Because it is a fast reactant and works and warns up within the 15 mins.
Not to waste time.
The francium hydride should be FrH.
Because then there would be no reaction.
frh
Maybe because the chemicals might be ruined or not considered "chemicals" anymore. As you all know, water purifies things; it doesn't destroy things. Chemicals are in the FRH. Water would purify it.
The airport code for French Lick Municipal Airport is FRH.
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There are small pieces of magnesium in Flameless Ration Heaters (FRH). They are typically in the form of a thin strip or coil that reacts with water to produce heat for heating up food items.
For conventional flow (plus to minus) FLH rule is for motor action, and FRH rule is for generator action. So you can use FRH rule to determine the direction in which voltages are induced into the rotor by the rotating magnetic field, then use FLH rule to determine the direction in which the resulting forces, due to the rotor-bar currents, will act to rotate the rotor.
Because adding water to it activates it. It would be pointless to pack a previously activated ration heater in MREs. That, and the one thing service members can pretty well count on, even in combat situations is water for their canteen or Camel Back hydration system. Additionally, the MRE pouch is a tough, sealed, plastic bag, not easily opened without a knife. The FRH is essentially a battery when water is added (see the chemical reaction between magnesium and iron powder, salt, and water). One of the byproducts of activation of the FRH is hydrogen gas, which anyone who has seen the video footage of the Hindenburg Disaster knows is extremely volatile. Imagine the service member sitting on a rock in the field, preparing to enjoy his nutritious Meal, Ready-to-eat, puffing away on his Lucky Strike, when he drives his M7 bayonet into the bloated pouch containing his FRH with the water conveniently added by the manufacturer. Now imagine the expression on the faces of the group of insurgents a klick or so away when they hear a sharp crack, look up to see a small white mushroom cloud over the next hill, and get a whiff of burnt GI crewcut. That, kids, is why the flameless reaction heater doesn't come with water already inside.
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When francium and hydrogen combine, they form francium hydride (FrH), a compound where francium acts as a cation and hydrogen as an anion. Francium is extremely rare and radioactive, making it difficult to study its chemical properties in detail. The compound would likely be highly unstable due to francium's extreme reactivity.