Hydrogen and Oxygen burn

  • Thread starter Curl
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  • #1
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Main Question or Discussion Point

Hydrogen and Oxygen "burn"

Does anyone know the temperature at which this reaction becomes spontaneous?

2H2O--> 2H2 + O2

I can't find my book with thermodynamic data, but it should be cake for you guys.

Thanks.
 

Answers and Replies

  • #2
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Does anyone know the temperature at which this reaction becomes spontaneous?

2H2O--> 2H2 + O2

I can't find my book with thermodynamic data, but it should be cake for you guys.

Thanks.
What is the definition of spontaneity?
 
  • #3
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The auto-ignition temperature of hydrogen in air at STP is roughly 530'C depending on concentration and what not.

What is the definition of spontaneity?
I think he just means at what temperature will a self-sustaining redox reaction occur.
 
  • #4
alxm
Science Advisor
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The definition of a 'spontaneous reaction' is deltaG < 0, although I think sjb-2812 might've been asking that rhetorically.

The number I get for that is about 1750 K.
 
  • #5
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Thanks alxm.

I'm assuming you did this for 1atm pressure right? And how did you get the Gibbs values for the substances at those temperatures? Is it accurate to assume a linear relationship between G and temperature? Most tables I've seen offer values for 25C or so.

Also, what keeps the reverse reaction from happening at temperatures lower than this? I've seen H2 and O2 in a balloon and it didn't spontaneously react into water until a flame was brought up. What happens there? I haven't studied kinetics much, all I know is from stat mech.
 

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