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Chapter 11

Chapter 11. Chemical Reactions. Writing Chemical Equations. Word Equations Names of reactants on the left of an arrow separated by plus signs Names of products to the right of the arrow separated by plus signs Ex: flour + water + yeast + salt  bread

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Chapter 11

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  1. Chapter 11 Chemical Reactions

  2. Writing Chemical Equations • Word Equations • Names of reactants on the left of an arrow separated by plus signs • Names of products to the right of the arrow separated by plus signs • Ex: flour + water + yeast + salt  bread - Ex: carbon + oxygen  carbon dioxide

  3. Word equation • Methane + Oxygen  Carbon dioxide + Water

  4. Chemical Reaction • When one or more substances (reactants) are changed into one or more new substances (products), a CHEMICAL REACTION has occurred • represented as a chemical equation Reactants  products

  5. If you mix two things together how do you know a chemical reaction has occurred?

  6. Evidence a reaction has occurred: • Color change • Gas released • Precipitate formed • Temperature change (endo or exothermic) • Odor produced • Smoke • Light • Flames • pH change • Flammable to nonflammable or vice versa

  7. Chemical Equations • Replaces words with chemical formulas skeleton equations- does not indicate the relative amounts of reactants and products- UNBALANCED • Here is the skeleton equation for rusting: • Fe + O2 Fe2O3

  8. Symbols for reactions • + separates 2 reactants or 2 products • (s) solid • (l) liquid • (g) gas • (aq) aqueous – solid dissolved in a liquid usually water • (c) crystal •  precipitate produced •  gas produced • Δ energy is needed •  yields or produces- separates reactants from products

  9. Symbols for reactions • A catalyst is a substance that speeds up the reaction but is not used up in the reaction • identified above the yield sign H2O2 H2 + O2 KMnO4

  10. Law of Conservation of Mass • Demo match • Silver nitrate

  11. Law of Conservation of Mass • Mass is never created or destroyed-ALL must be conserved and accounted for during a chemical reaction • The same number of atoms of reactant elements must equal the atoms of product elements • By balancing equations, we satisfy the Law of Conservation of Mass

  12. 11.1 Balancing Chemical Equations • A chemical reaction is also described by a balanced equation in which each side of the equation has the same number of atoms of each element and mass is conserved.

  13. 11.1 Balancing Chemical Equations • This is a balanced equation for making a bicycle. The numbers are called coefficients—small whole numbers that are placed in front of the formulas in an equation in order to balance it.

  14. 11.1 Balancing Chemical Equations • To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.

  15. Rules for balancing equations: • Write correct skeleton formula • Determine number of atoms of each element of reactants and products. COUNT POLYATOMIC ION AS A SINGLE UNIT if it appears unchanged on both sides of the equation • Balance elements one at a time by using coefficients-NEVER change subscripts • Begin with the easiest elements first • Check both sides to see if they match • Make sure coefficients are in the lowest possible ratio

  16. Remember diatomics!! • When you write the skeleton equation, remember these elements must be written as 2 atoms when they are not involved in a compound…. • Br2 I2 N2 Cl2 H2 O2 F2

  17. Types of Reactions

  18. Types of Chemical Reactions • Synthesis (combination) • Decomposition • Single Replacement • Double Replacement • Combustion

  19. 1. Synthesis • Synthesis (composition, combination) reaction • two or more substances react to form a single new substance. A + B  AB

  20. 1. Synthesis Rules for synthesis reactions • Element + element → binary compound • Metal + nonmetal → ionic compound • Nonmental + nonmetal → covalent compound • Compound + compound → ternary compound ex: CO2 + H2O → H2CO3

  21. Practice • Predict the products. Write and balance the following synthesis reaction equations. • Sodium metal reacts with chlorine gas Na(s) + Cl2(g)  • Solid Magnesium reacts with fluorine gas Mg(s) + F2(g)  • Aluminum metal reacts with fluorine gas Al(s) + F2(g) 

  22. 2. Decomposition reaction • a single compound breaks down into two or more simpler products. • AB  A + B

  23. 2. Decomposition Reactions Rules for Decomposition Reactions: • All binary compounds (ex: MgCl2) will break down into their elements • All carbonates (CO32-) break down into oxide and carbon dioxide • Chlorates (ClO3-) break down into binary salt and oxygen • Bases (OH group) and compounds with an H and an O will break down into water and an oxide

  24. Practice • Predict the products. Then, write and balance the following decomposition reaction equations: • Solid Lead (IV) oxide decomposes PbO2(s)  • Aluminum nitride decomposes AlN(s) 

  25. http://education-portal.com/academy/lesson/decomposition-and-synthesis-reactions.html#lessonhttp://education-portal.com/academy/lesson/decomposition-and-synthesis-reactions.html#lesson

  26. 3. Single Replacement – • one element replaces a second element in a compound. M + AB  MB + A N + AB  AN + B

  27. Activity Series Li K Ba Ca Na Mg Al Zn Fe Cd Ni Sn Pb H Cu Hg Ag Au lists metals in order of decreasing reactivity. As a general rule, more reactive metals replace less reactive metals in a compound

  28. 4. Combustion Reactions • Combustion reactions occur when a fuel reacts with oxygen gas, which produces heat! Fuel + O2 (+ Heat)  Product

  29. Combustion reactions • CxHy + O2 CO2 + H2O • Ex: C3H8(g) + 5O2 3CO2 + 4H2O + heat

  30. Hydrocarbon Combustion Reactions • Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) • Combustion is used to heat homes (CH4)and run automobiles (octane: C8H18)

  31. Carbon Monoxide Effects Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

  32. Combustion • Example • C5H12 + O2 CO2 + H2O • Write the products and balance the following combustion reaction: • C10H22 + O2  6 8 5

  33. 5. Double Replacement (precipitation) • Double replacement- also known as precipitation reaction, (and sometimes neutralization reaction) AB + CD  AD + CB • The attractive forces between t oppositely charged ions is greater than the forces of attraction between the water molecules and the ions

  34. 1. Double Replacement contColors of precipitants Precipitant formed Color Bright yellow Dark yellow Black Black Green White White White white • PbI2 • CdS • PbS • Ag2S • Ni(OH)2 • Al(OH)3 • PbSO4 • BaSO4 • Ca3(PO4)2 • AgCl

  35. Double Replacement Reactions • Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together • Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) • Another example: K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2

  36. Solubility rules

  37. Practice • Predict the products. Balance the equation • HCl(aq) + AgNO3(aq)  • CaCl2(aq) + Na3PO4(aq)  • Pb(NO3)2(aq) + BaCl2(aq)  • FeCl3(aq) + NaOH(aq)  • H2SO4(aq) + NaOH(aq) • KOH(aq) + CuSO4(aq) 

  38. Mixed Practice • State the type, predict the products, and balance the following reactions: • BaCl2 + H2SO4 • C6H12+ O2  • Zn + CuSO4  • Cs + Br2  • FeCO3

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