Chemical Reactions

Which of the following are examples of chemical change? Digestion Melting an ice cube Running a car Decomposition Dissolving sugar in water Boiling water Photosynthesis Cellular Respiration A nail rusting

Chemical Reaction (or Chemical Change) The process by which the atoms of one or more substances are REARRANGED to form different substances

Evidence of a Chemical Reaction 1.Temperature change Exothermic Reaction-heat is given off Endothermic Reaction-heat is absorbed Endothermic Reaction Exothermic Reaction

Classify each of the following as endothermic or exothermic. A log burning in the fireplace. A chemical ice pack Baking soda is added to vinegar causing the test tube to become cold to the touch. A hand warmer Drain cleaner is added to a clogged pipe causing the pipes to become warm. Photosynthesis Cellular respiration Baking a cake

Evidence of a Chemical Reaction 2.Color Change

Evidence of a Chemical Reaction 3.Production of an Odor

Evidence of a Chemical Reaction 4. Production of a gas (bubbles)

Evidence of a Chemical Reaction 5. Formation of a solid called a precipitate

Evidence of a Chemical Reaction 6. Production of other forms of energy such as light.

Chemical equation A written expression of a chemical reaction Reactant  Product (Starting Substance ) (New substance that forms) Symbols used in chemical equations + Separates 2 or more reactants or products  Separates reactants from products (s)Solid state (l)Liquid state (g) Gaseous State (aq) Dissolved in water ∆ Heat is added

Chemical Equations Reaction: Solid aluminum reacts with liquid bromine to produce solid aluminum bromide. Word Equation-the description of a reaction is written according to the following format: Reactant 1 + Reactant 2  Product 1 Aluminum (s) + Bromine (l)  Aluminum Bromide (s)

Chemical Equations Word Equation Aluminum (s) + Bromine (l)  Aluminum Bromide (s) Skeleton Equation-formulas/symbols are used to represent names of compounds and elements. Al (s) + Br 2 (l)  AlBr 3 (s)

Practice writing word and skeleton equations: Write the equation for the reaction observed in lab. Write the equation for the endothermic reaction that was observed.

Chemical Equations A complete chemical equation is a statement that uses chemical formulas, states of matter and coefficients to represent the substances involved and how much is needed to fully react.

Balancing Chemical Equations A chemical equation is not complete until the atoms on the reactant side equal the atoms on the product side. COEFFICIENTS (NUMBERS IN FRONT OF THE FORMULA) are used to balance equations. ___Al (s) + ___Br 2 (l)  ___AlBr 3 (s)

Why must we balance equations? Law of conservation of mass-during chemical equations, matter cannot be created or destroyed. Atoms are only rearranged. Therefore, the number and kinds of atoms making up the reactants must be the same as those making up the products. Mass of reactants = Mass of products

Types of Chemical Reactions Synthesis Reactions- Two or more substances combine to form a single product General Form: A + B  AB Example N 2 (g) + 3H 2 (g)  2NH 3 (g) Na 2 O + H 2 O  2NaOH

Types of Chemical Reactions Decomposition Reactions- A single reactant breaks down into two or more elements or new compounds General Form: AB  A + B Example: NH 4 NO 3 (s)  N 2 O (g) + 2H 2 O (g) 2HgO  2Hg + O 2

Types of Chemical Reactions Single Replacement reactions- Atoms of one element replace atoms of another element in a compound General Form: A + BC  B + AC Metals replace metals and nonmetals replace nonmetals Example: Cu(s) + AgNO 3 (aq)  2Ag(s) + Cu(NO 3 ) 2 (aq) Cu (metal) replaces Ag (metal) in the compound because it is more reactive. Cl 2 + NaBr  Br 2 + NaCl Cl 2 (nonmetal) replaces Br 2 (nonmetal) because it is more reactive.

Types of Chemical Reactions How do I know if an one atom can replace another? There is a table of reactivity. It ranks metals from most reactive (at the top) to least reactive (at the bottom)

Reactivity Table Most Active MetalsLi Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Least Active MetalsPt Au Most Active Nonmetals F Cl Br I Least Active Nonmetals

Which of the following reactions can take place? I 2 + NaF  F 2 + NaI Mg + HCl  MgCl 2 + H 2 Cu + MgSO 4  CuSO 4 + Mg K + NaOH  KOH + Na

Types of Chemical Reactions Double Replacement Reactions- Atoms in one compound replace atoms in another compound General Form: AB + CD  AD + CB NaOH (aq) + CuCl 2 (aq)  2NaCl(aq) + Cu(OH) 2 (s)

Types of Chemical Reactions Combustion Reaction- Combustion reactions occur when oxygen combines with a substance and energy is released (exothermic) General Form: C x H y + O 2  CO 2 + H 2 O Examples: C (s) + O 2 (g)  CO 2 (g) CH 4 + O 2  CO 2 + H 2 O

For each of the following, identify the type of reaction Fe + H 2 SO 4  Fe 2 (SO 4 ) 3 + H 2 C 2 H 6 + O 2  H 2 O + CO 2 Al + O 2  Al 2 O 3 KClO 3  KCl + O 2 KNO 3 + H 2 CO 3  K 2 CO 3 + HNO 3

Specific Rules for Reactions Decomposition –Metallic Carbonates, when heated, breakdown to form metallic oxides and carbon dioxide ZnCO 3 (s)  ZnO (s) + CO 2 (g)

Specific Rules for Reactions Decomposition –Many Metallic Hydroxides when heated, decompose into metallic oxides and water Mg(OH) 2 (s)  MgO(s) + H 2 O (g)

Specific Rules for Reactions Decomposition –Metallic chlorates, when heated, decompose into metallic chlorides and oxygen gas. KClO 3 (s)  KCl (s) + O 2 (g)

Specific Rules for Reactions Single Replacement Reaction –Replacement of hydrogen in acids by metals 2Al (s) + 6HCl (aq)  2AlCl 3 (aq) + 3H 2 (g)

Specific Rules for Reactions Single Replacement –Replacement of hydrogen in water by metals Fe (s) + 2H 2 O (l)  Fe(OH) 2 (s) + H 2 (g)

Specific Rules for Reactions Double Replacement Reaction –Neutralization Reaction is a type of chemical reaction that occurs between an acid and base to produce a salt and water. Ca(OH) 2 (aq) + 2HCl (aq)  CaCl 2 (aq) + 2H 2 O (l)