How do you calculate enthalpy change (ΔH)?

The enthalpy change (ΔH) is the amount of heat absorbed or released by a reaction at constant pressure.

How to calculate it (without using equations):

1. Using bond energies:
   • Determine how much energy is required to break the bonds in the reactants.
   • Determine how much energy is released when new bonds form in the products.
   • Subtract the energy released from the energy absorbed to find the enthalpy change.
2. Using standard enthalpies of formation:
   • Look up the standard enthalpy values for all reactants and products.
   • Compare the total energy of products with the total energy of reactants.
   • The difference gives the enthalpy change.
3. Using calorimetry (experimentally):
   • Measure the temperature change of the solution or reaction mixture.
   • Combine it with the mass and specific heat of the substance.
   • This allows calculation of the heat absorbed or released, which is the enthalpy change.

Key idea:

• If the reaction absorbs heat, it is endothermic.
• If the reaction releases heat, it is exothermic.