Introductory Chemistry: Basic Principles of Chemical Reactions

Overview of Chemical Reactions

• Exploration of basic principles of chemical reactions
• Recognition of when a reaction takes place based on visual and physical clues
• Understanding conventions for writing chemical equations
  • Importance of balancing equations in accordance with the law of conservation of mass

Nature of Chemical Reactions

• Involves substances in specific states of matter depending on conditions
• Example: Saltwater and ice mixture
  • Solid ice: H2O (S)
  • Liquid water: H2O (L)
  • Evaporated water: H2O (G)
  • Dissolved sodium chloride: NaCl (Aq)

Identifying Chemical Reactions

• A chemical reaction occurs when substances transform into new substances
• Clues indicating a reaction:
  • Changes in color
  • Formation of solid (precipitate)
  • Generation of bubbles (gas)
  • Absorption or generation of heat
  • Flame production
• Example: Hydrogen and oxygen reaction producing water vapor with significant heat

Writing Chemical Equations

• Chemical equations describe reactions including physical states and ratios of reactants and products
• Coefficients indicate the ratios
  • No number means a coefficient of 1
  • Example: 2 H2 + O2 → 2 H2O (g)
• Energy input/output in reactions (e.g., battery reaction in water)

Components of Chemical Equations

• Reactants: left side of the arrow
• Products: right side of the arrow
• Arrow indicates change and formation of new substances
• Balanced equations must show equal numbers of each atom type on both sides
• Conservation of mass principle: mass is neither created nor destroyed

Balancing Chemical Equations

• Example: Sodium and chlorine reaction
  • Unbalanced: Na + Cl2 → NaCl
  • Balanced: 2 Na + Cl2 → 2 NaCl
• Each atom type must be accounted for in balancing
• Coefficients are used, subscripts should not be changed

Steps for Balancing Equations

1. Identify reactants and products
2. Write unbalanced equation
3. Add coefficients to balance the equation
4. Confirm all atoms are balanced

• Example: Balancing the combustion of methane (CH4)
  • Equation: CH4 + 2 O2 → CO2 + 2 H2O

Practice Balancing Equations

• Iterative process of adjusting coefficients as necessary
• Example: Balancing calcium oxide and carbon to produce calcium carbide and carbon dioxide
• Always check for balanced atoms and correct coefficients

Summary

• Balancing chemical equations is essential for understanding chemical reactions
• Practice is key to mastering this skill
• Use the smallest whole number integers possible for coefficients
• Balance equations to reflect both macroscopic laboratory observations and microscopic molecular transformations.