Balanced Photosynthesis Equation

Balanced Photosynthesis Equation

Photosynthesis is one of the most important processes. It’s directly responsible for the air that we breathe! If you’re hoping to learn how to balance the photosynthesis equation, then read on!

What Is Photosynthesis?

Photosynthesis is the process that plants use to generate chemical energy, creating it from a complex chemical process that uses light to create fuel for the plant.

It’s from this process that the name is derived – photosynthesis referring to the creation of something from light.

It is one of, if not perhaps the single most important biological processes when we consider its effect on the earth.

This is because photosynthesis releases oxygen as a waste product – meaning that photosynthesis in algae and plants is directly responsible for the oxygen content in the air that we breathe.

The vast majority of plants and algae produce energy using photosynthesis – and, of course, by extension produce oxygen that we breathe.

There are even bacteria that use photosynthesis, called cyanobacteria.

In fact, it is thought that some of the most important organisms to use photosynthesis are cyanobacteria, long before the evolution of far more complex organisms such as plants and trees.

Cyanobacteria contributed directly to the oxygenation of planet Earth, which in turn made all complex life as we know it possible.

And, of course, due to the fact that photosynthesis still produces the oxygen that humans and animals use, it’s responsible for creating the air that we and the creatures around us breathe to live every day.

Balanced Photosynthesis Equation Part 1

The simplified, unbalanced equation for photosynthesis is as follows:

Carbon Dioxide + Water → Glucose + Oxygen

This can be written out as follows:

CO2 + H2O → C6H12O6 + O2

However, there are a few problems with this equation if left like this. Firstly, it omits an important part of the photosynthesis process – namely, light.

Energy from light is required for photosynthesis to occur at all. So, a better way to write the equation out is like this:

CO2 + H2O + Light energy → C6H12O6 + O2

This is better, as it accounts for the light energy that is necessary for the process of photosynthesis. However, the equation is unbalanced.

Looking at the glucose molecule on the right hand side of the equation, we can see that there are far more hydrogen and carbon molecules than are provided by the carbon dioxide and water molecules on the left hand side.

These extra molecules can’t simply appear out of nowhere. Therefore, for the equation to make any sense, we have to balance it.

The first step is to look at the amount of atoms of each element that there are in the glucose molecule on the right hand side of the equation.

After all, there are more atoms here than in any other molecule in the equation. We can see straight away that there are 6 carbon atoms in the molecule.

Yet, the carbon dioxide molecule on the left hand side has only one carbon atom.

Therefore, in order to begin balancing the equation, we should start with the carbon dioxide molecule.

Clearly, in order for this equation to be balanced, we need to have 6 carbon atoms – which means that we need to have 6 carbon dioxide molecules, in order to have enough carbon for the glucose.

This means we should write the equation like this now:

6 CO2 + H2O + Light energy → C6H12O6 + O2

Things are starting to look a little more balanced now, but we’re not quite there yet. Looking back again at the glucose molecule on the right hand side of the equation, we see that there are 12 hydrogen atoms.

Looking at the left hand side, we see that hydrogen is only provided in this equation by the water molecule. There are two hydrogen atoms for each molecule of water, but glucose needs 12.

Therefore, we can clearly see that we need more water molecules to balance this equation too!

As each water molecule has 2 hydrogen atoms, we can work out that to get 12 hydrogen atoms, we’ll need 6 water molecules. So, the equation now looks like this:

6 CO2 + 6 H2O + Light energy → C6H12O6 + O2

Balanced Photosynthesis Equation Part 2

The equation is now much closer to being balanced, but we’re not quite there yet! We have 6 carbon atoms, and 12 hydrogen atoms all accounted for.

However, with the increased number of molecules on the right side, we now have a lot of oxygen atoms to account for.

The glucose molecule has 6 atoms of oxygen.

In the original equation, we had one molecule of water and one molecule of carbon dioxide, which gave us a total of three atoms of oxygen.

However, now that we have 6 molecules each of carbon dioxide and hydrogen, we have 12 atoms of oxygen coming from carbon dioxide, and a further 6 coming from water.

This gives us a total of 18 oxygen atoms.

On the right hand side of the equation the glucose molecule contains 6 oxygen atoms, and the oxygen molecule contains two.

As we have 10 atoms of oxygen left over, to balance the equation we can see that with 6 molecules of carbon dioxide and 6 molecules of water we should write the equation like this:

6 CO2 + 6 H2O + Light energy → C6H12O6 + 6 O2


We can now see that the 6 molecules of water and 6 molecules of carbon dioxide combine with light energy to give one molecule of glucose and six molecules of O2.

Therefore, the equation is now balanced!

Jennifer Dawkins