[Sarah32]

One more question lol
I was reading that when you boost your car battery incorrectly it produces Hydrogen gas. Which of course is very back if a spark comes flying out but why is the spark needed for the explosion to occur?
I'm assuming hydrogen gas is extremely flammable, can someone put this into simple terms for me?
Thxs

[enahs]

You need some sort of activation energy to start the reaction between hydrogen and oxygen. Once that is achieved, the process is exothermic (produces heat) and can produce enough energy in the form of heat to continue the reaction.

[Yggdrasil]

Probably the amount of hydrogen produced is not enough to create a dangerous explosion or even to sustain a fire.

[lemonoman]

Thanks Yggdrasil.  I was just about ask for clarification because I didn't really get what enahs said lol

[enahs]

bah, non-sense. There can be plenty of hydrogen produced to create a dangerous explosion. I have seen one with my own eyes before! heh


And how could you not get what I said? The spark is the activation energy required to start the reaction, which is exothermic and can self sustain its self.

[lemonoman]

And how could you not get what I said? The spark is the activation energy required to start the reaction, which is exothermic and can self sustain its self.

Ohhh.  For some reason I didn't understand how your answer related to the question.  But after a couple beers, I get it

Badly-wired Battery --> Hydrogen
Hydrogen --> More hydrogen (exothermic reaction)
More hydrogen + Spark --> Kaboom
-----------------------------------
Badly-wired Battery + Spark = Kaboom

[AWK]

Hydrogen explodes in air (after ignition) at concentrations within 4 to +75 molar %

http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html

[IITian]

Taken from Journal of Catalysis 191, 282-293 (2000)

H₂(g) + 12O₂(g) -> H₂O(g) + 57.9 kcal

the explosion limits for H₂ in O₂ ranging from  4% to 94%, on a volume percent basis, and from 4% to 75% for H₂ in air, the safety issues cannot be overstressed and expensive equipment and reactors are normally required to handle the reaction.