A sample of limestone \(\left(\mathrm{CaCO}_{3}\right)\) is heated in a closed vessel until it is partially decomposed. Write an equation for the reaction and state how many phases are present.

Understanding the process of chemical reactions is fundamental in studying chemistry. A chemical reaction involves the transformation of one or more substances into new products. In a reaction, the starting substances, known as reactants, go through a chemical change that yields new products.

In the given exercise, the reaction is a type of chemical reaction called decomposition. Decomposition reactions occur when one compound breaks down into two or more simpler substances when energy, in this case, heat, is supplied. The decomposition of limestone when heated forms calcium oxide and carbon dioxide: \[\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)\].

This reaction showcases the conversion of a single solid reactant into a solid and a gaseous product. The brackets indicate the states of matter for each compound: (s) for solids and (g) for the gas, which is an integral part of understanding chemical equations.

Chemistry is deeply rooted in the study of states of matter, the distinct forms that different phases of matter take on. The four fundamental states are solid, liquid, gas, and plasma. In our limestone decomposition example, there are two states of matter involved: solid and gas.

Distinguishing States of Matter

The limestone (\(\text{CaCO}_3\)) and calcium oxide (\(\text{CaO}\)) are in a solid state, usually characterized by definite shape and volume due to the fixed positions of their particles. In contrast, carbon dioxide (\(\text{CO}_2\)), the other product, is in a gaseous state, where particles move freely and occupy the entire volume of the container.
In the context of the provided reaction, the solid and gas states are clearly differentiated, which is critical in predicting the behavior of substances during reactions.

The quantitative study of reactants and products in a chemical reaction is known as stoichiometry. It allows us to calculate masses, volumes, and moles, and to understand the relationship between different compounds in a reaction.

Using stoichiometry, we can determine the amount of products formed from given quantities of reactants. In this limestone reaction, stoichiometry can tell us how much limestone is needed to produce a certain amount of calcium oxide and carbon dioxide. The balanced reaction equation provided, which illustrates a one-to-one-to-one mole ratio, is the starting point for these calculations: \[1 \text{ mole CaCO}_3 → 1 \text{ mole CaO} + 1 \text{ mole CO}_2\].
Students often use stoichiometry in laboratory settings to predict the outcomes of experiments, ensuring that reactants are used efficiently and wastage is minimized.