4.2 Classifying Chemical Reactions

Chemical reactions are the heart of chemistry. They come in various types, each with unique characteristics and outcomes. Understanding these reactions helps us grasp how substances interact and transform in the world around us.

From precipitation to combustion, chemical reactions shape our daily lives. We'll explore how to classify and balance these reactions, predict their outcomes, and apply this knowledge to real-world situations. Let's dive into the fascinating world of chemical transformations!

Types of Chemical Reactions

Types of chemical reactions

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• Precipitation reactions involve the formation of an insoluble solid (precipitate) when two soluble compounds are combined occur when the product of the reaction is less soluble than the reactants ($AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$)
• ###Acid-Base_Reactions_0### involve the transfer of protons (H⁺) from an acid to a base acids donate protons, while bases accept protons ($HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$)
• Oxidation-reduction (redox) reactions involve the transfer of electrons between species oxidation is the loss of electrons, while reduction is the gain of electrons ($2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)$)

Classification of reactions

• Synthesis (combination) reactions: Two or more reactants combine to form a single product ($2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$)
• Decomposition reactions: A single compound breaks down into two or more simpler substances ($2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$)
• Single displacement reactions: One element replaces another element in a compound ($Zn(s) + 2HCl(aq) \rightarrow [ZnCl_2](https://www.fiveableKeyTerm:ZnCl_2)(aq) + H_2(g)$)
• Double displacement reactions: Two compounds exchange ions to form two new compounds ($BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$)
• Combustion reactions: A substance reacts with oxygen to produce heat, light, and often carbon dioxide and water ($CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$)

Chemical Equations and Stoichiometry

• Chemical equations represent reactions using symbols and formulas, showing reactants and products
• Balanced equations have equal numbers of atoms for each element on both sides
• Stoichiometry uses balanced equations to calculate quantities of reactants and products
• Reaction mechanisms describe the step-by-step process of a chemical reaction

Acids, Bases, and Solubility

Acids and bases in daily life

• Common acids found in everyday substances include citric acid (lemons, limes), acetic acid (vinegar), carbonic acid (carbonated beverages), and hydrochloric acid (stomach acid)
• Common bases found in everyday substances include sodium hydroxide (lye, drain cleaner), ammonia (cleaning products), calcium hydroxide (lime, antacids), and sodium bicarbonate (baking soda)

Predicting precipitate formation

• Soluble compounds include most nitrates, acetates, and chlorides, as well as alkali metal and ammonium compounds
• Insoluble compounds include most sulfides, hydroxides, and phosphates, as well as carbonates (except alkali metals and ammonium)
• Exceptions to solubility rules:
  1. Silver, lead, and mercury(I) chlorides are insoluble
  2. Barium, strontium, and calcium sulfates are insoluble
  3. Sodium, potassium, and ammonium compounds are generally soluble

Oxidation states in compounds

• Oxidation state rules:
  1. Free elements have an oxidation state of 0
  2. Monatomic ions have an oxidation state equal to their charge
  3. In compounds, the sum of oxidation states of all atoms must equal 0
  4. In polyatomic ions, the sum of oxidation states of all atoms must equal the charge of the ion
• Common oxidation states:
  • Alkali metals: +1
  • Alkaline earth metals: +2
  • Hydrogen: +1 (except in metal hydrides, where it is -1)
  • Oxygen: -2 (except in peroxides, where it is -1, and in compounds with fluorine)
  • Halogens: -1 (except when bonded to oxygen or another halogen)