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DO NOW

DO NOW. Pick up notes packet and two handouts Balancing Equations II is due tomorrow Read pages 280-288 for homework. CHEMICAL REACTIONS. Chemical Reactions.

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DO NOW

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  1. DO NOW • Pick up notes packet and two handouts • Balancing Equations II is due tomorrow • Read pages 280-288 for homework

  2. CHEMICAL REACTIONS

  3. Chemical Reactions • A chemical reaction is a process in which the physical and chemical properties of the original substances change as new substances with different chemical and physical properties are formed. • Remember: a new substance is always formed. • The properties and energies of the substances always change when a chemical reaction takes place.

  4. Characteristics A.There are always two kinds of substances: 1. Reactant - substance that enters into a chemical rxn 2. Product - substance produced by a chemical rxn. Reactants  Products

  5. Characteristics B.There is always a change in energy in a chemical rxn. Exothermic - energy is given off. (Something that is burning or gives off light) Endothermic - energy is absorbed. (Photosynthesis or test tube gets colder)

  6. Characteristics C.There is always activation energy Activation energy is the energy needed to form short-lived, highly energetic, extremely unstable, intermediate molecules that are rearranged to form products in the chemical rxn.

  7. Characteristics D.Bonding Capacity In order for a chemical rxn to occur, the reactants must have the ability to combine with substances to form products. Must follow the rules for bonding. Remember: An atom bonds with another atom to complete its outermost energy level.

  8. Characteristics E. Conservation of Mass Atoms can be neither created nor destroyed. The number of reactant atoms must equal the number of product atoms. This is important when balancing chemical equations.

  9. BALANCING CHEMICAL EQUATIONS Chemical reactions involve a rearrangement of atoms. Chemical equations are expressions in symbols and formulas that represent a chemical reaction. EXAMPLE: Magnesium + Oxygen yields Magnesium Oxide + energy (word equation) Mg + O2MgO + heat (skeleton equation) 2 Mg + O2 2 MgO + heat (balanced equation) A balanced chemical equation has the same number of atoms of each element on both sides of the equation.

  10. RULES TO FOLLOW • Change coefficients only. • Never change a symbol, formula, or subscript. • Place coefficients in front of the entire chemical formula.

  11. STEPS TO BALANCING AN EQUATION 1. Write the chemical equation for the reaction. • Verify that the chemical symbols and formulas are correct. 2. Count the number of atoms of each element on both sides of the arrow. • If the atom numbers are equal, then the equation is balanced. 3. Balance the equation using coefficients. A coefficient is a whole number placed in front of a chemical formula to indicate the number of molecules present. Balance metals, then nonmetals, then hydrogen, then oxygen • Look for the least common multiple (LCM). 4. Check your work by recounting the number of atoms on each side of the arrow.

  12. BALANCING EQUATIONS (Part One) 1. ______ Al + ______ O2 ______Al2O3 Al - O - Al - O -

  13. HOMEWORK The Balancing Equations II handout is homework. Due tomorrow. You are not required to show your work of counting atoms, but if you get the problem wrong and have not shown your work, I cannot give partial credit.

  14. DO NOW • Pick up handout • Get out notes and homework • Move to you lab desk and do the equation from Balancing Equation II handout assigned on the white board. Be thorough. You will present it to the class momentarily.

  15. Word Equations • Write the correct formulas for each of the chemicals named. Determine which are the reactant(s) and which are the product(s). • Write out the chemical equation for the reaction. • Count the number of atoms of each element on both sides of the arrow. • Balance the equation using coefficients • Check your work by recounting the number of atoms on each side of the arrow.

  16. Helpful Hints Symbols you should know: means “yields” (s)means solid Ag (s) (g) means gas H2 (g) (l) means liquid H2O (l) (aq) means aqueous NaCl(aq) dissolved in water

  17. Helpful Hints • All metals are singular • Non-noble gases are diatomic – travel in pairs. The diatomic gases are N2, O2, F2, Cl2, Br2, I2, H2

  18. HELPFUL HINTS Any word problem that you are converting to a balanced equation needs symbols if: • it is an acid (aq) • It is an ionic substance that you can tell its solubility by the rules (aq) or (s) • It explicitly states what it is • It is one of the seven diatomic gases (g) • A singular metal (s) or in the case of Hg (l)

  19. Practice 1. copper (II) hydroxide yields copper (II) oxide and water. 2. ammonia gas and hydrochloric acid yields ammonium chloride.

  20. Practice 3. potassium metal and water yields potassium hydroxide and hydrogen gas. 4. propane (C3H8) and oxygen yields carbon dioxide and water.

  21. HOMEWORK • Handout due Monday • Problem set, Chapter 9 #1-6 and #9-13 due Wednesday

  22. Types of Chemical Reactions • There are five basic types of chemical reactions. • Not all reactions will take these five forms. • Other classes of reactions will be considered later. • net ionic • oxidation-reduction • neutralization

  23. SYNTHESIS Reaction • sometimes called Combination • two or more simple substances combine to form a new, more complex substance. • What to look for: one product EX. 2 Mg(s)+ O2 (g) 2 MgO(s) 4 Fe(s)+ 3 O2 (g) 2 Fe2O3(s) metal corrosion due to oxidation

  24. SYNTHESIS Reaction

  25. DECOMPOSITION Reaction • a complex substance breaks down into two or more simpler substances. • What to look for: one reactant H2SO4 Ex. C12H22O11(s) 11 H2O(g) + 12 C(s) sucrose  water and carbon

  26. DECOMPOSITION Reaction

  27. COMBUSTION reaction • Also called an oxidation reaction • when compounds react with oxygen. • What to look for: a compound and oxygen (reactants) which should yield two compounds. EX. Hydrocarbon + O2 water + carbon dioxide CH4 (g)+ 2O2 (g)CO2 (g)+ 2H2O (g) 2 C4H10 (g)+ 13 O2 (g) 8 CO2 (g)+ 10 H2O (g)

  28. “COMBUSTION” reaction • According to your book, the examples below are called combustion reactions. We will call them SYNTHESIS. Metal + oxygen gas  metal oxide 4 Fe(s)+ 3 O2 (g) 2 Fe2O3 (s) Nonmetal + oxygen gas  nonmetal oxide 2 H2 (g) + O2 (g)2 H2O(l)

  29. SINGLE REPLACEMENT Rxn • Also called single displacement reaction • one element replaces another element in a compound. • Use the activity series of metals to determine if the metal can be replaced or not. • What to look for: uncombined elements on both sides of the arrow

  30. SINGLE REPLACEMENT Rxn

  31. ACTIVITY SERIES

  32. SINGLE REPLACEMENT A. An active metal will displace the metallic ion in a compound of a less active metal. Need to look at activity series. EX. Cu (s) + AgNO3 (aq) Cu(NO3) 2(aq) + Ag (s) B. Some active metals (all alkali metals and some alkaline earth metals) will react with water to produce a metallic hydroxide and hydrogen gas. EX. 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2 (g)

  33. SINGLE REPLACEMENT C. Some active metals, such as Al, Zn, and Fe, will displace the hydrogen in acids to give a salt and hydrogen gas. EX. Mg(s)+ 2 HCl(aq)MgCl2 (aq)+ H2 (g) D. Halogens(active nonmetals) will displace less active halogens. Fluorine is the most reactive, iodine is the least. EX. Cl2 (g)+ 2 NaBr(aq)2NaCl(aq)+ Br2 (g)

  34. DOUBLE REPLACEMENT Rxn • Also called double displacement reaction • different atoms in two different compounds replace each other. • two compounds react to form two new compounds – either a gas, precipitate, or water • What to look for: two compounds on each side Ex.HCl (aq)+ NaOH (aq)NaCl (aq)+ H2O(l) NaCl (aq)+ AgNO3(aq)2 NaNO3(aq)+ AgCl(s)

  35. DOUBLE REPLACEMENT Rxn

  36. PRACTICE 1. Br2 + NaINaBr + I2 2. SO3 + H2O H2SO4 3. Zn + HClZnCl2 + H2 4. Ga2O3Ga + O2 5. H2O2 H2O + O2 6. Ba(NO3) 2 + Na2SO4 BaSO4 + NaNO3 7. P2O5+ BaOBa3(PO4)2 8. C4H8 + O2 CO2 + H2O 9. PdCl2+ HNO3Pd(NO3)2 + HCl 10. C2H6 + O2 CO2 + H2O

  37. PRACTICE ANSWERS 1. Single replacement Br2+ NaINaBr + I2 2. Synthesis SO3+ H2O  H2SO4 3. Single replacement Zn + HCl ZnCl2 + H2 4. Decomposition Ga2O3Ga + O2 5. Decomposition H2O2 H2O + O2 6. Double replacement Ba(NO3) 2 + Na2SO4 BaSO4 + NaNO3 7. Synthesis P2O5+ BaO Ba3(PO4) 2 8. Combustion C4H8+ O2 CO2 + H2O 9. Double replacement PdCl2+ HNO3Pd(NO3)2 + HCl 10. Combustion C2H6+ O2 CO2 + H2O

  38. HOMEWORK • Work on Study Guide due Tuesday • Homework is to read pages 289-298

  39. DO THESE ON SCRAP PAPER • Pick up handout and get out homework. • Classify the following reactions: • 2 Ag + S  Ag2S • C4H8 + 6O2  4CO2 + 4H2O • 2K + 2H2O  2KOH + H2 • HCl + NaOH  H2O + NaCl

  40. AQUEOUS SOLUTIONS • A lot of reactions take place in water. • Whenever something is dissolved in water, it is called AQUEOUS. • There are a variety of solutes that can be dissolved in water. • Most chemical reactions involving aqueous solutions end up with a precipitate, gas, or water as one of the products. • In order to determine if a reaction will produce a precipitate, you must be familiar with the solubility rules.

  41. SOLUBILITY RULES • All common salts of the group 1A elements and ammonium are soluble. • All common acetates and nitrates are soluble. • All binary compounds of group 7A elements (other than F) with metals are soluble except those of silver, mercury (I), and lead. • All sulfates are soluble except those of barium, strontium, lead, calcium, silver, and mercury (I) • Except for those in rule 1, carbonates, hydroxides, oxides, sulfides, and phosphates are insoluble. • See a more complete table, page 974

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