enthalpy change?
Use kilojoules per mole (kJ/mol) for standard enthalpy changes.
Can this calculator handle multiple reactions?
No, this calculator is designed for single reactions. For multiple reactions, use Hess's Law separately.
What if the reaction doesn't go to completion?
The calculator assumes complete reaction. For partial reactions, adjust the moles accordingly.
How accurate are the results?
The results are based on standard enthalpy values and assume ideal conditions.
Can I use this for biological reactions?
Yes, but be aware that biological systems often have different conditions than standard lab conditions.