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Unit 8 Chemical Reactions

Unit 8 Chemical Reactions. Textbook Chapter 8. Day 1: Review of Nomenclature (Pg.3 in notes). Law of Conservation of Mass Experiment.

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Unit 8 Chemical Reactions

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  1. Unit 8 Chemical Reactions Textbook Chapter 8

  2. Day 1: Review of Nomenclature (Pg.3 in notes)

  3. Law of Conservation of Mass Experiment Matter can neither be created nor destroyed. Therefore, the amount of mass I start with will always equal the amount of mass I get back in any chemical equation!

  4. 2NaOH (aq) + CuSO4 ---- Na2SO4(aq) + Cu(OH)2 (s) • Today we will be looking at the reaction of • NaOH with CuSO4. • NaOH and CuSO4 are moderately toxic. • Please be cautious when handling them!

  5. PreLab 1. 2S (s) + 3O2 (g)  2SO3 2. 2HCl + Mg  MgCl2 + H2 In the above reaction, 5.0g of HCl react with 2.0g Mg. 3.0g of MgCl2 are recovered, how many grams of H2 were lost? In the above reaction, 2.6g of S reacts with 2.0g O2. How many grams of SO3 are recovered?

  6. Data Table

  7. Homework page 5

  8. Day 2: Nomenclature Review • aluminum oxide ___________ • nitrogen trioxide ___________ • copper(II) nitrate ___________ • sodium carbonate ________ • lead(IV) oxide ________

  9. When 1 or morecompoundsare reacted to produce totally new compounds that havedifferentchemical and physicalpropertiesthan they did before. • A chemical reaction is represented by writing achemicalequation • Using chemical formulas, symbols, andcoefficients • An equation represents, the identities and relative amounts of what are called reactants and products in a chemical rxn • Reactants are the substances you start with in the reaction • Products are the results of the reaction CHEMICAL REACTIONS

  10. Subscript – # of atoms present results are called “products” Ingredients are called “reactants” 2H2 + O2 2H2O ANATOMY OF A CHEMICAL RXN Coefficient- How many of that molecule Reacts with “Yields” or produces

  11. To know for certain a chemical rxn has taken place requires evidence that 1 or more substances have changedidentity • Absolute proof of such a change can only be provided by chemically analyzingtheproducts. • However, certain observations can be made to provide qualitative indications of a successful chemical rxn. • Unexpected change INDICATIONS OF A CHEM RXN

  12. 1) Production of a gas • Seeing gas bubbles produced when 2 sub-stances are mixed is evidence of a reaction 2) Formation of a precipitate INDICATIONS OF A CHEM RXN • If a solid appears after 2 solns are mixed, the solid is called a precipitate

  13. 3) Color change • Change in color is often an indication of a chemical reaction INDICATIONS OF A CHEM RXN 4) Formation of heat and/or light • A release of energy as both heat & light is strong evidence of a chemical reaction

  14. SYMBOL EXPLANATION Separates Reactant from Reactant or Separates Product from Product + “Yields” Indicates Result Of Rxn Separates Reactants from Products (s) A reactant or product in the solid state; also used to indicate a precipitate Writing and Balancing Chemical Reactions: Common Symbols in Reactions There are other symbols that give scientists additional information about a reaction. • These symbols are used to indicate what kinds of reactants and products are involved, how they react, etc. SYMBOLS IN REACTIONS 

  15. SYMBOL EXPLANATION (l) A reactant or product in the pure liquid state (g) A reactant or product in the gaseous state (aq) A reactant or product in an aqueous solution (dissolved in water) SYMBOLS IN REACTIONS  Heat is added to the reaction A catalyst is added to the reaction cat

  16. SYMBOL MEANING A gas is produced A solid is produced SYMBOLS IN REACTIONS Common Substances in Chemical Reactions H2, N2,O2, F2,Cl2,Br2,I2 H2O NH3(Don’t confuse with ammonium, NH4+.)

  17. Key Words Used in Describing Chemical Reactions Words used to separate reactants from other reactants. • “Reacts with” • “Mixed together” • “Bubbled through”

  18. Key Words Used in Describing Chemical Reactions To separate reactants and products, you will generally see one of these words. *Yield *Combusted *Burned *Give *Produce *Form *Decompose

  19. Class Practice #1 Write the balanced chemical reaction for the following reaction. Be sure to include all appropriate symbols. When heated, solid tungsten metal reacts with oxygen gas to produce solid tungsten(VI) oxide.  W O2 WO3 +  (s) (g) (s)

  20. 2) Solutions of sodium iodide and lead(II) nitrate are mixed and form the precipitate, lead(II) iodide and aqueous sodium nitrate. + NaNO3 NaI Pb(NO3)2  PbI2 + (s) (aq) (aq) (aq)

  21. 3) When heated, solid aluminum oxide decomposes to form aluminum metal and oxygen gas. (g)  Al Al2O3 + O2 (s) (s)

  22. Homework page 8

  23. Day 3: Review…again (Page 9) • Cr2O3 ___________ • PO2 ___________ • AlCl3 ___________ • AgNO3 ___________ • S2O5 ___________

  24. Father of Modern Chemistry 1743 - 1794 Antoine Lavoisier First Described the “Law of Conservation of Mass”

  25. Antoine Lavoisier found that the mass of the reactants and the products are equal, even when the states of matter change. 0.7g Oxygen became a gas HgO Hg + O2 He started with: 10g of Mercury Oxide (HgO) He ended up with:and 9.3g Mercury… ...But what happened to the O2? 10 g. = 0.7 + 9.3 g. Matter is neither created nor destroyed.

  26. Conservation of atoms-the number of each type of atom on the reactants side of the chemical equation MUST be equal to the number of each type of atom on the products side of the equation. • Coefficient-represent the number of units of each substance taking part in the reaction • Balanced chemical equation-the same number of atoms of each element on both sides of the equation

  27. Four Steps to Balance Equations: • Set up your equation. • Count the number of atoms you have on both sides. 3. Balance by changing the coefficients and recounting. 4. Start the process again if it still does not balance.

  28. 10 N H H H2 N2 NH3 H N N H H Is this balanced? Why or Why Not? Let’s Count the Atoms: There are 2 nitrogen atoms There are 2 hydrogen atoms 1 nitrogen and 3 hydrogen…

  29. Atoms can only bond in certain ways…and its determined by their valence electrons N N N N N N N N N N N N H H H H H H H H H H H H H2 N2 H2 N2 H2 H2 That’s why we can’t change the subscripts. N2 H2 N2 N2

  30. H H H H H H Here is what it means... H2 2H2 I can’t live without you! When balancing equations,we can only change the coefficients! Subscripts - Small #’s below an element. Coefficients - Large #’s in front of the formulas.

  31. N H H H N N H H 13 Now, back to the balancing... H2 1 1 N2 NH3 1 We can only change coefficients before the symbols. 1 molecule of nitrogen 1 molecule of hydrogen 1 molecule of ammonia

  32. N2 + H2 NH3 Do both sides have the same amount of atoms? N H 1 2 2 3

  33. N2 + H2 NH3 N2 + 3 H22NH3 Do both sides have the same amount of atoms? 2 3 N H (2) 1 2 (6) (6) 2 3 Then it is a balanced equation.

  34. 1. Set up your equation. H2 + O2 H2O O H

  35. 2. Count the number of atoms you have of each on both sides. H2 + O2 H2O 1 2 O 2 H 2

  36. H2 + O2 H2O 1 2 O 2 H 2 3. Balance by changing the coefficients and recounting. 2 2 (2) Need to have at least 2 “O” (4) (4) But it changes the number of “H” How are you going to make “H” add up to 4? Is this balanced? Yes!

  37. Let’s try another: 2 Mg + HCl  H2 + MgCl2 1 Mg 1 2 (2) Cl 1 Need to have at least 2 “Cl” Is this balanced? Yes! 2 H 1 (2) Changing the Cl changes the “H”?

  38. Na + HCl NaCl + H2 1 Na 1 Cl 1 1 H 2 1 Let’s try another: 2 In this case, we will start with hydrogen since it is the only one unbalanced. (2)

  39. Na + HCl NaCl + H2 1 Na 1 Cl 1 1 H 2 1 But, changing the hydrogen in HCl affects the number of chlorine atoms. 2 2 (2) (2) (2)

  40. Na + 2HCl NaCl + H2 2 2 Changing the chlorine on the product side affects the sodium (Na) on the reactants side. So we must now change sodium as well. 1 (2) Na 1 (2) Cl (2) 1 (2) 1 H (2) 2 1

  41. Homework : Pg 10 and 11

  42. Day 4:Oxidation-Reduction ReactionsPage 12 (Synthesis, Decomposition and Single Replacement reactions. ) These are reactions in which electrons are transferred from one species to another. • In redox reactions the oxidation number for an element _________________ in a chemical reaction. • __________________ Number: A number assigned to an element, based on the distribution of electrons. The same element can have very different properties in different oxidation states. changes Oxidation

  43. Redox Reactions 0 0 -1 +1 +2 -1 +1

  44. Redox cont. +1 -1 +2(x1) +2 +4 (x 1) +4 -6 +6 (x1) +6 -8

  45. Oxidation is a reaction Reduction is a reaction in in which there is the which there is the gain of loss of electrons. electrons. 0 +1 0 -1 Ex: Na  Na+1 + e- Ex: Cl2 + 2e- 2Cl- “LEO the lion says GER” “OIL RIG” Losing of Electrons is Oxidation OR Oxidation Is Loss (of electrons) Gaining of Electrons is Reduction Reduction Is Gain (of electrons) Since oxidation is the loss of electrons and reduction is the gain of electrons, they must occur simultaneously. ** Any chemical process in which elements undergo changes in oxidation number is an oxidation – reduction reaction , or redox reaction for short.**

  46. Practice determining whether the following elements have been oxidized or reduced and label the reaction. 0 0 +3 -2 Fe 0 +3 Lose 3 oxidized O 0 -2 Gain 2 reduced Remember…“OIL RIG”

  47. 0 +1 -1 +2 -1 0 Mg 0 +2 lose 2 oxidized H +1 0 gain 1 reduced Cl -1 -1 neither neither Acid Base or Double replacement…not a Redox!!

  48. Now its YOUR TURN…. Homework!! Page 14

  49. Day 5: Types of Redox Reactions Page 15

  50. 1. Synthesis REACTION (also called Combination or Composition) • Synthesis means “_put together ” • 2 or more elements/simple compounds combine to form 1 compound. • General form: A +B  AB • Identifying feature: only one __product__

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