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Chemical reactions are fundamental processes where reactants transform into products. Imagine you’re in a dance, and dancers switch partners; that’s similar to how atoms in reactants rearrange to form new compounds. For this transformation to be complete, the reaction must be balanced, meaning the same number of each type of atom must exist on both sides of the equation.

Understanding chemical reactions involves recognizing reactant and product molecules, predicting the possible outcome of the reaction, and then confirming if energy is absorbed or released. For instance, when hydrogen gas ( (H_2)) reacts with bromine gas ( (Br_2)), they form hydrogen bromide ( (HBr)). This is a synthesis reaction, where two or more substances combine to form a more complex product.

Stoichiometry is the math behind chemistry. It's like a chef's recipe, where the quantity of each ingredient must be measured accurately to get the desired final dish. In terms of chemistry, stoichiometry allows us to calculate the amounts of reactants and products involved in a chemical reaction. It ensures that the law of conservation of mass is followed: the mass of reactants should equal the mass of the products.

To apply stoichiometry, one begins with a balanced chemical equation, just like the one provided in the solution: (H_2 + Br_2 -> 2HBr). This equation tells us that one molecule of hydrogen gas and one molecule of bromine gas react to form two molecules of hydrogen bromide. Using stoichiometry, we can determine how much of each reactant is needed and what amount of product can be expected from the reaction.

Chemical formulas are shorthand representations of molecules and compounds, much like initials are used for names. They tell us the type and number of atoms in a molecule. For instance, for hydrogen gas, the chemical formula is (H_2), indicating that two hydrogen atoms bond together. Similarly, bromine gas is denoted as (Br_2), representing a diatomic molecule consisting of two bromine atoms.

When balancing chemical equations, it’s crucial to pay attention to these formulas because they guide us in maintaining the same number of each type of atom on both sides of the equation. With this knowledge, the equation from the exercise was balanced by analyzing the chemical formula of hydrogen bromide ( (HBr)), understanding that it consists of one hydrogen atom and one bromine atom, and then using coefficients to match the atom counts on both sides of the reaction.