Understanding the Chemical Formula for Photosynthesis

Photosynthesis is the process by which green plants and some other organisms utilize sunlight to synthesize foods with the help of carbon dioxide and water. The general chemical equation for photosynthesis is:

6CO2 6H2O sunlight chlorophyll → C6H12O6 6O2

Key Concepts in Photosynthesis

To understand the chemical formula for photosynthesis, it is essential to grasp the fundamental concepts of stoichiometry. Stoichiometry deals with the determination of the combining proportions or chemical equivalents of the reactants and products involved in a chemical reaction.

The Importance of Proportions in a Reaction

The proportion of each element or compound is crucial in a reaction. For example, in the photosynthesis reaction, six molecules of carbon dioxide (CO2) and six molecules of water (H2O) are required to produce one molecule of hexose sugar (C6H12O6) and six molecules of oxygen (O2).

Stoichiometry of Photosynthesis

For the fixation of six molecules of CO2 into one molecule of hexose sugar, the process requires 12 NADPH and 18 ATP to complete two cycles of the Calvin cycle. The reduction of CO2 is driven by hydrogen atoms, and the source of hydrogen is only water (H2O). During photosynthesis, CO2 is reduced into a carbohydrate, and the hydrogen comes from H2O.

Therefore, to start with, we must write CO2 in the equation, as both CO2 and H2O are reactants. The given equation in the query is unbalanced, and both sides of the reaction must have an equal number of atoms.

Balancing the Chemical Equation

The reason for writing 12 H2O is because 12 NADPH2 are required to reduce 6 molecules of CO2 and to release 6 molecules of O2. 12 OH only yields 6H2O 6O2. In the query, in the reactant side, 7 H2O gives only 6 NADPH2, which can reduce only 3 molecules of CO2. The required number is 12 NADPH2.

Moreover, O2 is released only from the water, not from CO2. So, in order to produce 6 molecules of O2, 12 H2O are required. Thus, to meet the requirement of NADPH2, we need 12 NADPH2 for which we need 12 H2O to complete the reaction to produce 1 molecule of glucose (C6H12O6). The empirical formulae of 18 ATPs and 12 NADPH2 through the Calvin cycle indicate that the cycle has to repeat twice.

Without the required number of sources of each element in the reactant side, the reaction cannot reach the products.

The Chemical Reaction for Photosynthesis

Though I am not going to attempt to write the structural formula of glucose, we know that photosynthesis accomplishes the fixation and reduction of atmospheric carbon dioxide and water to give simple sugars with dioxygen as the oxidation product:

6CO2(g) 6H2O(l) sunlight chlorophyll → C6H12O6(aq) 6O2(g)

This reaction is endothermic, meaning it requires energy input, specifically from sunlight, to proceed.

Endothermic Reaction

Per the laws of thermodynamics, an endothermic reaction absorbs heat from its surroundings. Photosynthesis is an energy-dependent process that requires energy from sunlight to drive the reactions that convert carbon dioxide and water into glucose and oxygen.