Chemical Reactions
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  • 1. Chemical Reactions Chapter 11
  • 2. Using Everyday Equations Every minute of the day chemical reactions are taking place both in and around you. What makes something a chemical reaction? A chemical reaction involves one or more substances, the reactants, changing into one or more substances, the products. Reactants Products “ ” means “yields” or “reacts to produce.”
  • 3. Chemical reactions can be described many ways. One is by using a word equation. A word equation is an equation where reactants and products are represented by words. Example: methane + oxygen Word equations, while useful, are cumbersome. To better describe a reaction, writing the formulas is used. A chemical equation uses formulas of reactants (on the left) separated by an arrow from products (on the right). carbon dioxide + water
  • 4. Example: Fe + O 2 (Skeleton equation) - does not indicate the relative amounts of reactants and products Most often symbols are used to describe the state (i.e., gas, solid, etc.) of each substance Fe 2 O 3
  • 5. Balancing Chemical Reactions
    • Coefficients are small whole numbers that are placed in front of the formulas in an equation in order to balance it.
    • A chemical reaction is also described by a balanced equation in which each side of the equation has the same number of each element and mass is conserved.
  • 6. How do you write a balanced chemical equation?
    • 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.
    • What is the Law of Conservation of Mass?
  • 7. Practice
    • __ H 2 + ___ O 2  ___ H 2 O
    • __ SO 2 + ___ O 2  ___ SO 3
  • 8. Try to balance this reaction: __Al(OH) 3 (s) + __H 2 SO 4 (aq)  __Al 2 (SO 4 ) 3 (aq) + __H 2 O(l) Al S H O Al S H O 1 1 5 7 2 3 2 13 12 18 8 2 3 6 2 10 3 12 18
  • 9. Balance these equations
    • __ Mg + __ O 2 -> __ MgO
    • __ KClO 3 -> __ KCl + __ O 2
    • __ Cu + __ AgNO 3 -> __ Cu(NO 3 ) 2 + __ Ag
    • __KOH + __ H 3 PO 4 -> __ K 3 PO 4 + __ H 2 O
    •  
    • 2 Mg + O 2 -> 2 MgO
    • 2 KClO 3 -> 2 KCl + 3 O 2
    • Cu + 2 AgNO 3 -> Cu(NO 3 ) 2 + 2 Ag
    • 3 KOH + H 3 PO 4 -> K 3 PO 4 + 3 H 2 O
    • Even better…
    • 2 Mg (s) + O 2 (g) -> 2 MgO (s)
  • 10. Types of Reactions
    • There are five types of chemical reactions we will talk about:
      • Synthesis reactions
      • _____________ reactions
      • Single displacement reactions
      • ________________ reactions
      • Combustion reactions
    • You need to be able to identify the type of reaction and predict the product(s)
  • 11. Steps to Writing Reactions
    • Some steps for doing reactions
      • Identify the type of reaction
      • Predict the product(s) using the type of reaction as a model
      • Balance it
      • Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O 2 as an element.
      • In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!
  • 12. 1. Synthesis reactions
    • Synthesis reactions occur when two substances (generally elements ) combine and form a compound. (Sometimes these are called combination or addition reactions.)
    • reactant + reactant  1 product
    • Basically: A + B  AB
      • Example: 2H 2 + O 2  2H 2 O
      • Example: C + O 2  CO 2
  • 13. Practice
    • Predict the products. Write and balance the following synthesis reaction equations.
    • Sodium metal reacts with chlorine gas
    • Na (s) + Cl 2(g) 
    • Solid Magnesium reacts with fluorine gas
    • Mg (s) + F 2(g) 
    • Aluminum metal reacts with fluorine gas
    • Al (s) + F 2(g) 
  • 14. 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 H 2 O  2H 2 + O 2
    • Example: 2 HgO  2Hg + O 2
  • 15. Practice
    • Predict the products. Then, write and balance the following decomposition reaction equations:
    • Solid Lead (IV) oxide decomposes PbO 2(s) 
    • Aluminum nitride decomposes
    • AlN (s) 
  • 16. Practice
    • Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation:
    • N 2(g) + O 2(g) 
    • BaCO 3(s) 
    • Co (s) + S (s) 
    • NH 3(g) + H 2 CO 3(aq) 
    • NI 3(s) 
    (make Co be +3) Nitrogen monoxide
  • 17. 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  product + product
      • 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 H 2 O splits into ions, it splits into
    • H + and OH - (not H+ and O -2 !!)
  • 18.
    • We have looked at several reactions:
    • Fe + CuSO 4  Cu + Fe 2 (SO 4 ) 3
    • Li + H 2 O  LiOH + H 2
    • Such experiments reveal trends. The activity series ranks the relative reactivity of metals.
    • It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom.
    • Q: Which of these will react?
    • Fe + CuSO 4 
    • Ni + NaCl 
    • Li + ZnCO 3 
    • Al + CuCl 2 
    Cu + Fe 2 (SO 4 ) 3 NR (no reaction) Zn + Li 2 CO 3 Cu + AlCl 3 Yes, Fe is above Cu No, Ni is below Na Yes, Al is above Cu Cu Hg Ag Ca Mg Al Zn Fe Ni Sn Pb H Au Li Na K Yes, Li is above Zn
  • 19.
    • H is the only nonmetal listed. H 2 may be displaced from acids or can be given off when a metal reacts with H 2 O (producing H 2 + metal hydroxide). The reaction with H 2 O depends on metal reactivity & water temp.
    • Q: will Mg react with H 2 O?
    cold H 2 O hot H 2 O steam acid NR A: No for cold, yes if it is hot/steam Mg + H 2 O  H 2 + ZnCl 2 Complete these reactions: Al + H 2 O(steam)  Cu + H 2 O  Ca + H 2 SO 4  Na + H 2 O  H 2 + Mg(OH) 2 H 2 + Al(OH) 3 H 2 + CaSO 4 H 2 + NaOH Q: Zn + HCl  Cu Hg Ag Ca Mg Al Zn Fe Ni Sn Pb H Au Li Na K
  • 20.
    • All metals will have a specific place in the activity series. For simplicity, only the most common metals are shown.
    • The metals near the top of the activity series are more reactive because their valence electrons are more easily removed.
    • On tests and exams the activity series may appear as K, Na, … Ag, Au; you must remember that K is reactive, Au is not.
    • If the valence of a metal is not indicated in the question, use its most common valence (in bold on your periodic table) to determine the correct chemical formula.
    Other Activity Series Information
  • 21. Single Replacement Reactions
    • Write and balance the following single replacement reaction equation:
    • Zinc metal reacts with aqueous hydrochloric acid
    • Zn (s) + HCl (aq)  ZnCl 2 + H 2(g)
    • Note: Zinc replaces the hydrogen ion in the reaction
    2
  • 22. Single Replacement Reactions
    • Sodium chloride solid reacts with fluorine gas
    • NaCl (s) + F 2(g)  NaF (s) + Cl 2(g)
        • Note that fluorine replaces chlorine in the compound
    • Aluminum metal reacts with aqueous copper (II) nitrate
    • Al (s) + Cu(NO 3 ) 2(aq) 
    2 2
  • 23. 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  product + product
    • AB + CD  AD + CB
  • 24. Double Replacement Reactions
    • Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
    • Example:
    • AgNO 3(aq) + NaCl (s)  AgCl (s) + NaNO 3(aq)
    • Another example:
    • K 2 SO 4(aq) + Ba(NO 3 ) 2(aq)  KNO 3(aq) + BaSO 4(s)
    2
  • 25. Practice
    • Predict the products. Balance the equation
    • HCl (aq) + AgNO 3(aq) 
    • CaCl 2(aq) + Na 3 PO 4(aq) 
    • Pb(NO 3 ) 2(aq) + BaCl 2(aq) 
    • FeCl 3(aq) + NaOH (aq) 
    • H 2 SO 4(aq) + NaOH (aq) 
    • KOH (aq) + CuSO 4(aq) 
  • 26. 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 with 3) Something to ignite the reaction (spark)
  • 27. Combustion Reactions
    • In general: C x H y + O 2  CO 2 + H 2 O
    • 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 C 8 H 18 )
  • 28. Combustion
    • Example
      • C 5 H 12 + O 2  CO 2 + H 2 O
    • Write the products and balance the following combustion reaction:
      • C 10 H 22 + O 2 
    5 6 8
  • 29. Mixed Practice
    • State the type, predict the products, and balance the following reactions:
    • BaCl 2 + H 2 SO 4 
    • C 6 H 12 + O 2 
    • Zn + CuSO 4 
    • Cs + Br 2 
    • FeCO 3 