Chemical Equations and Reactions

1. Chemical Equations and Reactions Chapter 8

2. Chemical Reactions • Def: process in which one or more substances are changed into new substances • Start w/ REACTANTS and make PRODUCTS • Law of Conservation of Mass – mass of reactants must = mass of products

3. Chemical Equations • Def: uses symbols and formulas to represent identities of molecular or molar amts of a rxn • 2H2(g) + O2(g)  2H2O(l)

4. Indications of Rxn • Evolution of heat and energy as light • Production of Gas (bubbles) • Formation of precipitate (insoluble compound) • Color change

5. Chemical Equations • Word Equations – gives names of reactants and products • Calcium + Oxygen  Calcium oxide

6. Chemical Equations • Formula Equations – use chemical symbols for the reactants and products • Word: Calcium + Oxygen  Calcium oxide • Formula: Ca + O2  CaO • Remember HONClBrIF – only for LONE element • Balance Charges when needed

7. Symbols

8. Symbols

9. Complete Chemical Eqn • BaCl2(aq) + Na2CrO4(aq)  BaCrO4(s) + 2NaCl(aq) • Formulas, Phases, Balanced • Ca(s) + O2(g)  CaO(s) (not balanced) • Solid sodium oxide is added to water and forms sodium hydroxide (dissolved in water).

10. Balancing Equations

11. Balancing Equations • Making a bicycle? • 4 major parts  • Frame + wheel + handlebar + pedal  bicycle • 1 Frame (F) 2 Wheels (W) • 1 Handlebar (H) 2 Pedals (P)

12. Balancing Equations • Bicycle = FW2HP2 • Equation: • F + W + H + P  FW2HP2 • Unbalanced  Balance it! • F + 2W + H + 2P  FW2HP2

13. Balancing Equations H2 + O2  H2O • Count # of atoms on each side of equation • Can only change COEFFICIENTS!! • Coefficients are in lowest whole # ratio • If can, treat polyatomic ions as one unit • If equation isn’t balancing… equation is WRONG!

14. Balancing Equations • FeCl2 + Na3PO4  NaCl + Fe3(PO4)2 • Al + O2  Al2O3

15. Types of Reactions

16. Types of Reactions • Synthesis (combination) • Decomposition • Single-Displacement • Double-Displacement • Combustion

17. 1. Synthesis Reactions • Two or more reactants form ONE product • A + X  AX • Elements w/ O2 or S to make oxides or sulfides • 2Ca + O2  2CaO • CO2 + H2O  H2CO3

18. 2. Decomposition Reactions • ONE compound broken down into two or more smaller parts • Reverse of combination • AX  A + X • Decomposition using electric  electrolysis • CaCO3 CaO + CO2

19. 3. Single-Displacement Rxns • A single element replaces another element in a compound • A + BX  AX + B • Y + BX  BY + X • BX and AX are generally IONIC compounds  A and B are elements

20. Activity Series • A MORE reactive metal will REPLACE a less reactive metal • Pg. 286 Activity Series • metals replace metals or H • nonmetals replace nonmetals • Cl2 + KI  ? • Zn + MgCl2  ?

21. 3. Single-Replacement Rxns • Mg + CuSO4 • Zn + H2O 

22. 4. Double-Replacement Rxns • Atoms or ions from two different compounds replace each other • AX + BY  AY + BX • X and Y “switch” • CaCO3 + 2HCl  CaCl2 + H2CO3 • HNO3 + Ca(OH)2 

23. 5. Combustion Rxns • Substance combines with O2 releasing large amts of heat and light • (C-H) Compound + O2 CO2 + H2O • Similar to combination rxn • CH4 + O2 

24. Predict the Products • MgSO4 + Na  • Synthesis of Aluminum oxide from its elements. • Combustion of ethane, C2H6 • Decomposition of calcium oxide to its elements

25. Reaction Rates

26. Rate-Influencing Factors • Collision Theory: reactions occur because of collisions between particles • Inc. rate of reaction = inc. collisions • Surface Area: • Temperature: • Concentration: • Catalyst: