Chemical Equations and Reactions

Chemical Equations

• A chemical equation represents a chemical reaction using symbols and formulas of the reactants and products.
• Reactants are the substances that undergo a chemical change.
• Products are the substances that are formed as a result of the reaction.
• The arrow (→) separates the reactants from the products and indicates the direction of the reaction.
• The equation should be balanced, meaning that the number of atoms of each element is the same on both sides of the equation. This demonstrates the Law of Conservation of Mass.

Balancing Chemical Equations

• Balancing involves adjusting coefficients (numbers in front of the formulas) to ensure equal atoms of each element.
• Coefficients multiply all the atoms in the formula they precede.
• It is crucial to never change the subscripts (numbers within formulas) when balancing. Altering subscripts changes the identity of the substance.

Types of Chemical Reactions

• Synthesis (Combination): Two or more reactants combine to form a single product.
  • Example: 2H₂ + O₂ → 2H₂O (Formation of water)
• Decomposition: A single reactant breaks down into two or more simpler products.
  • Example: 2H₂O₂ → 2H₂O + O₂ (Decomposition of hydrogen peroxide)
• Single Replacement: One element replaces another element in a compound.
  • Example: Zn + 2HCl → ZnCl₂ + H₂ (zinc replacing hydrogen in hydrochloric acid)
• Double Replacement: The positive and negative ions of two compounds exchange partners to form two new compounds.
  • Example: AgNO₃ + NaCl → AgCl + NaNO₃ (Precipitation reaction – silver chloride forming a solid)
• Combustion: A substance rapidly reacts with oxygen, usually producing heat and light.
  • Example: CH₄ + 2O₂ → CO₂ + 2H₂O (Combustion of methane)

Representing States of Matter

• Indicate states using abbreviations in parentheses.
• (s) for solid
• (l) for liquid
• (g) for gas
• (aq) for aqueous solution (dissolved in water)
• Example: 2H₂(g) + O₂(g) → 2H₂O(l)

Stoichiometry

• Stoichiometry is the calculation of the quantities of reactants and products involved in a chemical reaction.
• It is based on the balanced chemical equation.
• Calculations relate moles of substances using the mole ratio from the coefficients.

Acid-Base Reactions (Neutralization)

• Acid-base reactions involve the transfer of protons (H⁺) between an acid and a base.
• Often result in the formation of water and a salt.
• Example: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Redox Reactions (Oxidation-Reduction)

• Involve the transfer of electrons between reactants.
• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Example: 2Na(s) + Cl₂(g) → 2NaCl(s) (Sodium is oxidized, chlorine is reduced)

Limiting Reactant

• In a chemical reaction, one reactant will be completely consumed before all the other reactants, limiting how much product can be made.
• Determine the limiting reactant by comparing the moles of each reactant to the stoichiometric ratio from the chemical equation.

Theoretical Yield, Actual Yield, and Percent Yield

• Theoretical yield is the maximum amount (in grams or moles) of product that can be formed from a given amount of reactant, assuming complete reaction.
• Actual yield is the amount of product isolated from a chemical reaction in a laboratory experiment.
• Percent yield is Actual Yield / Theoretical Yield * 100%. This indicates the efficiency of a reaction.

Chemical Equations and Reaction Mechanisms

• Different reactions can have different mechanisms (step-by-step pathways for the reaction).
• Equations do not always reflect the mechanisms involved.

Types of Chemical Reactions and their Properties

• Different reaction types have different characteristics.
• A reaction type can help with predicting outcomes or determining the products of a reaction.

Explore the principles of chemical equations, including how to balance them and the different types of chemical reactions. Learn about reactants, products, and the Law of Conservation of Mass. Perfect for chemistry students looking to solidify their understanding of these concepts.