3.1.1 Conservation of Mass and Balanced Chemical Equations

In this lesson, we will explore the concept of conservationThe professional care, preservation, and restoration of archaeological materials and sites, often requiring scientific expertise. of mass and learn how to balance chemical equations to ensure the equation accurately represents the reactants and products.

The Law of Conservation of Mass

The law of conservation of mass states that in a closed system, the total mass remains constant before and after a chemical reaction. This means that the total mass of the reactants must be equal to the total mass of the products. At the atomic level, this law implies that no atoms are lost or created during a chemical reaction.

Balanced Chemical Equations

Chemical reactions are often represented by chemical equations. A balanced chemical equation ensures that the number of atoms of each element is the same on both sides of the equation. Balancing an equation involves adjusting the coefficients (numbers in front of the formulas) to achieve this balance.

Example: The combustion of methane (CH₄) with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O) can be represented by the equation:

CH₄ + O₂ → CO₂ + H₂O

Balancing the equation:

The equation is unbalanced because there are different numbers of atoms on each side. To balance it, we can start by counting the number of atoms for each element:

• Carbon (C): 1 on the left, 1 on the right
• Hydrogen (H): 4 on the left, 2 on the right
• Oxygen (O): 2 on the left, 3 on the right

Balancing the carbon atoms:

We need 1 carbon atom on each side, so we place a coefficient of 1 in front of CO₂:

CH₄ + O₂ → 1CO₂ + H₂O

Balancing the hydrogen atoms:

We need 2 hydrogen atoms on each side, so we place a coefficient of 2 in front of H₂O:

CH₄ + O₂ → 1CO₂ + 2H₂O

Balancing the oxygen atoms:

We have 2 oxygen atoms on the left side and 5 oxygen atoms on the right side. To balance the oxygen atoms, we place a coefficient of 5/2 (or 2.5) in front of O₂:

CH₄ + 2.5O₂ → 1CO₂ + 2H₂O

Final balanced equation:

The final balanced equation is:

CH₄ + 2.5O₂ → CO₂ + 2H₂O

Use of Multipliers in Equations

In chemical equations, multipliers are used to balance the number of atoms. The multipliers can appear as normal script before a formula or as a subscript within a formula.

• Coefficients as multipliers: Coefficients are placed in front of formulas to indicate the number of molecules or moles involved in the reaction. They apply to all atoms within the formula.
• Subscripts as multipliers: Subscripts are written within formulas and indicate the number of atoms of an element within a molecule. They do not affect the balance of the equation and should not be changed during the balancing process.

Conclusion

The law of conservation of mass states that no atoms are lost or created during a chemical reaction, ensuring that the mass of the reactants is equal to the mass of the products. Balancing chemical equations is crucial to accurately represent the reactants and products, ensuring that the number of atoms of each element is the same on both sides of the equation.