enthalpy
An energy quantity appearing frequently in thermodynamics; symbol H, units J (joule); defined as H = U + pV, where U is internal energy, p is pressure, and V is volume. For example, for a gas at constant pressure, the total heat that must be added to raise the temperature of the gas is the sum of the increase in internal energy of the gas plus the work done in expanding against surrounding pressure, so the total heat equals the increase in H. There is no absolute zero of enthalpy, so only changes in enthalpy can be measured.
Portions of the summary below have been contributed by Wikipedia.
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| Chemical Compound | Phase (matter) | Chemical formula | Δ Hf0 in kJ/mol |
|---|---|---|---|
| Ammonia | aq | NH3 | -80.8 |
| Ammonia | g | NH3 | -46.1 |
| Sodium carbonate | s | Na2CO3 | -1131 |
| Sodium chloride (table salt) | aq | NaCl | -407 |
| Sodium chloride (table salt) | s | NaCl | -411.12 |
| Sodium chloride (table salt) | l | NaCl | -385.92 |
| Sodium chloride (table salt) | g | NaCl | -181.42 |
| Sodium hydroxide | aq | NaOH | -469.6 |
| Sodium hydroxide | s | NaOH | -426.7 |
| Sodium nitrate | aq | NaNO3 | -446.2 |
| Sodium nitrate | s | NaNO3 | -424.8 |
| Sulphur dioxide | g | SO2 | -297 |
| Sulphuric acid | l | H2SO4 | -814 |
| Silica | s | SiO2 | -911 |
| Nitrogen dioxide | g | NO2 | 33 |
| Nitrogen monoxide | g | NO | 90 |
| Water | l | H2O | -286 |
| Water | g | H2O | -242 |
| Hydrogen | g | H2 | 0 |
| Fluorine | g | F2 | 0 |
| Chlorine | g | Cl2 | 0 |
| Bromine | l | Br2 | 0 |
| Bromine | g | Br2 | +31 |
| Iodine | s | I2 | 0 |
| Iodine | g | I2 | +62 |
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