stoichiometry

Chemical Reactions and Equations

• Definition: Chemical reactions involve the transformation of substances through breaking and forming chemical bonds.

• Equations: Represent chemical reactions using molecular formulas and symbols.

Types of Equations

• Molecular Equation:

  • Shows the neutral formulas of all compounds regardless of their state in solution.

  • Example:

  • All substances represented in their molecular form whether soluble or insoluble.

• Complete Ionic Equation:

  • Represents all soluble strong electrolytes as ions.

  • Insulin compounds are shown in their molecular or solid state.

  • Example: Lead(II) nitrate and potassium chloride reacting to form lead(II) chloride and potassium nitrate with potassium and nitrate as spectator ions.

• Net Ionic Equation:

  • Results from removing spectator ions from the complete ionic equation.

  • Represents the actual chemical change occurring in the reaction.

  • Example: If

    • NaOH + HCl results in water and sodium chloride, the net ionic removes Na+ and Cl- since they do not change.

Spectator Ions

• Spectator ions are ions that do not participate in the reaction and remain unchanged on both sides of the equation.

• Example: Nitrate ions (

) are spectators in a reaction like:

• A + B → C + Na+

Double Replacement Reactions

• Definition: Reactions where two compounds exchange ions to form new compounds.

• Key characteristics:

  • Can produce gas, a precipitate, or a weak electrolyte.

  • Gas Evolution Reactions: Produce gas as one of the products, can be direct or indirect.

    • Example of direct:

      • Hydrochloric acid + potassium sulfide → hydrogen sulfide + potassium chloride.

    • Indirect:

      • Hydrochloric acid + sodium bicarbonate results in water and carbon dioxide through carbonic acid as an intermediate.

Reaction Products and Balancing

• Products can vary; if a product is soluble, it may not react further, while an insoluble product will precipitate out of the solution.

• Balancing equations is crucial to reflect the law of conservation of mass.

  • Example:

  • Magnesium carbonate with nitric acid produces carbon dioxide and water, which requires balancing.

Mole Ratios

• Definition: The ratios of coefficients in a balanced chemical equation that relate the amounts of reactants to products.

• Example:

  • From the equation: A + 2B → 2C,

    • 1 mole of A reacts with 2 moles of B to produce 2 moles of C.

• Use mole ratios to predict the amounts of products formed from given quantities of reactants.

  • Example: If 2.5 moles of magnesium chloride are present, the mole ratio can help find the moles of produced silver chloride.

  • Calculating using ratios:

  • Formula: (\text{Moles of Product} = \text{Moles of Reactant} \times \frac{\text{Coefficient of Product}}{\text{Coefficient of Reactant}})

Conclusion

• Chemical equations represent how reactants are transformed into products through observable reactions.

• Understanding the difference between molecular, complete ionic, and net ionic equations helps clarify the nature of chemical changes.