The key difference between composition and reaction stoichiometry is that composition stoichiometry refers to the atomic make-up of a chemical compound, whereas reaction stoichiometry refers to the amount of compounds consumed or produced during a chemical reaction.
Stoichiometry is a chemical term that describes the quantitative data about a chemical compound or a chemical reaction. If this data is about a chemical compound, then we call it composition stoichiometry; if it is about a chemical reaction, we can call it reaction stoichiometry.
CONTENTS
1. Overview and Key Difference
2. What is Composition Stoichiometry
3. What is Reaction Stoichiometry
4. Side by Side Comparison – Composition vs Reaction Stoichiometry in Tabular Form
5. Summary
What is Composition Stoichiometry?
Composition stoichiometry is the quantitative analysis of a chemical compound regarding its atomic composition. This term refers to the types of atoms and their number present in a particular chemical compound. We can determine this using the chemical formula of the compound. Atomicity of a molecule gives the total number of atoms present in a chemical compound. But it does not give any detail about the chemical elements to which the atoms of the compound belong and their numbers. Nevertheless, we can use the composition stoichiometry of a particular compound to predict the chemical formula. Therefore, composition stoichiometry is simply the chemical make-up of a chemical species.
For example, composition stoichiometry of glucose molecule is given as six atoms of carbon, twelve atoms of hydrogen and six atoms of oxygen. Therefore, we can determine that one molecule of glucose contains carbon, hydrogen and oxygen atoms in the ratio of 6:12:6. This is the composition stoichiometry of glucose.
Figure 01: Chemical Composition of a Glucose Molecule
There are different ways to determine the composition stoichiometry of an unknown compound. Samples of the unknown compound can be used to determine the types of chemical elements in that sample along with the mass of each element. Then the number of moles of each element per sample can be calculated using these masses. The molar values can be rounded off to get the most possible ratio between the different types of atoms in the sample to predict the molecular formula.
What is Reaction Stoichiometry?
Reaction stoichiometry is the ratio between reactants and products of a certain chemical reaction. This phenomenon is very important in balancing a chemical reaction to get the relationship between reactants and how much product we can get from reacting those species.
Figure 02: An Example for a Reaction Stoichiometry
The concept of reaction stoichiometry is based on the law of mass conservation, which indicates that the total mass of reactants should be equal to the total mass of products because mass cannot be created or destroyed, can be only converted into other forms, just like energy.
Let us consider an example to understand the theory behind reaction stoichiometry. The reaction between an alkali metal and water produces heat energy, hydroxide of the metal, and hydrogen gas. Here, the details we know are the mass of alkali metal used and amount of water used for the reaction. After the completion of the reaction, the amount of hydrogen gas can be collected and using its volume, the moles of hydrogen gas evolved can be calculated. Therefore, assuming that all the alkali metal reacted with water, we can get the ratio between reactants and products involved in this reaction. This is the reaction stoichiometry of alkali metal in water reaction.
What is the Difference Between Composition and Reaction Stoichiometry?
The key difference between composition and reaction stoichiometry is that the composition stoichiometry refers to the atomic make-up of a chemical compound, whereas reaction stoichiometry refers to the amount of compounds consumed or produced during a chemical reaction. While composition stoichiometry gives the ratio between atoms of each chemical element present in a compound, reaction stoichiometry gives the ratio between reactants and products involved in a particular reaction.
Below infographic summarizes the difference between composition and reaction stoichiometry.
Summary – Composition vs Reaction Stoichiometry
Stoichiometry is a method of quantitative analysis of a chemical compound or a chemical reaction. The key difference between composition and reaction stoichiometry is that the composition stoichiometry refers to the atomic make-up of a chemical compound, whereas reaction stoichiometry refers to the amount of compounds consumed or produced during a chemical reaction.
Reference:
1. “Stoichiometry and Balancing Reactions.” Chemistry LibreTexts, Libretexts, 25 Sept. 2019, Available here.
Image Courtesy:
1. “Beta-D-Glucopyranose” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Combustion reaction of methane” By JyntoRobert A. RohdeJacek FHJynto – (Public Domain) via Commons Wikimedia