What are the conditions when enthalpy change (ΔH) is equal to the ene

1.	What are the conditions when enthalpy change (ΔH) is equal to the energy change (ΔE)?
Answer» The enthalpy (H) and energy (E) are related by H = E + pV. For a change in the state of the system, we have Initial state H₁ = E₁ + p₁V₁ Final state H₂ = E₂ + p₂V₂ Enthalpy change = ΔH = Final enthalpy - Initial enthalpy = H₂ - H₁ = (E₂ + p₂V₂) - (E₁+ p₁V₁) = (E₂ - E₁) + (p₂V₂ - p₁V₁) or, ΔH = ΔE + (p₂V₂ - p₁V₁) When there is no change in the pressure p₁ = p₂ and when there is no change in the volume V₁ = V₂. Therefore, p₁V₁ = p₂V₂ and ΔH = ΔE. That is enthalpy change (ΔH) is equal to the energy change when a chemical reaction takes place at constant pressure and at constant volume.

What are the conditions when enthalpy change (ΔH) is equal to the energy change (ΔE)?

Answer»

The enthalpy (H) and energy (E) are related by H = E + pV. For a change in the state of the system, we have

Initial state H₁ = E₁ + p₁V₁

Final state H₂ = E₂ + p₂V₂

Enthalpy change = ΔH = Final enthalpy - Initial enthalpy

= H₂ - H₁

= (E₂ + p₂V₂) - (E₁+ p₁V₁)

= (E₂ - E₁) + (p₂V₂ - p₁V₁)

or, ΔH = ΔE + (p₂V₂ - p₁V₁)

When there is no change in the pressure p₁ = p₂ and when there is no change in the volume V₁ = V₂. Therefore, p₁V₁ = p₂V₂ and ΔH = ΔE. That is enthalpy change (ΔH) is equal to the energy change when a chemical reaction takes place at constant pressure and at constant volume.

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