Processing...

`DeltaH_"rxn"^0 = DeltaH_a^0 + DeltaH_b^0 + DeltaH_c^0 + DeltaH_d^0`

Enter a value for all fields

The **Hess's Law** calculator computes the sum of enthalpy changes for a reaction based on the changes in series of steps.

**INSTRUCTIONS:** Choose units and enter the following:

- (
**ΔH**) Enthalpy change for step A of a reaction series^{0}_{a} - (
**ΔH**) Enthalpy change for step B of a reaction series^{0}_{b} - (
**ΔH**) Enthalpy change for step C of a reaction series^{0}_{c} - (
**ΔH**) Enthalpy change for step D of a reaction series^{0}_{d}

**Overall Enthalpy Change(ΔH ^{0}_{rxn}):** The calculator returns the enthalpy change in kilojoules per mole (kJ/mol). However this can be automatically converted to compatible units via the pull-down menu.

The Hess’s Law formula is a summation of enthalpy changes for a reaction. G. H. Hess published this equation in 1840 and discovered that the enthalpy change for a reaction is the same whether it occurs via one step or several steps. Hess's Law Formula is:

H^{0}_{rxn}= H^{0}_{a} + H^{0}_{b} + H^{0}_{c} + H^{0}_{d}

where:

- H
^{0}_{rxn}is the overall enthalpy change of a reaction - H
^{0}_{a}is the enthalpy change for step A of a reaction series - H
^{0}_{b}is the enthalpy change for step B of a reaction series - H
^{0}_{c}is the enthalpy change for step C of a reaction series - H
^{0}_{d}is the enthalpy change for step D of a reaction series

All inputs have default units of kilojoules per mole (kJ/mol).

If H^{0}_{rxn} is positive, then the reaction is endothermic, which means the reaction requires the absorption of heat to proceed to completion. However, if H^{0}_{rxn} is negative, then the reaction is exothermic, and the reaction proceeds to completion by generating heat.

**R - Gas Constant:**8.3144626181532 J/(K⋅mol)**Boyle's Law Calculator**: P_{1}• V_{1}= P_{2}• V_{2}**Charles Law Calculator**: V_{1}• T_{2}= V_{2}• T_{1}**Combined Gas Law Calculator**: P•V / T= k**Gay-Lussac Law:**T_{1}•P_{2}=T_{2}•P_{1}**Ideal Gas Law**: P•V = n•R•T**Bragg's Law:**n·λ = 2d·sinθ**Hess' Law:**ΔH^{0}_{rxn}=ΔH^{0}_{a}+ΔH^{0}_{b}+ΔH^{0}_{c}+ΔH^{0}_{d}**Internal Energy**: ΔU = q + ω**Activation Energy**: E_{a}= (R*T_{1}⋅T_{2})/(T_{1}- T_{2}) ⋅ ln(k_{1}/k_{2})**Arrhenius Equation**: k = Ae^{E_a/(RT)}**Clausius-Clapeyron Equation**: ln(P_{2}/P_{1}) = (ΔH_{vap})/R * (1/T_{1}- 1/T_{2})**Compressibility Factor**: Z = (p*V_{m})/(R*T)**Peng-Robinson Equation of State**: p = (R*T)/(V_{m}- b) - (a*α)/(V_{m}^{2}+ 2*b*V_{m}- b^{2})**Reduced Specific Volume**: v_{r}= v/(R* T_{cr }/ P_{c})**Van't Hoff Equation**: ΔH^{0}= R * ( -ln(K_{2}/K_{1}))/ (1/T_{1}- 1/T_{2})

Whitten, et al. "Chemistry" 10th Edition. Pp. 564