Chapter 2: Fundamental Laws of Chemistry

Law of Conservation of Mass

The Law of Conservation of Mass states that the total mass of substances present before a chemical reaction is equal to the total mass of substances after the reaction. This principle is foundational in chemistry and is essential for understanding chemical reactions and stoichiometry.

• Definition: Mass is neither created nor destroyed in a chemical reaction.

• Application: Used to balance chemical equations and calculate reactant/product quantities.

• Example: When burning magnesium in air, the mass of magnesium plus the mass of oxygen consumed equals the mass of magnesium oxide produced.

Law of Constant Composition (Definite Proportions)

The Law of Constant Composition (also called the Law of Definite Proportions) states that all samples of a given compound have the same elemental composition by mass.

• Definition: A chemical compound always contains the same elements in the same proportion by mass.

• Example: Water (H2O) always contains hydrogen and oxygen in a mass ratio of approximately 1:8, regardless of the source.

• Chemical Formula: Indicates the elements present and their relative quantities (e.g., H2O).

Law of Multiple Proportions

The Law of Multiple Proportions states that if two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

• Definition: When elements A and B form more than one compound, the different masses of B that combine with a fixed mass of A are in a ratio of small whole numbers.

• Example: Carbon and oxygen form both carbon monoxide (CO) and carbon dioxide (CO2):

  • CO: 12 g C combines with 16 g O

  • CO2: 12 g C combines with 32 g O

  • Ratio of oxygen masses: 16:32 = 1:2

Atomic Theory

The Atomic Theory provides a framework for understanding the composition and behavior of matter at the atomic level.

• 1. Each chemical element is composed of atoms: Atoms are the indivisible particles that make up elements.

• 2. All atoms of a given element are alike: Atoms of the same element have identical properties.

• 3. Compounds are formed by the combination of atoms of different elements in simple numerical ratios: For example, AB, A2B, AB2, etc.

Basic Chemical Calculations

Unit Conversions and Density Calculations

Unit conversions are essential in chemistry for expressing quantities in appropriate units. Density is a common property used to relate mass and volume.

• Example Problem: What is the mass of 7.5 L of water? (Density, )

• Step 1: Convert volume to cubic meters:

  • (since )

• Step 2: Convert density to kg/m3:

• Step 3: Calculate mass:

Volume and Diameter of a Spherical Cell

To find the diameter of a spherical object (such as a red blood cell) given its volume, use the formula for the volume of a sphere:

• Formula:

• Given:

• Solving for diameter (d = 2r):

• Example Calculation:

  • Calculate , then in cm, and convert to mm ()

Exponent Rules

Exponent rules are frequently used in scientific notation and unit conversions.

• Power of a Power:

• Multiplying Exponents:

Atomic Weights and Relative Mass Calculations

Atomic weights represent the relative masses of different elements and are used to determine the proportions in which elements combine.

• Example: If 1.444 g of potassium reacts with 8.178 g of chlorine, and 6.867 g of chlorine is left unreacted, the mass of potassium chloride formed is:

Summary Table: Fundamental Laws of Chemistry

Additional info: Some calculations and examples have been expanded for clarity and completeness. The notes cover essential introductory concepts in general chemistry, including foundational laws, atomic theory, and basic quantitative problem-solving.