Can You Burn Water?

If you are not the greatest at cooking, or have spent enough time on social media to come across others who have seemingly “burnt water” in an attempt to cook, you might have had the question “Can you actually burn water?”

While the images seem like a convincing burn with black residue and smoke, the actual process of “burning” works slightly differently, especially in the case of water.

So no, no matter how bad you are at cooking, you can not burn water, and here is why:

The main reason water can not be burned is because water itself is a result of burning.

We are all familiar with the equation of water with hydrogen and oxygen:

2H2​+O2​→2H2​O

This is an example of a combustion or burning reaction. The typical characteristics of a combustion reaction is that it is exothermic, meaning energy is released along with the products.
We can prove that the combustion of hydrogen and oxygen to create water is exothermic through the following equation:
Net energy change = (Energy absorbed) - (Energy released)
If the net energy change has a positive sign, it means that the reaction is endothermic and energy is absorbed.
However, if it has a negative sign, the energy is exothermic and energy is released.

Let's break this equation down into two parts and observe how it goes in the case of water:
Energy absorbed: Energy absorbed means the amount of energy required to break the bonds between the oxygen molecules and hydrogen molecules. This energy is often also referred to as “bond energies”.
The bond energies between the hydrogen molecules and oxygen molecules that undergo combustion are:
H-H bond: ≈ 436 kJ/mol
O=O bond: ≈ 498 kJ/mol
In the reaction in Figure 1, there are two molecules of hydrogen and one molecule of oxygen.
Therefore the total energy absorbed in the combustion is:
2 H-H bonds (2 * 436 kJ) + 1 O=O bond (1 * 498 kJ) = 872 + 498 = 1370 kJ/mol

Energy released: Forming new bonds releases energy as heat and light. As a result of the combustion reaction, 2 molecules of water and 4 O-H bonds are formed.
The energy released when an O-H bond is formed in water is approximately 463 kJ/mol
When we multiply this by 4 we get:
4 * 463 kJ/mol = 1852 kJ/mol

When we put these values in the equation
Net energy change = (Energy absorbed) - (Energy released)
Net energy change = (1370 kJ/mol) - (1852 kJ/mol)
= -482

We have mentioned earlier that if the sign of the net energy change is negative, it means that the reaction is exothermic. However, what does that have to do with burning water?
For a burning or combustion reaction, we need three things: a fuel to be burned, oxygen to burn, and heat to start the reaction.

The definition of fuel, in terms of chemistry, is a compound that has stored energy.
When oxygen molecules and hydrogen molecules undergo combustion, all the energy stored within the bonds have been released. and there is no more energy left for water to undergo combustion.
Thus, water can not be counted as a fuel, and can not be burned.