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Describing a Chemical Reaction

Describing a Chemical Reaction. Indications of a Chemical Reaction Evolution of heat, light, and/or sound Production of a gas Formation of a precipitate Color change. ENERGY CHANGES IN REACTIONS : determined by CHANGES that occur IN chemical BONDING .

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Describing a Chemical Reaction

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  1. Describing a Chemical Reaction Indications of a Chemical Reaction • Evolution of heat, light, and/or sound • Production of a gas • Formation of a precipitate • Color change

  2. ENERGY CHANGES IN REACTIONS: determined by CHANGES that occur IN chemical BONDING. • Chemical reactions involve the BREAKING of chemicalBONDSin reactants and the FORMATIONof chemicalBONDSin products. • Example: In the combustion of propane, the bonds in propane and oxygen molecules are broken, while the bonds in carbon dioxide and water molecules are formed. • C3H8   +   5 O2  ——>  3 CO2   +   4H20  +   heat

  3. LAW OF CONSERVATION OF ENERGY • In an exothermic reaction, the chemical energy of the reactants is CONVERTED INTO HEATplus the chemical energy of the products. • In an endothermic reaction, HEATplus the chemical energy of the reactants IS CONVERTED into the chemical energy of the products. In both cases, the total amount ofENERGY BEFORE AND AFTERthe reactionIS THE SAME.

  4. Chemical Equations • Reactants – the substances that exist before a chemical change (or reaction) takes place. • Products – the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

  5. Word Equations • A WORD EQUATION describes chemical change using the names of the reactants and products. REMEMBER conservation of mass when converting to chemical equation Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactants Products

  6. TYPES OF CHEMICAL REACTIONS • 1. Oxidation-Reduction (gain/loss of electrons) • a. Synthesis – 2 or more substances form a new single substance • b. Decomposition – One substance breaks down into simpler substances • c. Single-displacement – A single element displaces another element from a compound • d. Combustion – A compound reacts with O2 to form H2O

  7. TYPES OF CHEMICAL REACTIONS 2. Double Displacement (reactions where two elements or groups of elements in two different compounds exchange places to form two new compounds) a. Precipitation – Two soluble substances form an insoluble precipitate b. Acid-Base – An acid reacts with a base to form a “salt” and water c. Gas Evolution – A gas is formed

  8. SYNTHESIS REACTION: two or more substances react to FORM A SINGLE SUBSTANCE. A + B → AB SO2 + O2 → SO3 CO + O2 → CO2 P4O10 + H2O → H3PO4 CuBr + Br2 → CuBr2

  9. DECOMPOSITION REACTION: a compound BREAKS DOWN into two or more simpler substances. AB → A + B H2CO3 → CO2 + H2O NCL3 → N2 + CL2 NaHCO3 → CO2 + Na2CO3 + H2O

  10. SINGLE-REPLACEMENT REACTION: one element TAKES THE PLACE of another element in a compound. A + BC → B + AC SiO2 + Mg → Si + MgO Cu + HgNO3 → Cu(NO3)2 + Hg Li + H2O → LiOH+ H2 H2SO4 + Ca → CaSO4 + H2

  11. COMBUSTION REACTION: a substance REACTS RAPIDLY WITH OXYGEN, often producing heat, light, CO2 and water (overlaps with other types). CH4 + O2 → CO2 + 2H2O C4H10 + O2 → CO2 + H2O C10H22 + O2 → CO2 + H2O CH4 + O2 → CO2 + H2O

  12. DOUBLE-REPLACEMENT REACTION: two different compounds EXCHANGE POSITIVE IONS and form TWO NEW COMPOUNDS. AB + CD → AD + CB CaCl2 + K3PO4 → Ca3(PO4)2 + KCl CaCO3 + HCl → H2CO3 + CaCl2 AgSO4 + NH4I → (NH4)2SO4 + AgI BaO + HNO3 → Ba(NO3)2 + H2O Al2(SO4)3 + Ca(OH)2 → Al(OH)3 + CaSO4

  13. Phase Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

  14. Phase Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction D 2 atm pressure 0 oC MnO2

  15. CH4 + 2 O2 CO2 + 2 H2OMatter/Mass Conserved Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms Timberlake, Chemistry 7th Edition, page 167

  16. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product. Coefficients are used to balance, NOT subscripts What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. H2 + Cl2 HCl

  17. Balancing Chemical Equations 1. Write a word equation for the reaction. 2. Write the chemical equation for all reactants and products, then use MINOH. 3. Balance metal coefficients first (M). 4. Next, look for polyatomic ions, and balance coefficients as a group (I). 4. Then, balance non-metal coefficients (N). 5. Balance O and H last (OH).

  18. Write a balanced equation for the reaction between iron (III) oxide and hydrogen to form iron and water 1) Write a word equation for the reaction. Iron (III) oxide + hydrogen  iron + water 2) Write the correct formulas for all reactants and products. Fe2O3 + H2 (g)  Fe + H2O 3) Determine the coefficients that make the equation balance. Fe2O3 + 3 H2 (g)  2 Fe + 3 H2O

  19. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide  bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl2 (g) + NaBr  Br2 (g) + NaCl 3) Determine the coefficients that make the equation balance. Cl2 (g) + 2 NaBr  Br2 (g) + 2 NaCl

  20. Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al2(SO4)3 + CaCl2 CaSO4 (s) + AlCl3 3) Determine the coefficients that make the equation balance. Al2(SO4)3 + 3 CaCl2 3 CaSO4 (s) + 2 AlCl3

  21. Ca Printable Version of Activity Series Activity Series Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Foiled again – Aluminum loses to Calcium Halogen Reactivity F2 Cl2 Br2 I2

  22. Write a balanced equation for the reaction between nitrogen trihydride and oxygen to form nitrogen monoxide and water. 1) Write a word equation for the reaction. Nitrogen trihydride + oxygen  nitrogen monoxide + water 2) Write the correct formulas for all reactants and products. NH3 + O2 (g)  NO + H2O 3) Determine the coefficients that make the equation balance. 4 NH3 + 5 O2 (g)  4 NO + 6 H2O

  23. Cl H H H Cl Cl Cl H reactants products reactants products H H Cl Cl Coefficients are used to balance, NOT subscripts H Cl Cl Cl H H H2 + Cl2 2 HCl (balanced) (unbalanced) H2 + Cl2 HCl 2 1 2 2 1 2 2 2

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