Question

When we perform electrolysis of water, we get hydrogen and oxygen evolved.

What are the conditions under which hydrogen and oxygen combine to form water?? ​

Answer 1

Electrolysis

By the process of electrolysis we can break water molecule into hydrogen and oxygen but in order to form water, this method may not work.

Why?

Decomposition of water is entirely different than forming water. Water which is basic need can't be formed as easily as breaking water into it's reactants.

How?

Though formation of water by reaction is known to us from many years but while reacting Hydrogen with Oxygen specially using 2 molecules of Hydrogen is termed as Oxygen Reduction Reaction but not Hydrogen Oxidation Reaction.

Conditions

• A special catalyst is used to have specifically reaction of 2 molecules of Hydrogen with 1 molecule of oxygen.
• A required pressure has to be maintained to have reaction.
• A required amount of heat has to be provided where hydrogen can react with oxygen.

Out of so much efforts, a nominal amount of water is obtained

Answer 2

Answer:-

$\large{\rm{\underline{Electrolysis\:of\:Water:-}}}$

If direct current (D.C.) is passed through acidified water (H2O) , two gases are evolved. At the positive electrode (anode) oxygen is liberated , whereas at the negative electrode (cathode) hydrogen is set free. The change can be represented as follows :-

$\bold{\sf{Water \: \rightarrow \: Hydrogen \:+ \:Oxygen}}$

The product formed on electrolysis , i.e. , hydrogen and oxygen are new substances as they are chemically different from water (H2O) from which they are formed .

The change involves absorption of energy in the form of electricity. The change is permanent as water cannot be obtained simply by mixing hydrogen and oxygen. Thus , the electrolysis of water is a chemical change.

$\bold{\rm{\underline{Conditions\:required\:to\:form\:water:-}}}$

Special conditions are needed to form water by combining hydrogen and oxygen :-

$\bold{\rm{\underline{Presence\:of\:catalyst:-}}}$

Catalyst is that substance which increases the rate of chemical change and remains unchanged in amount and chemical composition at the end of the change . When we simply mix oxygen and hydrogen, nothing happens. But when we add a amount of heat by spark or a matchstick, the reaction starts activating.

$\bold{\rm{\underline{Temperature:-}}}$

Water is not formed at normal or room temperature . Producing water from hydrogen and oxygen usually requires a high temperature. A minimum temperature of 536°C must be maintained.

Note:-

After reading the above points, a question comes to our mind that why don't we overcome the problem of water by combining hydrogen and oxygen simply . The answer to this question is that combining hydrogen with oxygen is a combustion reaction and we know very well that in a combustion reaction , energy is released. When we combine hydrogen and oxygen under favourable conditions, then the bonds between hydrogen and oxygen changes which releases a very high amount of energy. That's why we only use this technique to form water in laboratories in a small amount.

If we will try to practise this at a large extent, it would result into a BOOM.