Write a balanced chemical equation for the reactions given below: a. When hydrogen gas reacts is combined with oxygen gas and the mixture ignited with a spark, water is formed in a violent reaction. b. Lead (IV) oxide reacts with HCl to give lead (II) chloride, chlorine gas and water. c. Solid potassium chlorate decomposes on heating to form solid KCl and oxygen gas.

A chemical reaction is a process where substances, known as reactants, are transformed into different substances called products. This transformation occurs as a result of the breaking and forming of chemical bonds. Consider the example of burning hydrogen gas in the presence of oxygen, which is reaction (a) from the exercise. When ignited, hydrogen and oxygen react violently to form water, showcasing the exothermic nature of the reaction where energy, in the form of heat or light, is also released.

Understanding chemical reactions is foundational to the study of chemistry, as they explain how new substances are formed and can illustrate the conservation of matter, where the total mass of reactants equals the total mass of products.

Stoichiometry is essentially the arithmetic of chemistry. It involves the calculation of the quantitative (measurable and numerical) relationships of the elements and compounds as they participate in chemical reactions. The term comes from the Greek words 'stoicheion' (element) and 'metron' (measure). For instance, when balancing reaction (c), the stoichiometry of the decomposition of potassium chlorate is taken into account to ensure that the number of atoms for each element is preserved on both sides of the equation.

Proper stoichiometry is crucial for predicting the amounts of products formed in a given chemical reaction or the amounts of reactants needed for a reaction to proceed completely. This concept is not only central to the field of chemistry but also critically important in various practical applications such as pharmaceuticals, environmental engineering, and industrial chemistry.

A chemical equation is a symbolic representation of a chemical reaction where the reactants are placed on the left side and the products on the right, separated by an arrow indicating the direction of the reaction. For example, in reaction (b), the lead (IV) oxide reacts with HCl to give lead (II) chloride, chlorine gas, and water, depicted by the equation \[ \text{PbO}_2 + 4\text{HCl} \rightarrow \text{PbCl}_2 + \text{Cl}_2 + 2\text{H}_2\text{O} \].

A balanced chemical equation ensures that the number of atoms for each element is the same on both sides, adhering to the law of conservation of mass. Balancing equations is a fundamental skill in chemistry that enables scientists and students to understand the ratio in which substances react and form products.

A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more simpler substances. This breakdown can be induced by heat, light, or electricity. In the context of our exercise, reaction (c) is a classic example, where solid potassium chlorate decomposes upon heating to form solid potassium chloride and oxygen gas. The balanced chemical equation, \[ 2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2 \], illustrates how the breakdown of one compound, potassium chlorate, leads to the formation of two distinct products, showcasing the principle of a decomposition reaction.

Decomposition reactions are often used to extract metals from their ores or to produce simpler substances as precursors for further chemical processing. Understanding and balancing these reactions are vital in both academic and applied chemical studies.