Thermodynamics
Enthalpy
Heat content at constant pressure. ΔH = Q_p for constant pressure processes.
Variables
HJ
Enthalpy
Total heat content
In SI units: kg·m²/s²
UJ
Internal energy
Internal energy
In SI units: kg·m²/s²
PPa
Pressure
System pressure
In SI units: kg/(m·s²)
Allowed values: greater than 0
Vm³
Volume
System volume
Allowed values: greater than 0
Derivation
H = U + PV. At constant P: dH = dU + PdV = δQ. So ΔH = Q at constant pressure.
Your notes
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Check value
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- U = 2 J (Internal energy)
- P = 3 Pa (Pressure)
- V = 4 m³ (Volume)
Result: H = 14 J
Other thermodynamics formulas with the same quantities
- Adiabatic Process (First Law) shares Pressure, Volume
- Ideal Gas Law (Kinetic Theory) shares Pressure, Volume
- Ideal Gas Law (Molecular) (Kinetic Theory) shares Pressure, Volume
- Pressure (Kinetic Theory) (Kinetic Theory) shares Pressure, Volume
- Work Done by Gas (First Law) shares Pressure
- Internal Energy (Ideal Gas) (First Law) shares Internal energy
Where this formula is listed
- Thermodynamics formulas, under First Law, alongside Work (Isothermal Process), Heat Capacity Relation and Work (Adiabatic Process).
- In the thermodynamics list it comes after Work (Adiabatic Process) and before Entropy Change.
- Thermodynamics formula sheet, one of 34 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Enthalpy formula?
Enthalpy is written H = U + PV. Heat content at constant pressure. ΔH = Q_p for constant pressure processes. It belongs to Thermodynamics, under First Law.
What are the units in H = U + PV?
In SI units, H is enthalpy, measured in kg·m²/s²; U is internal energy, measured in kg·m²/s²; P is pressure, measured in kg/(m·s²); V is volume, measured in m³.
How is the Enthalpy formula derived?
H = U + PV. At constant P: dH = dU + PdV = δQ. So ΔH = Q at constant pressure. The result is H = U + PV.