[kevinnn]

    i was also just wondering why does hydrogen gas spontaneously ignite under normal conditions??? i noticed that the auto ignition temp was about 500F, i know for a fact that it is not 500F outside so why does it burn without an ignition source?? 

    the way that i am making hydrogen gas is by putting lithium metal in water, if i put a small piece in it will just make the gas and not set on fire, but, if i put a larger piece in it will set on fire and then end in a somewhat firework like display shooting little white fiery balls everywhere, or at the very least making a pop about as loud as a fire cracker seconds after ignition.  any help on understanding this would be great, thanx a lot

[opti384]

Well it is known that hydrogen reacts with almost every oxidizing element. Pure hydrogen itself might not ignite by itself but it's because hydrogen is mixed with oxygen (an oxidizer).

[vmelkon]

Portions of the lithium would produces very high temperature, probably well above 1000 °C so it can set the hydrogen on fire.

Why it blows up if you put lithium in it? I imagine it gets hot enough that the lithium melts and a lot of droplets and accelerate the reaction. I imagine that it is a combination of water as a gas and hydrogen combining with oxygen that causes the popping.

[rabolisk]

Hydrogen gas does not spontaneously ignite under normal conditions. You can definitely have hydrogen gas mixed with atmosphere without any combustion. However, producing H₂ gas by putting lithium metal in water acts as an ignition source, to my understanding.

Well it is known that hydrogen reacts with almost every oxidizing element. Pure hydrogen itself might not ignite by itself but it's because hydrogen is mixed with oxygen (an oxidizer).

By definition, ignition (combustion) requires an oxidant. With respect to auto-ignition temperature, this refers to combustion in normal atmosphere.

[vmelkon]

Hydrogen gas does not spontaneously ignite under normal conditions. You can definitely have hydrogen gas mixed with atmosphere without any combustion. However, producing H₂ gas by putting lithium metal in water acts as an ignition source, to my understanding.

Well it is known that hydrogen reacts with almost every oxidizing element. Pure hydrogen itself might not ignite by itself but it's because hydrogen is mixed with oxygen (an oxidizer).

By definition, ignition (combustion) requires an oxidant. With respect to auto-ignition temperature, this refers to combustion in normal atmosphere.

Yes, for sure. I have had hydrogen mixed with air and hydrogen mixed with pure oxygen. It requires an ignition source to burn.

To the OP, try it. It is easy to produce hydrogen. I have produced large quantities of hydrogen by electrolysis. You can also drop some zinc or magnesium in sulfuric acid.

[billnotgatez]

It takes only a slight spark to cause hydrogen to ignite (static release will do it)

from WIKI

Hydrogen gas (dihydrogen or molecular hydrogen) is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion for hydrogen is −286 kJ/mol

I have heard that 85 to 90% is more like it   5 to 85
but that might be a rule of thumb