Sciencemadness Discussion Board - water chem

water chem

liljoe086 - 28-5-2007 at 07:34

HI, new here but I thought it best to just dive right in.

We all know the combusion of H and O we get water
My question is, is this reaction possible

2H- + O + (activation energy) => H2O + heat

can you use hydrogen ions to make water.

Nerro - 28-5-2007 at 07:41

Chemistry doesn't get much more basic than this...

First off, you have the reaction wrong it goes as follows:
2H2 + O2 -> 2H2O

And second, hydride ions will not exist freely and as such they won't react with oxygen to form water. More over, where would the charge go? You have 2- on the left and no charge on the right! You can't just turn electrons into heat like that it doesn't work that way.

liljoe086 - 28-5-2007 at 08:01

Quote:

Originally posted by Nerro
Chemistry doesn't get much more basic than this...

First off, you have the reaction wrong it goes as follows:
2H2 + O2 -> 2H2O

And second, hydride ions will not exist freely and as such they won't react with oxygen to form water. More over, where would the charge go? You have 2- on the left and no charge on the right! You can't just turn electrons into heat like that it doesn't work that way.

Opps sorry about the equation, im not sure how to make a subscript

so i left it in a single form but yes you need the diatomics.
OK then take me back to the basics. What actually occurs in the basic equation. The 2 atoms want to go to a lower energy state, but requires a push for the reaction to happen (activation energy). When the right amount is added, the reaction can happen. Normal H has 1 e- and O has 8. Tell me what occurs.

12AX7 - 28-5-2007 at 08:26

The molecules have to be broken. A small amount of molecules posess a large amount of energy (read up on thermal statistics for why), and the number increases with temperature. Above a few electron-volts, molecules dissociate and produce radicals: O2 <--> 2O. Oxygen atoms are very reactive. One might steal electrons from a nearby hydrogen molecule as O + H2 = H2O, thereby leaving another oxygen free to do the same. Photodissociation can cause the same thing without heat. In this case, you'd want light in the 200nm range (UV-C), which carries enough energy to break oxygen atoms.

The resulting water molecule carries a lot of energy and may dissociate: H2O <--> H + OH. Hydroxyl radicals are nasty oxidizers; this reaction allows contaminants to be cleared from the atmosphere (hydroxyls react with methane, carbon monoxide, hydrocarbons, etc. to give H2O and CO2, etc.), albeit slowly. The molecule's energy may also smack into other molecules, breaking off another oxygen atom, say. There are many possible reactions, but this is the jist of it.

If few of these radicals are present, the reaction proceeds very slowly. If a critical number of them exist at any point, the reaction snowballs and the mixture is able to explode by a cascade of these reactions.

Note that I have done nothing with electrons. Nature tends to make charge-neutral species. H2O <--> H+ + OH- proceeds to some extent (namely, 10^-14) in liquid water, but radicals are preferred at high temperature. It's more useful to think in terms of atoms and their reactivity (which is due to unpaired electrons) than the number of electrons. The number of electrons goes more into predicting molecular nature (Lewis dot structures and VSEPR theory for example).

Tim

YT2095 - 28-5-2007 at 08:31

sounds almost like a Fuel Cell.

liljoe086 - 28-5-2007 at 08:41

Quote:

Originally posted by 12AX7
The molecules have to be broken. A small amount of molecules posess a large amount of energy (read up on thermal statistics for why), and the number increases with temperature. Above a few electron-volts, molecules dissociate and produce radicals: O2 <--> 2O. Oxygen atoms are very reactive. One might steal electrons from a nearby hydrogen molecule as O + H2 = H2O, thereby leaving another oxygen free to do the same. Photodissociation can cause the same thing without heat. In this case, you'd want light in the 200nm range (UV-C), which carries enough energy to break oxygen atoms.

The resulting water molecule carries a lot of energy and may dissociate: H2O <--> H + OH. Hydroxyl radicals are nasty oxidizers; this reaction allows contaminants to be cleared from the atmosphere (hydroxyls react with methane, carbon monoxide, hydrocarbons, etc. to give H2O and CO2, etc.), albeit slowly. The molecule's energy may also smack into other molecules, breaking off another oxygen atom, say. There are many possible reactions, but this is the jist of it.

If few of these radicals are present, the reaction proceeds very slowly. If a critical number of them exist at any point, the reaction snowballs and the mixture is able to explode by a cascade of these reactions.

Note that I have done nothing with electrons. Nature tends to make charge-neutral species. H2O <--> H+ + OH- proceeds to some extent (namely, 10^-14) in liquid water, but radicals are preferred at high temperature. It's more useful to think in terms of atoms and their reactivity (which is due to unpaired electrons) than the number of electrons. The number of electrons goes more into predicting molecular nature (Lewis dot structures and VSEPR theory for example).

Tim

Ok how does that help me

. As an aside I also believe the same range of UV-C is need to photodissociate H

Nerro - 28-5-2007 at 08:58

Oxygen on its own has 8 electrons, 2 s electrons in the first "shell", two s electrons in the second shell and 4 p electrons in the second shell. Chemists denote this electron-configuration as 1s22s22p4. Now oxygen is in it's lowest energy state when it has the same configuration as the first noble gas that comes after it on the periodic table. This is Neon which has two protons and two electrons more than oxygen which means it has the following electron configuration 1s22s22p6 (which is commonly denoted as [Ne]).

Hydrogen has 1 electron which means its electron configuration is simply 1s1, the next noble gas on the list is He which has two electrons so its electron configuration is 1s2.

This means that oxygen lacks two electrons and that hydrogen lacks one electron.

So when two hydrogen particles share their electrons with an oxygen particle they can all say they have enough electrons, the hydrogen particles will form a two-electron bond with the oxygen particle which means they will have two electrons in their outer shell which makes them a little like He and the oxygen particle has 2 extra electrons from the hydrogen which makes it a little like Ne. Now there are still as many electrons as there are protons but all particles have electron configurations that resemble that of the closest noble gas.

I'm not really going into it too much right now, does this make sense to you? If it does not just draw the lewis structure for water and you will see that the hydrogen's each have two electrons in their outer shell and that the oxygen has 8 electrons in it's outer shell.

liljoe086 - 28-5-2007 at 09:11

Quote:

Originally posted by Nerro
Oxygen on its own has 8 electrons, 2 s electrons in the first "shell", two s electrons in the second shell and 4 p electrons in the second shell. Chemists denote this electron-configuration as 1s22s22p4. Now oxygen is in it's lowest energy state when it has the same configuration as the first noble gas that comes after it on the periodic table. This is Neon which has two protons and two electrons more than oxygen which means it has the following electron configuration 1s22s22p6 (which is commonly denoted as [Ne]).

Hydrogen has 1 electron which means its electron configuration is simply 1s1, the next noble gas on the list is He which has two electrons so its electron configuration is 1s2.

This means that oxygen lacks two electrons and that hydrogen lacks one electron.

So when two hydrogen particles share their electrons with an oxygen particle they can all say they have enough electrons, the hydrogen particles will form a two-electron bond with the oxygen particle which means they will have two electrons in their outer shell which makes them a little like He and the oxygen particle has 2 extra electrons from the hydrogen which makes it a little like Ne. Now there are still as many electrons as there are protons but all particles have electron configurations that resemble that of the closest noble gas.

I'm not really going into it too much right now, does this make sense to you? If it does not just draw the lewis structure for water and you will see that the hydrogen's each have two electrons in their outer shell and that the oxygen has 8 electrons in it's outer shell.

Actually that is what is was looking for ty

12AX7 - 28-5-2007 at 10:58

Quote:

Originally posted by liljoe086
Ok how does that help me

. As an aside I also believe the same range of UV-C is need to photodissociate H

Well, you didn't say what it is you want to know about. It sounded like combustion (which is a free radical process). It turns out you wanted to know about covalent bonding...

Tim