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Chapter 11

Chapter 11. Chemical Reactions. Recognizing Chemical Rxns (1). When a sub undergoes a chem change, it takes part in a chem rxn. After it reacts, it no longer has the same chem identity. Recognizing Chemical Rxns (2). A sub can undergo a chem change and become a different sub.

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Chapter 11

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  1. Chapter 11 Chemical Reactions

  2. Recognizing Chemical Rxns (1) • When a sub undergoes a chem change, it takes part in a chemrxn. • After it reacts, it no longer has the same chem identity.

  3. Recognizing Chemical Rxns (2) A sub can undergo a chem change and become a different sub. • chemrxns occur around you (e.g. rusting, bleaching) and inside your bodies (e.g. digestion, respiration) all the time.

  4. Evidences of chemRxn Many important clues indicate when chemrxns occur. • Light given out • Heat given out or absorbed • Sound come out • Change color

  5. Evidences of chemRxn (5) Precipitate form (6) Smoke come out (7) Bubbles (gas) formed (8) Explosion

  6. Evidences of chemical Changes

  7. Writing Chemical Eqns To describe any changes that take place • recognize what sub react and what sub form.

  8. Writing Chemical Eqns (1) • Reactant • A sub that undergoes a rxn. • Product • The new sub(s) formed. Reactant(s) product(s) A + B C + D

  9. Writing Chemical Eqns (2) • e.g. a familiar chemrxn involves the rxn between Fe and O2(reactants) that produces iron(III) oxide---- rust (product). Iron + oxygen → iron (III) oxide Translate into skeleton eqnby substituting with symbols and formulas. Fe +

  10. Word Eqns(1) Using words to describe a rxn • all the reactants and products, • with an arrow ‘ → ’ placed between them to represent change. • Reactants are placed to the left of the →, and • products are placed to the right.

  11. Word Eqns (2) • ‘+’ signs are used to separate reactants and also to separate products. Vinegar +baking soda sodium acetate + water+ carbon dioxide Write the word eqnfor ‘rusting’ of iron. Iron +

  12. Word Eqns (3) • Vinegar and baking soda are common names. • The cpd in vinegar that is involved in the rxn is acetic acid, and baking soda is NaHCO3. Acetic acid + sodium hydrogen carbonate → sodium acetate + water + carbon dioxide

  13. Chemical Eqns (1) To convert Word Eqns intochemeqns • Substitute the names of cpds and elements with chem formulas.

  14. Chemical Eqns (2) CH3COOH + NaHCO3 CH3COONa + H2O + CO2 Baking soda/ sodium hydrogen carbonate Vinegar/ Acetic acid

  15. Writing ChemEqns Potassium + chlorine potassium chloride K + Cl2 KCl

  16. Writing ChemEqns K + Cl2 → KCl

  17. Writing ChemEqns Aluminum + oxygen → aluminum oxide Write the skeleton eqn →

  18. Writing ChemEqns Al + O2 → Al2O3

  19. Writing ChemEqns Sodium hydroxide + hydrochloric acid→ sodium chloride + water →

  20. Writing ChemEqns NaOH + HCl → NaCl + H2O

  21. Writing Chemeqns Magnesium hydroxide + sulfuric acid → magnesium sulfate + dihydrogen monoxide →

  22. Writing Chemeqns Mg(OH)2 + H2SO4 → MgSO4 + H2O

  23. Writing Chemeqns Iron (III) chloride + sodium hydroxide → iron (III) hydroxide + sodium chloride FeCl3 + NaOH→ Fe(OH)3+ NaCl

  24. Writing Chemeqns Carbon disulfide + chlorine → carbon tetrachloride + disulfur dichloride CS2 + Cl2→CCl4+ S2Cl2

  25. Writing Chemeqns Sodium hydrogen carbonate → Sodium carbonate + carbon dioxide + water NaHCO3→ Na2CO3 + CO2 + H2O

  26. Writing Chemeqns Sodium hydroxide+ carbon dioxide → Sodium carbonate + dihydrogen monoxide NaOH + CO2→ Na2CO3 + H2O

  27. Chemical Eqns (3) • How to indicate the bubbles during this rxn are CO2? • How to indicate that precipitate formed at the bottom of a test tube?

  28. Chemical Eqns (5) CH3COOH(aq)+NaHCO3(s) →CH3COONa(aq)+H2O (l)+ CO2 (g)

  29. ChemEqns (5) CH3COOH(aq)+NaHCO3(s)CH3COONa(aq) +H2O(l) +CO2(g)

  30. Energy and ChemEqns (1) • Noticeable amts of energy are often released or absorbed during a chem rxn. • If energy is absorbed → endothermicrxn.

  31. Energy and ChemEqns (2) • e.g. the eqn for the rxn in which water breaks down into hydrogen and oxygen shows that energy must be added to the rxn.

  32. Energy and ChemEqns (3) • Rxns that release heat energy→exothermicrxns.

  33. Energy and ChemEqns (4) • a rxn that produces energy

  34. Energy and ChemEqns (5) • The word energy is not always written in the eqn. • It is used only if it is important to know whether energy is released or absorbed.

  35. Balancing ChemEqns (1) Law of conservation of mass • Matter is neither created nor destroyed during a chemrxn. Total mass reactant(s) = total mass product(s)

  36. Balancing ChemEqns (2) • In a chemrxn: • Atoms don’t change; • they just rearrange. • breaking of bonds of reactants → rearrangement of atoms→ new bonds (in products) • # and kinds of atoms in (reactants) = • those in the products. Law of conservation of atoms

  37. Balancing ChemEqns (3) • For a chemeqn to accurately represent a rxn, the same # of each kind of atom must be on the left side of the → as are on the right side. ■If an eqn follows the law of conservation of atoms → balanced.

  38. Balancing ChemEqns (4) • e.g. consider the eqn that represents breaking down carbonic acid into water and CO2.

  39. Balancing ChemEqns (6) • Examine the eqn for the formn of sodium carbonate and water from the rxn between sodium hydroxide and carbon dioxide.

  40. Balancing ChemEqns (7) • 1 C atom is on each side of the arrow, but the Na, O, and H atoms are not balanced.

  41. Balancing ChemEqns (8) • To indicate more than 1 unit taking part or being formed in a rxn, a # called a coefficient is placed in front of it to indicate how many units are involved. • a coefficient of 2 in front of the NaOH formula

  42. Balancing Chemical Eqns (9) • 2 Na atoms are on each side. How many O atoms are on each side? 4 on each side. • How about H atoms? • 2 on each side. • Because 1 C atom is still on each side, the entire eqn is balanced;

  43. Balancing an Eqn • The balanced eqn tells us that when NaOH and CO2 react, 2 units of NaOH react with each molecule of CO2 to form 1 unit of NaCO3 and 1 molecule of H2O.

  44. Major Classes of Rxns(1) 5 Major Categories 1.Combination/Synthesis Rxns 2. Decomposition Rxns 3. Single replacement/displacement Rxns 4. Double replacement/displacement Rxns 5. Combustion Rxns

  45. Reaction Types

  46. Combination Rxn • 1. Combination Rxn/ Synthesis Rxn • 2 or more reactants (elements or cpds) combine • →one single product (cpd). • e.g. Fe + S → FeS elements cpd R + S → RS

  47. A Synthesis Rxn • When Fe rusts, Fe metal and O gas combine to form 1 new sub, iron(III) oxide. more than 1 reactant but only 1 product.

  48. Combination Rxns Combination Reactions • a chem change in which 2 or more subs react to form a single new sub.

  49. Decomposition rxn • 2. Decomposition Rxn • 1 reactant (cpd) breaks down into 2 or more simpler subs (→ 2 or more products) • cpdbreak down into individual elements or simpler cpds 2HgO(s)→ 2Hg (l) + O2 (g) cpd Elements or cpds RS → R + S

  50. Decomposition Rxns Decomposition Rxns • a single cpd (reactant) breaks down into 2 or more simpler products.

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