If a mole of hydrogen reacts with a mole of oxygen to produce water, what is the excess reactant?

Oxygen is the excess reactant.

Explanation: A simple balanced chemical equation for the production of water, will show:

2H2 + O2 > 2H20

2 : 1 2

From this, we can see that 2 moles H2 react with 1 mole of O2 to produce 2 moles of H2O. That is to say, hydrogen reacts with oxygen in the ratio 2:1

Also if 1 mole of H2 is needed to produce water, it will require 1/2 mole of O2 to react with.

Since we know this, we can tell from our question that 1 mole of H2 will react with 1/2 mole of O2 and be left with 1/2 mole of O2 as excess.

We can have a chemical equation for this as:

1/2H2 + O1/2 > 1/2H2O

1 : 1/2

Therefore, the H2 can be said to be the limiting reactant (gets consumed when the reaction is completed) while the oxygen is the excess reactant.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.