Thread: Law of Definate Proportions?

I can not get my head around it.

It is one of the first things you learn in chemistry and it is a dead end for me.

Could someone explain it to me like I am a 8 year old with some good easy to understand examples.

Almost everyone knows that chemical formula for water is H2O. That means every molecule of water - that's every molecule of water - is made up of two hydrogen atoms and one oxygen atom. Now every oxygen atom in the universe has the same mass as every other one. (For simplicity I am going to pretend isotopes don't exist.) And so too, every hydrogen atom. So whether you are dealing with one molecule of water, or trillions of molecules of water, the ratios of the masses of hydrogen to oxygen will be the same in every case. That's the Law of Definite Proportions.

I learned it as the law of constant proportions. Is that the same thing?

I believe so.