Representations of Reactions

Chapter: Representations of Reactions

Understanding Chemical Reactions

  • A chemical reaction is a process that involves the change of substances into new substances.
  • Chemical reactions can be represented in several ways including word equations, symbol equations, and energy level diagrams.
  • Symbols and formulas are used to write chemical equations that represent chemical reactions.

Word Equations

  • A word equation represents a chemical reaction using words to describe the reactants (the starting substances) and the products (the substances formed in the reaction).
  • By using words, this representation can be easily understood even without knowledge of chemical symbols.

Symbol Equations

  • A symbol equation represents a chemical reaction using the symbols and formulas of the reactants and products.
  • Symbol equations must be balanced, to comply with the law of conservation of mass. This law states that matter cannot be created nor destroyed in a chemical reaction.
  • In a balanced symbol equation, the number of atoms for each element is the same on the reactants side as on the products side.

Energy Level Diagrams

  • An energy level diagram is a graphical representation of the energy changes that occur during a chemical reaction.
  • Energy is depicted on the vertical axis, while the time of reaction or progress of reaction is plotted on the horizontal axis.
  • This diagram helps visualise the energy changes, showing whether a reaction is endothermic (absorbs energy) or exothermic (releases energy).

State Symbols and Half-Equations

  • State symbols (s, l, g, aq) indicate the physical state (solid, liquid, gas or aqueous solution) of each substance in a chemical equation.
  • Half-equations show the oxidation or reduction of species separately. In a half-equation, the number of atoms and the charge must balance.
  • Oxidation refers to a process where a substance loses electrons, while reduction refers to a process where a substance gains electrons.

Note: Familiarity with these representations of reactions and understanding the clues each one provides about a chemical reaction will refine your ability to comprehend and discuss chemical phenomena.