Question

Why we can’t make water by adding 2 molecules of hydrogen and a molecule of oxygen?

Answer 1

It is possible, a simple experiment that my chemistry professor once conducted had us putting hydrogen gas into a test tube, lighting a match and igniting the small amouny of gas in the tube. The end result was a small amount of water condensation at the bottom of the tube. Basically you can create a molecule given the presence of the right types of atoms, but a small amount of energy is required to create this reaction. Also the process is rarely ever that efficient, meaning you may need more than just the 2 and 1 atoms if you wish to increase your chances of success!