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Reactants to Products
A chemical equation is like a recipe for a reaction so it displays all the ingredients or terms of a chemical reaction. It includes the elements, molecules, or ions in the reactants and in the products as well as their states, and the proportion for how much of each particle is create relative to one another, through the stoichiometric coefficient. The following equation demonstrates the typical format of a chemical equation:

[2 Na_{(s)} + 2HCl_{(aq)} \rightarrow 2NaCl_{(aq)} + H_{2\;(g)} \tag{1}]

In the above equation, the elements present in the reaction are represented by their chemical symbols. Based on the Law of Conservation of Mass, which states that matter is neither created nor destroyed in a chemical reaction, every chemical reaction has the same elements in its reactants and products, though the elements they are paired up with often change in a reaction. In this reaction, sodium ((Na)), hydrogen ((H)), and chloride ((Cl)) are the elements present in both reactants, so based on the law of conservation of mass, they are also present on the product side of the equations. Displaying each element is important when using the chemical equation to convert between elements.

Stoichiometric Coefficients
In a balanced reaction, both sides of the equation have the same number of elements. The stoichiometric coefficient is the number written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation. Though the stoichiometric coefficients can be fractions, whole numbers are frequently used and often preferred. This stoichiometric coefficients are useful since they establish the mole ratio between reactants and products. In the balanced equation:

[2 Na {(s)} + 2HCl{(aq)} \rightarrow 2NaCl_{(aq)} + H_{2(g)} \tag{2}]

we can determine that 2 moles of (HCl) will react with 2 moles of (Na_{(s)}) to form 2 moles of (NaCl_{(aq)}) and 1 mole of (H_{2(g)}). If we know how many moles of (Na) we start out with, we can use the ratio of 2 moles of (NaCl) to 2 moles of Na to determine how many moles of (NaCl) were produced or we can use the ration of 1 mole of (H_2) to 2 moles of (Na) to convert to (NaCl). This is known as the coefficient factor. The balanced equation makes it possible to convert information about one reactant or product to quantitative data about another element. Understanding this is essential to solving stoichiometric problems.