Review-Molecular Formula

1. Review-Molecular Formula • Nicotine, a component of tobacco, has an empirical formula of C5H7N. The molar mass of nicotine is 162 g. What is its molecular formula? • A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula.

2. Unit 10:Chemical Equations

3. Chapter Objectives • 1. To learn to write chemical equations • 2. To correctly interpret chemical equations

4. Chemical Reactions • In a chemical reaction, substances join together to form new substances • The original substances present are called REACTANTS • The new substances formed are called PRODUCTS

5. Discussion of Chemical Reactions • The general form of an equation is: • Reactants  Products • The  is read as “yields” or “reacts to produce”

6. Discussion of Chemical Reactions • A + B  C • Substance “A” and “B” react to produce substance “C”

7. Additional Symbols in Chemical Reactions • + used to separate reactants or products • (s) means chemical is in solid state • (l) means chemical is in liquid state

8. Additional Symbols in Chemical Reactions • (g) means chemical is in gas state • (aq) means chemical is dissolved in water • *See Table 10-1 in book (page 278)

9. Other Symbols •  means something is added to the reaction • Usually this is heat • Pt means a catalyst (Pt) is added

10. Skeleton Equations • Skeleton (Formula) Equation- the rough form of an equation • It only shows the framework for the chemical reaction

11. Write Skeleton Equations • Sodium metal reacts with Oxygen gas to form solid Sodium Oxide • Solid sulfur reacts with Fluorine gas to form gaseous Sulfur Hexafluoride when heated • Nitrogen reacts with Hydrogen to form Ammonia (NH3) gas. Heat is required.

12. Types of Reactions • There are five general types of reactions: • Synthesis • Decomposition • Single Displacement • Double Displacement • Combustion

13. Synthesis Reactions • Synthesis reactions are also called combination reactions • A synthesis reaction occurs when two substances combine to form a new compound

14. Synthesis Reaction Continued • The general form of a synthesis reaction is: • A + X AX • Substance “AX” is the only substance formed

15. Examples of Synthesis Reactions • 2 Mg (s) + O2 (g)  2 MgO (s) • Fe (s) + Cl2 (g)  FeCl2 (s) • U (s) + 3 F2 (g)  UF6 (g)

16. Decomposition Reaction • In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances

17. Decomposition Reactions Cont. • General Form of Decomposition Reaction: • AX A + X

18. Examples of Decomposition Reactions • 2 HgO (s)  2 Hg (l) + O2 (g) • Ca(OH)2  CaO (s) + H2O (g) • H2SO4 (aq)  SO3 (g) + H2O (l)  

19. Single Replacement Reaction • In a single replacement reaction (also called a displacement reaction), an element reacts with a compound • A + BX AX + B

20. Examples of Single Replacement Reactions • Mg + Zn(NO3)2  Mg(NO3)2 + Zn • Mg + 2 AgNO3  Mg(NO3)2 (aq) + 2 Ag

21. Rules for Single Replacement Reactions • Not all single replacement reactions occur • You can determine if a reaction will occur by knowing the activity series of metals

22. Rules for Single Replacement • The activity series tell you if one metal can replace another metal in a reaction • The Activity Series is ordered • Any metal that is above another metal in the activity series WILL REPLACE the less reactive metal

23. Li K Ca Na Mg Al Zn Fe Pb H* Cu Hg Ag Activity Series

24. Predict if the following reactions will occur • 1. Fe + H2O • 2. Mg + LiNO3 • 3. Na + AgCl

25. Double Displacement Reactions • In a double displacement reaction, two compounds react • The compounds swap elements with each other

26. Double Displacement Cont • Compounds contain a positive and negative part • In a double displacement, the positive parts swap places with each other as do the negative parts

27. Examples • PbCl2 (s) + Li2SO4 (aq)  PbSO4 (s) + 2 LiCl (aq) • ZnBr2 (aq) + 2 AgNO3 (aq)  Zn(NO3)2 (aq) + 2 AgBr (s)

28. Combustion Reactions • In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2) • The products are CO2 and H2O

29. Example • 2 C6H6 + 15 O212 CO2 + 6 H2O • *Combustion Reactions commonly require large coefficients

30. Ionic Equations • Most ionic compound dissociate (or break apart) when dissolved in water to form its component ions • For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)

31. Soluble Vs. Precipitate • Soluble means that the compound breaks down into its ions in water • Ex) NaCl is soluble so it forms Na+ and Cl- • Insoluble means that the compound doesn’t break down in water

32. Precipitate Reactions • In double replacement reactions, often one of the product will be insoluble • The insoluble product is referred to as a precipitate • Precipitate Rules are on the EOC sheet

33. Practice • Determine if soluble or insoluble: • A) NaCl B) K2O • C) Fe(NO3)3 D) AgCl • E) BaS F) Cd(OH)2 • G) FeCl3 H) PbCO3

34. Ionic Equations Continued • To write a Complete Ionic Equation: • Write the aqueous substances as ions (leave any substances in gas, liquids, & solids alone) • Example: • AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)

35. Writing Ionic Equations • 1. (NH4)2S (aq) + Cd(NO3)2 (aq)  NH4NO3 (???) + CdS (???) • 2. Zn(NO3)2 (aq) + (NH4)2S (aq)  ZnS (???) + NH4NO3 (???)

36. Spectator Ions • Spectator Ions-Ions that are not directly involved in a reaction • Spectator ions show up on both sides of the equation • Spectator Ions cancel out

37. NET Ionic Equations • Net Ionic Equation-Indicate the particles that actually take part in a reaction • The Net Ionic Equation does NOT include spectator ions • Net Ionic Equations must be balanced according to atoms and charge

38. Write Net Ionic Equations • 1. (NH4)2S (aq) + Cd(NO3)2 (aq)  • 2. Zn(NO3)2 (aq) + (NH4)2S (aq) 