| Propellant Heats of Formation, Hydrogen Atoms, Oxygen Atoms & Densities | ||||
| Propellant | Heat of Formation ( J / kmol ) | Hydrogen | Oxygen | Density ( kg / m^3 ) |
| Water | -285,830,000 |
2 |
1 |
997.000 |
| Water at 373 K | -280,183,000 |
2 |
1 |
958.400 |
| Water at 394 K | -278,600,000 |
2 |
1 |
944.000 |
| Water at 452 K | -274,240,000 |
2 |
1 |
903.000 |
| Water at 531 K | -268,310,000 |
2 |
1 |
848.000 |
| Water at 624 K | -261,290,000 |
2 |
1 |
784.000 |
| Steam at 373 K | -239,300,000 |
2 |
1 |
0.588 |
| Steam at 394 K | -238,595,000 |
2 |
1 |
0.557 |
| Steam at 452 K | -236,647,000 |
2 |
1 |
0.485 |
| Steam at 531 K | -233,995,000 |
2 |
1 |
0.413 |
| Steam at 624 K | -230,872,000 |
2 |
1 |
0.351 |
| Hydrogen | -8,123,000 |
2 |
0 |
70.800 |
Propellant heat of formation is the amount of energy per kilomole of substance required to form the molecule in the state it is in while in the propellant tank from elemental molecules at standard conditions. A positive number means energy is required to form the molecule and it will release energy when going to the standard state of its elemental components. A negative number means energy is released when forming the molecule and it will absorb energy when going to the standard state of its elemental components. Generally the higher the number, the more reactive or volatile the substance will be. When a substance is heated, its heat of formation rises.
Water is the most commonly used propellant in large liquid fueled rockets, often in solution with hydrogen peroxide. The hotter the water, the higher its heat of formation and therefore the higher its exhaust velocity. Hydrogen in sometimes used in electrically heated engines. The propellant heat of formation is used to calculate the mix heat, which is in turn used to calculate the reactant enthalpy.
mix heat = oxidizer mix * oxidizer heat of formation + propellant mix * propellant heat of formation
reactant enthalpy = fuel molar ratio * fuel heat of formation + mixture oxidizer mix * mix heat
This is used in tripropellant rocket, pumped rocket and rocket cost.
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