Chemical Reactions

Evidence of Chemical Reactions Chemical Reaction: The process by which the atoms of one or more substances are rearranged to form different substances. Temperature change Color change Gas or solid appears

Representing Chemical Reactions Symbol Meaning + Separates two or more products or reactants → Separates reactants from products (s) Solid State (l) Liquid State (g) Gaseous State (aq) Identifies water solution Chemical Equation Reactants: substances reacting; on left side Products: substances produced; on right side

Representing Chemical Reactions How would you write an equation for sodium reacting with chloride to make sodium chloride? Reactant 1 + Reactant 2 → Product 1 sodium + chloride → sodium chloride Na (s) + Cl2 (g) → NaCl (s)

Representing Chemical Reactions Law of Conservation of Mass: atoms cannot be created or destroyed. All atoms in reactants must be in products, and visa versa Balancing the equation Na (s) + Cl2 (g) → NaCl (s) Can not occur without coefficients: number written in front

Balancing Equations Write Equation Count atoms in of elements in reactants Count atoms of elements in products Change the coefficients to make # of atoms equal Write coefficients in their lowest ratio Check

Balancing Equations Na (s) + Cl2 (g) → NaCl (s) H2 (g) + O2 (g) → H2O (l) AgNO3(aq) + Cu(s) → CuNO3(aq) + Ag Al(s) + O2(s) → Al2O3

Classifying Chemical Reactions 5 types Need to be able to recognize different types. Need to be able to predict products of different types of reactions

Synthesis Reactions A chemical reaction in which two or more substances react to produce a single product. A + B → AB Na (s) + Cl2 (g) → NaCl (s) Compounds combining is also synthesis CaO(s) + H2O(l) → Ca(OH)2

Combustion Reaction Oxygen combines with a substance to produce heat and energy 2H2(g) + O2(g) → 2H2O(g) All combustion are synthesis not all synthesis are combustion.

Combustion Reaction CH4, methane, is a hydrocarbon hydrocarbon + oxygen → carbon dioxide + water CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) Can be tough to balance, always balance O2 last.

Decomposition Reactions Single compound breaks down into two or more elements or compounds. AB → A + B Often requires an energy source. NH4NO3(s) → N2O(g) + 2H2O(g) Air Bags 2NaN3(s) → 2Na(s) + 3N2(g)

Single Replacement Reactions A reaction in which the atoms of one element replace the atoms of another A + BX → AX + B Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)

Double Replacement Reactions Exchange of ions between two compounds AX + BY → AY + BX Ca(OH)2 (aq) + 2HCl (aq) → CaCl2 (aq) + 2 H2O(l) All double replacement reactions produce either a precipitate, a gas, or water

Double Replacement Reactions Precipitate: a solid being produced during a chemical reaction in a solution Pair cations with other anion for both compounds LiI(aq) + AgNO3(aq) →

Types of reactions