The following reaction of A₃ molecules is spontaneous. (a) Write a balanced equation for the reaction.

A balanced chemical equation represents a chemical reaction where the number of atoms for each element is the same on both the reactant and product sides. This is achieved by adjusting the coefficients in front of the chemical formulas. Balancing is crucial as it adheres to the law of conservation of mass, ensuring that matter is neither created nor destroyed during the reaction.

The spontaneity of a reaction refers to its ability to occur without external influence once initiated. This is often determined by changes in Gibbs free energy (ΔG); a negative ΔG indicates a spontaneous process. Factors such as enthalpy, entropy, and temperature play significant roles in assessing whether a reaction will proceed spontaneously.

Understanding the molecular composition of reactants is essential for writing balanced equations. In this case, A₃ indicates that each molecule consists of three atoms of element A. Recognizing the molecular structure helps in predicting how these molecules will interact and combine during the reaction, which is vital for accurately representing the reaction in a balanced equation.