Chemical Equations and the Law of Conservation of Mass

Introduction to Chemical Equations

Chemical equations are symbolic representations of chemical reactions, showing the reactants and products involved. They are essential for understanding how substances interact and transform during chemical processes.

• Chemical Reaction: A process in which substances (reactants) are rearranged to form new substances (products).

• Chemical Equation: An expression using chemical formulas to represent the reactants and products in a reaction.

• Example:

Law of Conservation of Mass

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.

• Key Principle: Atoms are conserved in chemical reactions; they are simply rearranged.

• Balanced Equation: Each side of the equation must have the same number of each type of atom.

• Example: In , there are 4 H atoms and 2 O atoms on both sides.

Stoichiometry

Stoichiometry is the area of chemistry that examines the quantitative relationships between reactants and products in chemical reactions.

• Definition: The calculation of the quantities of reactants and products involved in a chemical reaction.

• Key Terms: Element, Molecule, Mass

• Historical Note: Antoine Lavoisier established the law of conservation of mass.

Balancing Chemical Equations

Steps to Balance Equations

Balancing chemical equations ensures that the law of conservation of mass is obeyed. This involves adjusting coefficients so that the number of atoms of each element is the same on both sides.

• Unbalanced Equation: The number of atoms for each element is not equal on both sides.

• Balanced Equation: Coefficients are used to equalize atom counts.

• Example: (unbalanced)

• Balanced:

Symbols in Chemical Equations

• (s): Solid

• (l): Liquid

• (g): Gas

• (aq): Aqueous (dissolved in water)

• Δ (delta): Indicates heat is added

• hv: Indicates light is added

Types of Chemical Reactions

Combination (Synthesis) Reactions

Combination reactions involve two or more reactants forming a single product.

• General Form:

• Example:

Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more products.

• General Form:

• Example:

• Applications: Used in airbags, explosives, and other rapid energy release processes.

Combustion Reactions

Combustion reactions are rapid reactions with oxygen that produce a flame, usually forming and as products.

• General Form: Hydrocarbon +

• Example:

• Applications: Burning fuels, energy production, metabolism of glucose in the body.

Oxidation Reactions

Oxidation reactions involve the transfer of electrons, often seen in combustion and other redox processes.

• Example:

Stoichiometric Calculations

Using Moles and Molar Mass

Stoichiometric calculations use the balanced chemical equation to relate the amounts of reactants and products.

• Mole: The amount of substance containing entities (Avogadro's number).

• Molar Mass: The mass of one mole of a substance, in grams per mole ().

• Example Calculation: To find the mass of produced from g of a hydrocarbon, use the balanced equation and molar masses.

Sample Stoichiometry Table

The following table summarizes the steps for stoichiometric calculations:

Summary of Key Equations

• General Stoichiometry:

• Law of Conservation of Mass:

Additional info:

• Some context and examples were inferred to clarify fragmented notes and images.

• Applications such as airbags, fuel cells, and metabolism were added for academic completeness.