Hydrogen gas is an inflammable gas and oxygen plays a vital role in combustion process then how does water (hydrogen + oxygen) extinguishes it?
Water doesn't catch fire because it can't burn anymore. Burning in our atmosphere is a reaction with oxygen, and when we burn hydrogen in presence of oxygen in proper proportion by use of electric spark then the result is water. So the hydrogen has already been burnt. You can't burn twice.
The properties of a compound (like water) do not have any relation to the properties of the elements which it comprises.
In case of H2 the potential energy of H atom is more so it is less stable but when it combine with oxygen to form a molecule of water then its potential energy is minimum and it is more stable.
Now the hydrogen atoms in a water molecule are already in a stable state, and do not posess the potential energy of H atoms attached to each other. They do not explode(burn) on contact with oxygen because they don't have energy to give off.
A good analogy is to imagine 2 rocks of exactly equal properties; one at the top of a hill and one at the bottom. You nudge the one at the top of the hill and notice it rolls away down the hill. You walk down and nudge the other rock and notice it doesn't roll away. Why not? It's already at the bottom!
The reason water extinguishes flames is because it is exceptionally good at absorbing heat. Water both takes a lot of energy to raise in temperature and to transform into steam, so dumping a large quantity of water on a fire will decrease the temperature down to a level where flames are not actively propagating.
Source:-
https://www.quora.com/Why-does-water-not-catch-fire-but-instead-extinguishes-it-What-is-the-scientific-reason
Water doesn't catch fire because it can't burn anymore. Burning in our atmosphere is a reaction with oxygen, and when we burn hydrogen in presence of oxygen in proper proportion by use of electric spark then the result is water. So the hydrogen has already been burnt. You can't burn twice.
The properties of a compound (like water) do not have any relation to the properties of the elements which it comprises.
In case of H2 the potential energy of H atom is more so it is less stable but when it combine with oxygen to form a molecule of water then its potential energy is minimum and it is more stable.
Now the hydrogen atoms in a water molecule are already in a stable state, and do not posess the potential energy of H atoms attached to each other. They do not explode(burn) on contact with oxygen because they don't have energy to give off.
A good analogy is to imagine 2 rocks of exactly equal properties; one at the top of a hill and one at the bottom. You nudge the one at the top of the hill and notice it rolls away down the hill. You walk down and nudge the other rock and notice it doesn't roll away. Why not? It's already at the bottom!
The reason water extinguishes flames is because it is exceptionally good at absorbing heat. Water both takes a lot of energy to raise in temperature and to transform into steam, so dumping a large quantity of water on a fire will decrease the temperature down to a level where flames are not actively propagating.
Source:-
https://www.quora.com/Why-does-water-not-catch-fire-but-instead-extinguishes-it-What-is-the-scientific-reason
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