Question

What do the subscripts in a chemical formula represent? What do the coefficients in a balanced chemical equation represent?

Short answer

Subscripts in a chemical formula indicate the number of atoms of each element present in a molecule or formula unit of a compound, such as \(H_2O\) having two hydrogen atoms and one oxygen atom. Coefficients in a balanced chemical equation represent the number of molecules or formula units of each substance involved in the reaction, such as \(2H_2 + O_2 -> 2H_2O\) showing that two molecules of hydrogen and one molecule of oxygen react to form two molecules of water.

Step-by-step solution

Explanation of Subscripts in a Chemical Formula

In a chemical formula, subscripts are used to indicate the number of atoms of each element present in one molecule or formula unit of a compound. For example, in the formula for water, \(H_2O\), the subscript '2' after the element hydrogen (H) means that there are two hydrogen atoms in one molecule of water, and the absence of a subscript after the element oxygen (O) means that there is one oxygen atom in one molecule of water.

Explanation of Coefficients in a Balanced Chemical Equation

In a balanced chemical equation, coefficients are the numbers placed in front of the chemical formulas to indicate the number of molecules or formula units of each substance involved in the reaction. Coefficients are necessary to balance both the atoms and charge in a chemical equation. For example, in the balanced chemical equation for the reaction between hydrogen and oxygen to form water: \[2H_2 + O_2 -> 2H_2O\] The coefficient '2' in front of the formula for hydrogen (\(H_2\)) indicates that there are two molecules of hydrogen taking part in the reaction, and the coefficient '2' in front of the formula for water (\(H_2O\)) indicates that two molecules of water are produced in the reaction. The absence of a coefficient in front of the formula for oxygen (\(O_2\)) means that one molecule of oxygen is involved in the reaction. In conclusion, subscripts in a chemical formula represent the number of atoms of each element present in a molecule or formula unit of a compound, while coefficients in a balanced chemical equation represent the number of molecules or formula units of each substance involved in the reaction.

Key concepts

Subscripts in Chemistry

In chemistry, subscripts are a crucial part of chemical formulas. They are the small numbers found just below and to the right of a chemical symbol within a compound formula. These numbers tell us how many atoms of that element are present in a single molecule or unit of the compound.
For example, in the chemical formula for water, \(H_2O\), the subscript '2' after hydrogen indicates that each water molecule contains two hydrogen atoms. The absence of a subscript next to the oxygen (O) tells us there is only one oxygen atom in a molecule of water. This is implicit when only one atom is involved; often, the number '1' is simply not written.
Subscripts are essential because they define the specific amount of each element within a compound. Changing them changes the entire substance – for example, \(H_2O_2\) represents hydrogen peroxide instead of water. Therefore, the role of subscripts in chemistry is fundamental to the identity and composition of chemical compounds.

Coefficients in Chemical Equations

Coefficients in chemical equations are the large numbers written in front of a chemical formula in a reaction equation. Their job is to show how many molecules or moles of each substance are involved in the reaction. These coefficients ensure that the equation is balanced, meaning the same number of each type of atom is present on both sides of the equation.
For example, consider the balanced chemical reaction for forming water from hydrogen and oxygen:

• \(2H_2 + O_2 \rightarrow 2H_2O\)

Here, the coefficient '2' before \(H_2\) indicates two molecules of hydrogen are used, and '2' before \(H_2O\) denotes two molecules of water are produced. This ensures all hydrogen atoms from one side are accounted for on the other.
Understanding coefficients is crucial because they help us comprehend how substances interact in a reaction and confirm that conservation of mass is maintained, as matter cannot be created or destroyed during chemical reactions.

Balanced Chemical Equations

A balanced chemical equation represents a chemical reaction with the same number of atoms for each element on both sides of the equation. This mirrors the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
To balance an equation, we adjust the coefficients—those numbers in front—rather than changing the subscripts in the formulas. Changing the subscripts alters the substances involved, while manipulating coefficients adjusts the number of units participating in the reaction.
Balancing chemical equations ensures that reactions are accurately depicted. For example, in the conversion:

• \( C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O \)

The balanced equation shows that every molecule of propane \(C_3H_8\) reacts with five molecules of oxygen \(O_2\), producing three molecules of carbon dioxide \(CO_2\) and four molecules of water \(H_2O\). Each element is accounted for, ensuring that the reaction is environmentally sustainable and mathematically sound.