Write balanced chemical equations for the following reactions: (a) metallic aluminum burned in air (b) elemental aluminum heated in an atmosphere of chlorine (c) aluminum heated in hydrogen bromide gas (d) aluminum hydroxide added to a solution of nitric acid

A chemical reaction is a process where substances, known as reactants, transform into new substances called products. During a chemical reaction, the bonds between atoms in the reactants are broken and new bonds form to create the products. This transformation often involves the exchange or sharing of electrons and can release or absorb energy.

For example, when metallic aluminum burns in air (reaction a), aluminum reacts with oxygen to form aluminum oxide. This is a combustion reaction, a type of chemical reaction, where oxygen combines with another element to produce oxides. These reactions are fundamental to our understanding of chemistry and are one of the various ways that new substances are formed.

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It is based on the law of conservation of mass, which states that matter cannot be created nor destroyed in a chemical reaction. Stoichiometry involves calculating the amounts of reactants needed or products formed in a chemical reaction.

In the provided exercise, stoichiometry comes into play when ensuring that we have the correct amount of each substance. For instance, in the reaction of aluminum with hydrogen bromide gas (reaction c), we see that the stoichiometry is essential to predicting that two moles of aluminum react with six moles of hydrogen bromide to produce two moles of aluminum bromide and three moles of hydrogen gas. These mole ratios are determined by the coefficients in the balanced chemical equation.

A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants on the left side, the products on the right side, and an arrow pointing from reactants to products to indicate the direction of the reaction. Chemical equations must be balanced so that they obey the law of conservation of mass; this means that for each element involved in the reaction, the total number of atoms for that element must be the same on both sides of the equation.

For example, equation (d) shows the reaction of aluminum hydroxide with nitric acid to produce aluminum nitrate and water. Initially written as an unbalanced equation, it must be adjusted to accurately reflect the matter conservation by ensuring the number of atoms of each element is equal on both sides. Balancing this chemical equation provides insight into the reaction's stoichiometry—specifically, how much of each reactant is needed and how much of each product is produced.

In the context of a chemical equation, reactants are the starting substances that undergo change, and products are the substances that are formed as a result of the chemical reaction. The reactants are found on the left side of a chemical equation, while the products are on the right.

Looking at reaction (b) as an illustration, elemental aluminum and chlorine gas are the reactants, and they undergo a chemical change to become aluminum chloride, the product. Understanding the relationship between reactants and products is crucial not only for writing balanced chemical equations but also for predicting the outcome of the reaction and performing stoichiometric calculations to determine how much product can be expected from a given amount of reactants.