Hydrogen fuel cells
Energy from hydrogen does not make greenhouse gasses, so if storage of liquid hydrogen is possible, it can be used as a clean fuel. However, storage of hydrogen as a compressed gas or cooled to a liquid takes energy.
Rockets
Show a dramatic video of a real rocket taking off e.g. Artemis II for Moon flyby in 2026: https://www.youtube.com/watch?v=PGBoVotHqIE
The core stage rocket in the centre is a hydrogen-fueled rocket, acting after he solid rocket boosters separate at about 2 minutes.
Discuss how real rockets work:
The "rocket fuel" is mixed with an "oxidizer" in the combustion chamber. They chemically react and make new molecules, including a gas. The huge amount of gas produced (called "exhaust") can only escape out of a nozzle built into the back of the rocket. The action of the exhaust shooting out exerts an equal and opposite force on the rocket, which propels the rocket upwards. (Newton's Third Law of Motion: Action and Reaction).
(If the baking soda/vinegar rocket activity or Alka seltzer activity has been done, remind students that it is the same mechanism.)
Model the chemical reaction in fuel cells or LOX/LH2 rockets
Give the students their molecule pieces.
O2 (liquid oxygen or 'LOX' in rockets) + 2 H2 (liquid hydrogen or 'LH2' in rockets).
(In a rocket engine, they are stored at very low temperatures, so are liquid.)
Tell them that in the fuel and oxidant are mixed, and the oxygen and hydrogen chemically react to make a new molecule. Ask them to take apart their oxygen and hydrogens and rebuild two identical molecules.
They should make two water molecules, 2 H2O. They might recognize this molecule when it is called by it's chemical formula.
In a fuel cell the chemical reaction makes heat, water (mostly gaseous) and electricity.
In the rocket the chemical reaction makes heat and gaseous water, which escapes through the nozzle and gives the rocket thrust.
Other facts about rocket fuels:
The fuel is a significant portion of the rocket mass, so as the fuel is burned up, the rocket gets significantly lighter and accelerates upwards.
The boosters (on the side) run out of fuel first, then the main engine.
The propellants of a rocket are often a "fuel" and a source of oxygen "an oxidizer".
The most efficient fuel and oxidizer combination is liquid oxygen (the oxidizer, also called LOX) and liquid hydrogen (the fuel, also called LH2), as we modelled here.
Liquid oxygen ("LOX") is the oxidizer commonly used in rockets.
Other fuels used besides liquid hydrogen are kerosene or methane.
Chemical reaction for kerosene: 2 C12H26(l) + 37 O2(g) → 24 CO2(g) + 26 H2O(g)
Chemical reaction for methane: CH4 + 2O2 → CO2 + 2H2O
A rocket where the fuel or oxidizer (or both) are gases liquefied and stored at very low temperatures (below −150 °C) is called a cryogenic rocket engine. If the propellants had been stored as pressurized gases, the size and mass of fuel tanks themselves would severely decrease rocket efficiency.
Rockets have to carry their own oxygen into space, where there is no air.
This is in contrast to aeroplanes, which use atmospheric oxygen to oxidize their fuel.
"Monopropellants" are just one molecule (e.g. hydrogen peroxide or hydrazine) that can split into gas molecules, with a catalyst to speed up the reaction. Hydrogen peroxide decomposes into oxygen and water gases. Hydrazine decomposes into nitrogen and hydrogen gases. The gases produced are directed through a nozzle to create thrust.
First liquid-fuelled rocket in was launched in 1926. It flew 12metres. First satellite, Sputnik, launched in 1957 by the Soviet Union. 1961 was the first person in space.
