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CHAPTER 7 Chemical Reactions: An Introduction

CHAPTER 7 Chemical Reactions: An Introduction. as expected, you will use this stuff ‘til the day you leave the class!. 7.1 Evidence for a Chemical Reaction. matter can combine or break apart to produce new kinds of matter w/ different properties = chemical reaction

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CHAPTER 7 Chemical Reactions: An Introduction

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  1. CHAPTER 7Chemical Reactions:An Introduction as expected, you will use this stuff ‘til the day you leave the class!

  2. 7.1 Evidence for a Chemical Reaction • matter can combine or break apart to produce new kinds of matter w/ different properties • = chemical reaction • how can you recognize one??? look for clues!

  3. Bubbles form(gas formation) – Alka-Seltzer in water, baking powder/soda in dough; some metals in acid • all give off gas= evidence of chm rxn! • dogs barking!! • more gas!!

  4. Color changes leaves, peeled apple, burned toast; all evidence of chemical rxncool video demo!!

  5. Appearance of a newsubstance(e.g. soap scum)

  6. Changes in heat and light – lit candle, burning charcoal, fuel oil on fire; • all give off heat/light= chm rxn • may take in heat or light(e.g. photosynthesis,baking soda in water) • cool demo!! • Another cool demo!!

  7. 7.2 Chemical Equations • hydrocarbons are a group of cmpds which release E in chm rxns; e.g.… • propane + oxygen  carbon dioxide + water + energyreactantsproducts • above is too long, so... • C3H8 + O2 CO2 + H2O + energy • this is a chemical equation

  8. Reversible rxns! • rarely is a rxnone way; oftenboth ways; e.g. • H2 + O2 H2O + energy but also… • H2O + energy  H2 + O2 so… • H2 + O2 H2O + energy

  9. law of conservation of mass = in a chemical rxn atoms are neither created nor destroyed • discovered by Antoine Laurent Lavoisier w/ experiments in a closed system What is it now!? What is it now?

  10. better way of stating it: all atoms are all accounted for in typical chm rxn • correct chm eq will obey LawConsMass! e.g. C + O2 CO2

  11. gotta make reactant and product masses equallookie here… H2 + O2 H2O • what is wrong? • all O’s not accounted for!how to fix? play w/ coefficients! 2H2 + O22H2O

  12. coefficients (the numbers in front) will show the proportion of the diff cmpds, e.g.: • 2H2 + O22H2O • 2 hydrogens : 1 oxygen (or) • 2 zillion hydrogens : 1 zillion oxygens (or) • 2 mol hydrogen : 1 mol oxygen

  13. 7.3 Balancing Chemical Reactions • when balancing, you may not mess w/ cmpd identities (formulae)!!! play only w/ coefficients! • make sure you have right chm formula first, • THEN balance using coefficients! • when counting, multiply atoms in cmpd by coeff • coefficients are whole numbers – make sure you use whole numbers!! make sure it is the simplest ratio!! so there! • Check this out!

  14. examples • C2H4 burns in oxygen to form carbon dioxide and water • C2H4 + O2 CO2 + H2O • C2H4 + 3O22CO2 + 2H2O • sodium and water react to form sodium hydroxide and hydrogen gas • Na + H2O  NaOH + H2 • 2Na + 2H2O 2NaOH + H2

  15. examples • magnesium nitride is formed from its elements • first, what is magnesium nitride? • Mg3N2 • Mg + N2 Mg3N2 • 3Mg + N2 Mg3N2

  16. examples • nitrogen monoxide gas reacts with hydrogen gas to form nitrogen gas and water • NO + H2 N2 + H2O • 2NO + 2H2 N2 + 2H2O

  17. examples • lithium metal reacts with chlorine gas to form solid lithium chloride • Li + Cl2 LiCl • 2Li + Cl22LiCl

  18. examples • diboron trioxide reacts with water to form boric acid, B(OH)3 • B2O3 + H2O  B(OH)3 • B2O3 + 3H2O 2B(OH)3

  19. examples • solid iron(III) oxide reacts with aqueous nitric acid to form aqueous iron(III) nitrate and water • Fe2O3 + HNO3 Fe(NO3)3 + H2O • Fe2O3 + 6HNO32Fe(NO3)3 + 3H2O

  20. examples • solid ammonium nitrite is heated to produce nitrogen gas and water vapor • NH4NO2 N2 + H2O • NH4NO2 N2 + 2H2O

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