What feature related to composition do all compounds with the same percent composition have? Provide your answer as a grammatically correct sentence.

Chemical composition is a fundamental concept in chemistry that describes the exact proportion of elements within a compound. Every molecule has a set formula which dictates its chemical nature and behavior. For example, water (H2O) always consists of two hydrogen atoms for every one oxygen atom, a 2:1 ratio. Understanding a substance's chemical composition is crucial because it determines the substance’s properties, reactivity, and applications.

Differences in chemical composition, even if seemingly minor, can lead to substances with very different characteristics. Take, for example, carbon dioxide (CO2) and carbon monoxide (CO). Although both compounds contain carbon and oxygen, their differing ratios result in remarkably distinct properties with carbon monoxide being a poisonous gas, while carbon dioxide is a non-toxic, naturally occurring gas crucial in the respiratory processes of plants.

The mass ratio of elements in a compound is a precise measure that shows the mass of one element relative to the mass of either another element in the compound or the entire compound itself. This ratio is particularly valuable when comparing different substances that might appear similar or when deducing the empirical formula of a compound from the masses of its constituent elements.

For instance, glucose (C6H12O6) and fructose (C6H12O6) have the same molecular formula, but they are distinct compounds with different structures and properties, a case of isomerism. However, because they have the same formula, they share the same mass ratio of carbon to hydrogen to oxygen, which is 6:12:6. This ratio helps chemists understand and predict the behavior of compounds during chemical reactions.

Stoichiometry is the quantitative relationship within a chemical equation used to calculate amounts of reactants and products. It is rooted in the conservation of mass and the concept of moles, allowing chemists to convert masses into moles to find ratios in a balanced chemical equation.

For example, in the process of photosynthesis, six molecules of carbon dioxide react with six molecules of water to produce one glucose molecule and six oxygen molecules. The stoichiometric coefficients in 6CO2 + 6H2O → C6H12O6 + 6O2 show the exact ratios needed for the reaction. These coefficients are vital for scientists because they need to know the precise amounts of substances required for chemical processes, whether to produce aspirin in a pharmaceutical lab or to calculate the oxygen needed for an astronaut's life support system in space.