Chemistry: Law of Conservation of Mass

Law of Conservation of Mass

Chemical Reactions

• The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction.
• The total mass of reactants equals the total mass of products.
• Atom economy: the number of atoms of each element is conserved during a chemical reaction.
• Chemical equations must be balanced to reflect the law of conservation of mass.

Physical Changes

• The law of conservation of mass also applies to physical changes, such as phase transitions (e.g., melting, boiling).
• Matter changes form, but its mass remains constant.
• Examples: ice → water → steam; solid → liquid → gas.

Stoichiometry

• Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions.
• The law of conservation of mass is the foundation of stoichiometry.
• Stoichiometric coefficients: whole numbers that balance a chemical equation, ensuring the law of conservation of mass is upheld.
• Applications: calculation of reactant and product quantities, limiting reagents, and percent yield.

Law of Conservation of Mass

• Matter cannot be created or destroyed in a chemical reaction, only converted from one substance to another.
• The total mass of reactants is equal to the total mass of products, ensuring mass is conserved.
• Atom economy is the principle that the number of atoms of each element is conserved during a chemical reaction.

Balancing Chemical Equations

• Chemical equations must be balanced to reflect the law of conservation of mass.
• Stoichiometric coefficients are whole numbers that balance a chemical equation, ensuring the law of conservation of mass is upheld.

Physical Changes

• The law of conservation of mass also applies to physical changes, such as phase transitions (e.g., melting, boiling).
• Matter changes form, but its mass remains constant during physical changes.
• Examples of physical changes include ice → water → steam, and solid → liquid → gas.

Stoichiometry

• Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions.
• The law of conservation of mass is the foundation of stoichiometry.
• Applications of stoichiometry include calculation of reactant and product quantities, limiting reagents, and percent yield.

Phase Transition

• A phase transition is a physical change where a substance changes from one state of matter to another due to altered intermolecular forces between molecules.

Types of Phase Transitions

• Melting: solid to liquid
• Freezing: liquid to solid
• Vaporization: liquid to gas
• Condensation: gas to liquid
• Sublimation: solid to gas
• Deposition: gas to solid

Characteristics of Phase Transitions

• Reversible: substances can change back to their original state
• Thermodynamic: phase transitions occur at specific temperatures and pressures dependent on the substance
• Orderly: molecules arrange themselves in a specific pattern during a phase transition

Factors Affecting Phase Transitions

• Temperature: phase transition temperature depends on the substance
• Pressure: changes in pressure can affect the phase transition temperature
• Surface Tension: energy at the surface of a substance can affect the phase transition

Examples of Phase Transitions

• Water: solid (ice) → liquid (water) → gas (water vapor)
• Carbon Dioxide: solid (dry ice) → gas (carbon dioxide)

Solid State

• Fixed shape and volume
• Particles are closely packed with a fixed position, vibrating in place
• Examples: rocks, metals, ice
• Characteristics:
  • Rigid and unchanging shape
  • Definite volume
  • Low kinetic energy particles
  • Difficult to compress

Liquid State

• Takes the shape of its container
• Fixed volume, but not a fixed shape
• Particles are close together, free to move past one another
• Examples: water, oil, juice
• Characteristics:
  • Takes the shape of its container
  • Definite volume
  • Moderate kinetic energy particles
  • Can be compressed slightly

Gas State

• Neither a fixed shape nor a fixed volume
• Particles are widely spaced, free to move randomly
• Examples: air, helium, oxygen
• Characteristics:
  • Takes the shape and volume of its container
  • No definite shape or volume
  • High kinetic energy particles
  • Easy to compress