Chemical Reactions

1. Chemical Reactions

2. Evidence of a Chemical Reaction • Energy release (heat or light)

3. Evidence of a Chemical Reaction • Color change

4. Evidence of a Chemical Reaction • Odor • gas bubbles • smoke formation

5. Evidence of a Chemical Reaction • Precipitation

6. Representing Chemical Equations reactant 1 + reactant 2 → product 1 and product 2 produces Product(s) must be different than the reactants

7. Representing Chemical Equations Simply a “recipe” + + → Eggs and butter and flour produce a cake Word equations name the reactants and products. What is missing from this recipe? AMOUNTS!!!

8. Representing Chemical Equations • + → • Iron (II) and oxygen produce iron oxide • Fe (s) + O2 (g)→ FeO (s) • What is missing? • Amounts! • How do you figure out the amounts needed and produced?

9. Balancing Equations • Based on the Law of Conservation of Mass • “Matter is not created or destroyed in a reaction, just rearranged.” • Fe + O-O → Fe O • What is wrong here? • an oxygen atom is missing

10. Balancing Equations • Atom inventory Fe + O2→ Fe O • Reactant side Product side Fe O Fe O 1 2 1 1 Fe + O2→ Fe O Final equation:Fe + O2→ Fe O 2 2 2 2 2 2

11. Balancing Equations Steps: • 1. Write the skeleton equation (can’t escape formula writing) • 2. Count atoms in reactants • 3. Count atoms in products • 4. Change coefficients to make atom counts match. Never change subscripts. • 5. Reduce coefficients if necessary.

12. Practice Problems ____ AlBr3 + ____ K  ____ KBr + ____ Al ____ AlBr3 + 3 K 3 KBr + ____ Al ____ P4 + ____ Br2  ____ PBr3 ____ P4 + 6 Br2 4 PBr3

13. Symbols used in Equations + separates two reactants or two products → “Yields” separated reactants from products • Designates a reactant in the solid state • Designates a reactant in the liquid state (g) Designates a reactant in the gaseous state (aq) Designates a reactant in the aqueous state → → indicates that heat is supplied to a reaction → Indicates that a catalyst is used (here, platinum) heat Pt

14. Symbols used in Equations #1 separates two reactants or two products #2 “Yields” separated reactants from products #3 Designates a reactant in the solid state • Designates a reactant in the # 4 state (g) Designates a reactant in the # 5 state #6 Designates a reactant in the aqueous state # 7 indicates that heat is supplied to a reaction → Indicates that a # 8 is used (here, platinum) # 9 name the diatomic elements Pt

15. Classifying Chemical Reactions • Five general types • Synthesis one new product • Solid sodium and chlorine gas form solid sodium chloride 2Na(s) + Cl2(g) → 2NaCl(s) + → http://jchemed.chem.wisc.edu/jcesoft/cca/cca0/Movies/NACL1.html http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm

16. Classifying Chemical Reactions Combustion Must have O2 as a reactant 2 Mg + O2 → 2 MgO + → Combustion reactions are exothermic; energy is produced.

17. Classifying Chemical Reactions • Combustion of hydrocarbons (compounds containing hydrogen and carbon) • CH4(g) + 2O2(g)→CO2(g) + 2H2O(g) • Most fuels are hydrocarbons

18. Classifying Chemical Reactions • Decomposition Only one reactant • Hydrogen peroxide decomposes to release oxygen gas and leave water on your skin H2O2(aq)→ O2(g) + H2O(l) 2 H2O2(aq)→ O2(g) + 2 H2O(l)

19. Classifying Chemical Reactions • Single replacement reactionsOne reactant is an element • Copper reacts with silver nitrate to produce silver and copper nitrate. • Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq)

20. Single replacement reactions • Activity Series of Metals Lithium Iron Rubidium Nickel Potassium Tin Calcium Lead Sodium Copper Magnesium Silver Aluminum Platinum Manganese Gold Zinc Decreases Decreases

21. Single replacement reactions • Halogens Fluorine Chlorine Bromine Iodine Decreases

22. Classifying Chemical Reactions • Double replacement reactions both reactants are ionic compounds • A gas, liquid, or solid must be produced Silver nitrate and sodium chloride react to produce sodium nitrate and silver chloride AgNO3 (aq) + Na Cl (aq) → NaNO3 (aq)+ AgCl (s) Ag+ Cl- Na+ NO3- Na+ NO3- AgCl

23. Summary Reaction Classification

24. Reactions in Aqueous Solutions • Review: • Solution – homogeneous mixture • Solute – substance dissolved • Solvent – most plentiful substance in the solution • Water is the “universal solvent” • Other substances can also be solvents

25. Reactions in Aqueous Solutions • How does water dissolve ionic compounds? Water is a polar molecule. • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf http://programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.html

26. Reactions in Aqueous Solutions Reactions that form solids • Lead nitrate and potassium iodide • Two clear solutions – mix – precipitate forms Pb +2 NO3 - K+ I-

27. Reactions in Aqueous Solutions Reactions that form solids • What happened on an atomic level? • + → • Lead and iodide form a new compound • Nitrate and potassium are still dissolved ions – they did nothing but “watch” – spectator ions NO3 – Pb +2 K+ I- K+ NO3– PbI2

28. Reactions in Aqueous Solutions Reactions that form solids • Complete ionic equation • Pb +2 + NO3 - + K+ + I-→ PbI2 + NO3 - + K+ • Spectator ions • Net ionic equation • Pb +2 + I-→ PbI2

29. Reactions in Aqueous Solutions Reactions that form liquids • HBr (aq) + NaOH(aq)→ H2O (l) + NaBr(aq) Complete ionic equation .H+(aq) + Br-(aq) + Na+(aq) + OH -(aq)→ H2O(l) + Na+(aq) + Br-(aq) Net ionic equation H+(aq) + OH -(aq)→ H2O(l)

30. Reactions in Aqueous Solutions Reactions that form gases 2HI (aq) + Li2S (aq)→ H2S (g) + 2LiI (aq) Complete ionic equation 2H+ (aq) + 2I- (aq)+ 2Li+ (aq) + S2-(aq)→ H2S(g) + 2Li+(aq) + 2I-(aq) Net ionic equation 2H+ (aq) + S2-(aq)→ H2S(g)