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Unit 8 - Chemical Reactions

Unit 8 - Chemical Reactions. Student Outcomes: I can give 5 indications that a chemical reaction has occurred.  I can use the activity series to predict the reactivity of chemical reactions. 

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Unit 8 - Chemical Reactions

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  1. Unit 8 - Chemical Reactions • Student Outcomes: • I can give 5 indications that a chemical reaction has occurred.  • I can use the activity series to predict the reactivity of chemical reactions.  • I can describe the five basic types of chemical reactions, including single displacement/replacement, double displacement/replacement, synthesis, decomposition, and combustion. • I can explain how to identify the type of chemical reactions. • I can balance chemical equations when given the reactants and products.  • I can predict products in chemical reactions.

  2. Indications that a chemical reaction has occurred: • Unexpected change in temperature (it gets hotter or colder but you did not intentionally add or remove heat) • Unexpected color change • Unexpected odor change • Unexpected solid formation (precipitate) or unexpected gas formation (bubbles)

  3. Watch these chemical reactions. Notice the evidence of a chemical reaction taking place. • https://www.youtube.com/watch?v=lJjfb2ydVzU

  4. Types of Reactions • There are five types of chemical reactions we will talk about: • Synthesis reactions • Decomposition reactions • Single displacement reactions • Double displacement reactions • Combustion reactions • You need to be able to identify the type of reaction and predict the product(s)

  5. Steps to Writing Reactions Main steps for doing reactions: • Identify the type of reaction • Predict the product(s) using the type of reaction as a model. • Use subscripts to write the compounds. • Use coefficients to balance the whole reaction so that there are the same number of each element on each side of the reaction equation.

  6. Don’t forget about the diatomic elements! (BrINClHOF) If any of these are NOT part of a compound, they must be diatomic. Bromine = Br2 Iodine = I2 Nitrogen = N2 Chlorine = Cl2 Hydrogen = H2 Oxygen = O2 Fluorine = F2 The word problem will simply state the namebut you will write the diatomic in the reaction. If it is part of a compound, do not add a suffix unless the criss-cross requires it. Example: magnesium oxide = MgO

  7. Indicators of state (these are written in italics and parenthesis after the reactants and products) • (s) = solid state • (l) = liquid state • (g) = gas state • (aq) = dissolved in water (aqueous) Note: Hg(l) means liquid mercury Hg+2(aq) or HgO(aq) means the mercury ions are dissolved in water.

  8. 1. Synthesis reactions • Synthesis reactions occur when two substances (usually elements) combine and form a compound. (Sometimes these are called “combination” or “addition” reactions.) reactant + reactant  1 product • Basically: A + B  AB • Example: 2H2 + O2  2H2O • Example: C+ O2  CO2

  9. Synthesis Reaction Example

  10. 1. Predict the products. (Criss-Cross for subscripts.) 2. Balance the reactions. (Use only coefficients.) • 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)  2Na(s) + Cl2(g) → 2NaCl Mg(s) + F2(g) → MgF2 2Al(s) + 3F2(g) → 2AlF3

  11. 2. Decomposition Reactions • Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds • 1 Reactant  Product + Product • In general: AB  A + B • Example: 2 H2O  2H2 + O2 • Example: 2 HgO  2Hg + O2

  12. Decomposition Reaction:

  13. Decomposition Exceptions • Carbonates and chlorates are special case decomposition reactions that do not go to the elements. • Carbonates (CO32-) decompose to carbon dioxide and a metal oxide • Example: CaCO3  CO2 + CaO • Chlorates (ClO3-) decompose to oxygen gas and a metal chloride • Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2 • There are other special cases, but we will not explore those in high school Chemistry.

  14. 1. Predict the products. (Criss-Cross for subscripts.) 2. Balance the reactions. (Use only coefficients.) • Solid Lead (IV) oxide decomposes PbO2(s)  • Aluminum nitride decomposes AlN(s)  PbO2(s) → Pb(s) + O2(g) 2AlN(s) → 2Al(s) + N2(g)

  15. Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N2(g) + O2(g) BaCO3(s)  Co(s)+ S(s)  NI3(s)  N2(g) + O2(g)→ 2NO (g) synthesis Nitrogen monoxide BaCO3(s) → CO2(g) + BaOdecomposition 2Co(s) + 3S(s)→ Co2S3 synthesis (use Cobalt (III) in product) 2NI3(s) → N2(g) + 3I2(g) decomposition

  16. 3. Single Replacement Reactions • Single Replacement Reactions occur when one element replaces another in a compound. • A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). • element + compound element + compound A + BC  AC + B (if A is a metal)OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H2O splits into ions, it splits into H+ and OH- (not H+ and O-2 !!)

  17. Single Replacement Reaction

  18. Single Replacement Reactions • Write and balance the following single replacement reaction equation: • Zinc metal reacts with aqueous hydrochloric acid (HCl) Zn(s) + HCl(aq) ZnCl2 + H2(g) Note: Zinc (cation) replaces the hydrogen (cation) in the reaction 2

  19. Single Replacement Reactions • Sodium chloride solid reacts with fluorine gas NaCl(s) + F2(g)  NaF(s) + Cl2(g) Note that fluorine (anion) replaces chlorine (anion) in the compound • Aluminum metal reacts with aqueous copper (II) nitrate Al(s)+ Cu(NO3)2(aq) Cu(s) + Al(NO3)3 2 2 2 3 3 2

  20. 4. Double Replacement Reactions • Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound • Compound + compound  compound+ compound • AB + CD  AD + CB

  21. Double Replacement Reactions • Think about it like trading square dance partners- cations are always paired with anions. • Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) • Pretend Ag and Na are guys partnered with different girls in the dance. Ag switches partners with Na. NO3 is a polyatomic, so it acts like one partner. Remember the Ag and Na are still written first in the products (not NO3Na).

  22. Double Replacement Reactions • Another example: K2SO4(aq) + Ba(NO3)2(aq)  2 KNO3(aq) + BaSO4(s) Pretend K and Ba are guys partnered with different girls in the dance. K switches partners with Ba. Both SO4 and NO3 are polyatomics, so they act like one partner each. Notice the subscripts are not the same on each side because they depend on the criss-cross of the compound itself and are not carried over to the other side of the equation.

  23. Predict the products by “trading partners.” Use subscripts to write the compounds. Use coefficients to 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)  See next slide for answers.

  24. Predict the products by “trading partners.” Use subscripts to write the compounds. Use coefficients to balance the equation. • HCl(aq) + AgNO3(aq)  HNO3 + AgCl • 3 CaCl2(aq) + 2 Na3PO4(aq)  Ca3(PO4)2 + 6 NaCl • Pb(NO3)2(aq) + BaCl2(aq)  PbCl2 +Ba(NO3)2 • FeCl3(aq) + 3 NaOH(aq)  Fe(OH)3 + 3 NaCl • H2SO4(aq) + 2 NaOH(aq)  2 H2O + Na2SO4 • 2 KOH(aq) + CuSO4(aq)  K2SO4 + Cu(OH)2

  25. 5. Combustion Reactions • Combustion reactions occur when a hydrocarbon reacts with oxygen gas. • This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)

  26. Combustion Reactions • In general: CxHy + O2  CO2 + H2O • 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 and run automobiles (octane, as in gasoline, is C8H18)

  27. Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

  28. Combustion • Example • C5H12 + O2 CO2 + H2O • Write the products and balance the following combustion reaction: • C10H22 + O2  8 5 6 20 CO2 + 22H2O 2 31

  29. Mixed Practice • State the type, predict the products, and balance the following reactions: • BaCl2 + H2SO4 • C6H12 + O2  • Zn + CuSO4  • Cs + Br2  • FeCO3  BaSO4 + 2 HCl 9 6 CO2 + 6 H2O ZnSO4 + Cu 2 CsBr 2 FeO + CO2

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