How can we say that water contains hydrogen and show the reaction too.
Hydrogen + Oxygen = Water The simple statement that water is made from hydrogen and oxygen doesn't give us a very clear picture of what really goes into the creation of a molecule of water. A quick look at the chemical equation for the formation of water tells us more.
2H2 + O2 = 2H2O
It takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2. There's something more though that doesn't show up in the equation.Energy. The formation of water from it's elements produces, in addition to water, a tremendous amount of energy, 572 kJ to be exact.
2H2 + O2 = 2H2O + ENERGY
This is an example of an exothermic reaction, a reaction that produces energy.