# 1.6: Chemical Reaction- An Example of a Chemical Change


Chemical reactions are the processes by which chemicals interact to form new chemicals with different compositions. Simply stated, a chemical reaction is the process where reactants are transformed into products. How chemicals react is dictated by the chemical properties of the element or compound- the ways in which a compound or element undergoes changes in composition.

Chemical reactions are constantly occurring in the world around us; everything from the rusting of an iron fence to the metabolic pathways of a human cell are all examples of chemical reactions. Chemistry is an attempt to classify and better understand these reactions. One key reaction in modern civilization is combustion

A chemical reaction is typically represented by a chemical equation, which represents the change from reactants to products. The left hand side of the equation represents the reactants, while the right hand side represents the products. A typical chemical reaction is written with stoichiometric coefficients, which show the relative amounts of products and reactants involved in the reaction. Each compound is followed by a parenthetical note of the compound’s physical state: $$(l)$$ for liquid, $$(s)$$ for solid, $$(g)$$ for gas. The symbol $$(aq)$$ is also commonly used in order to represent an aqueous solution, in which compounds are dissolved in water.

Butane is a gas at room temperature and atmospheric pressure and is highly flammable, colorless, easily liquefied gas (under light pressure). Butane can be used for gasoline blending, as a fuel gas, fragrance extraction solvent, either alone or in a mixture with propane, and as a feedstock for the manufacture of ethylene and butadiene, a key ingredient of synthetic rubber. The chemical formula of butane if $$\ce{C4H10}$$. When oxygen is plentiful, butane burns to form carbon dioxide and water vapor as observed in modern lighters (Figure $$\PageIndex{1}$$).

This reaction in words is

$\text{butane} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}$

and the corresponding chemical equation for this reaction is

$\ce{2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)}$

In the above chemical equation, $$\ce{C4H10}$$ and $$\ce{O2}$$ are the reactants that reacted to form the products: $$\ce{CO2}$$ and $$\ce{H2O}$$,

Writing Chemical Equations

To write an accurate chemical equation, two things must occur:

1. Each product and reactant must be written using its chemical formula
2. Coefficients are used in front of the chemical formulas to reflect the ratio species (discussed in Chapter 2)
3. Adding the phase of each chemical in parentheses (although this is often dropped for convience)