298.15
K
6.5593
kJ/mol
-23.9407
kJ/mol
-1
30.5
kJ/mol
298.15
K
6.5593
kJ/mol
-23.9407
kJ/mol
-1
30.5
kJ/mol
The Enthalpy Change Calculator determines the enthalpy change (ΔH) of a reaction given the Gibbs free energy change and entropy change. Enthalpy represents the total heat content of a system and indicates whether a reaction releases heat (exothermic, ΔH < 0) or absorbs heat (endothermic, ΔH > 0) from its surroundings.
This calculator rearranges the fundamental Gibbs equation (ΔG = ΔH - TΔS) to solve for ΔH. It is useful in bioenergetics for decomposing the driving forces of biological reactions into their enthalpic and entropic contributions, providing deeper insight into the thermodynamic mechanisms underlying biochemical processes.
Starting from the Gibbs free energy equation:
ΔG = ΔH - TΔS
Rearranging to solve for enthalpy:
ΔH = ΔG + TΔS
Where T is the temperature in Kelvin (°C + 273.15). The TΔS term represents the entropy contribution to the reaction. A negative ΔH indicates an exothermic reaction (heat released), while a positive ΔH indicates an endothermic reaction (heat absorbed).
Inputs
Results
ATP hydrolysis has ΔG = -30.5 kJ/mol at standard conditions. With a positive ΔS (increased disorder from phosphate release), ΔH = -23.9 kJ/mol, showing the reaction is both exothermic and entropy-driven.
Inputs
Results
Protein unfolding at 37°C is endothermic (ΔH = 118.6 kJ/mol) due to breaking intramolecular bonds. Despite the large entropy gain (TΔS = 108.6 kJ/mol), ΔG is still positive, meaning folded proteins are stable at this temperature.
ΔH reflects the net change in bond energies during a reaction. If more energy is released forming new bonds than is consumed breaking old ones, ΔH is negative (exothermic). In biological reactions, ΔH captures changes in hydrogen bonds, van der Waals interactions, electrostatic interactions, and covalent bonds.
Yes. If the entropy increase (TΔS) exceeds the positive ΔH, then ΔG will be negative and the reaction is spontaneous despite being endothermic. Examples include dissolving ammonium nitrate in water and ice melting above 0°C. The entropy gain drives these processes even though they absorb heat.
Decomposing ΔG reveals the driving forces of a reaction. Some reactions are enthalpy-driven (large negative ΔH), others are entropy-driven (large positive TΔS), and many are driven by both. Understanding these contributions helps predict how reactions respond to temperature changes and design better inhibitors or catalysts.
Roboculator Team
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