1. Chapter 3a Formulas, Equations and Moles Lecture Notes Dr. Sammia Shahid

2.  Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken  Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.  Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction Introduction

3.  The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction is:  C + O 2  CO 2  It contains the same information as the English sentence but has quantitative meaning as well.

4. Because of the principle of the conservation of matter conservation of matter an equation must be an equation must be balanced balanced It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 Chemical Equations

5. Balancing Chemical Equations A balanced chemical equation represents the conversion of the reactants to products such that the number of atoms of each element is conserved. reactants  products limestone  quicklime + gas Calcium carbonate  calcium oxide + carbon dioxide CaCO 3 (s)  CaO(s) + CO 2 (g)

6. Balancing Chemical Equations CaCO 3 (s)  CaO(s) + CO 2 (g) The letters in parentheses following each substance are called State Symbols (g) → gas(l) → liquid(s) → solid(aq) → aqueous

7. Balancing Chemical Equations A balanced equation MUST have the same number of atoms of each element on both sides of the equation. H 2 + O 2 → H 2 O Not Balanced H 2 + ½O 2 → H 2 O Balanced 2H 2 + O 2 → 2H 2 O Balanced

8. Balancing Chemical Equations The numbers multiplying chemical formulas in a chemical equation are called: Stoichiometric Coefficients (S.C.) 2H 2 + O 2 → 2H 2 O Balanced Here 2, 1, and 2 are stoichiometric coefficients.

9. Balancing Chemical Equations A balanced chemical equation shows that the law of conservation of mass is adhered to. In a balanced chemical equation, the numbers and kinds of atoms on both sides of the reaction arrow are identical. 2NaCl(s)2Na(s) + Cl 2 (g) right side: 2 Na 2 Cl left side: 2 Na 2 Cl

16. Balancing Chemical Equations 2.Find suitable coefficients—the numbers placed before formulas to indicate how many formula units of each substance are required to balance the equation. 2H 2 O(l)2H 2 (g) + O 2 (g) 1.Write the unbalanced equation using the correct chemical formula for each reactant and product. DO NOT TRY TO BALANCE IT YET! H 2 O(l)H 2 (g) + O 2 (g) DO NOT CHANGE THE FORMULAS!

17. Balancing Chemical Equations 3.Reduce the coefficients to their smallest whole- number values, if necessary, by dividing them all by a common denominator. 2H 2 O(l)2H 2 (g) + O 2 (g) 4H 2 O(l)4H 2 (g) + 2O 2 (g) divide all by 2

18. Balancing Chemical Equations 4.Check your answer by making sure that the numbers and kinds of atoms are the same on both sides of the equation. 2H 2 O(l)2H 2 (g) + O 2 (g) right side: 4 H 2 O left side: 4 H 2 O

19. Some of the Helpful Hints for balancing equations: Take one element at a time, working left to right except for H and O. Save O for next to last, and H until last. IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element) (Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units MINOH: try Metals first, then Ions, then Nonmetals, and Oxygen, then Hydrogen last Steps to Balancing Equations

20. Balancing Chemical Equations Do not change subscripts when you balance a chemical equation. You are only allowed to change the coefficients. H 2 O(l)H 2 (g) + O 2 (g) unbalanced 2H 2 O(l)2H 2 (g) + O 2 (g) Chemical equation changed! H2O2(l)H2O2(l)H 2 (g) + O 2 (g) Balanced properly

21. Balancing Chemical Equations Example 1: B 2 H 6 + O 2 → B 2 O 3 + H 2 O Balance O last B is already balanced Start by changing S.C. of H 2 O: B 2 H 6 + O 2 → B 2 O 3 + 3H 2 O

22. Balancing Chemical Equations Example 1: B 2 H 6 + O 2 → B 2 O 3 + 3H 2 O B and H are balanced Balance O by changing S.C. of O 2 B 2 H 6 + 3O 2 → B 2 O 3 + 3H 2 O BALANCED!

23. Balancing Chemical Equations Example 2:MnO 2 + KOH + O 2 → K 2 MnO 4 + H 2 O Balance O last Mn is already balanced Change S.C. of KOH to balance K MnO 2 + 2KOH + O 2 → K 2 MnO 4 + H 2 O

24. Balancing Chemical Equations Example 2:MnO 2 + 2KOH + O 2 → K 2 MnO 4 + H 2 O Mn, K, and H are balanced (H was balanced by chance) Balance O MnO 2 + 2KOH + ½O 2 → K 2 MnO 4 + H 2 O or 2MnO 2 + 4KOH + O 2 → 2K 2 MnO 4 + 2H 2 O

25. Balancing Chemical Equations Balance the following equations: –C 6 H 12 O 6 → C 2 H 6 O + CO 2 –Fe + O 2 → Fe 2 O 3 –NH 3 + Cl 2 → N 2 H 4 + NH 4 Cl

26. Balancing Chemical Equations Balance the following equations: –C 6 H 12 O 6 → C 2 H 6 O + CO 2 Unbalanced –C 6 H 12 O 6 → 2C 2 H 6 O + 2CO 2 Balanced

27. Balancing Chemical Equations Balance the following equations: –Fe + O 2 → Fe 2 O 3 Unbalanced –4Fe + 3O 2 → 2Fe 2 O 3 (balance O first)

28. Balancing Chemical Equations Balance the following equations: –NH 3 + Cl 2 → N 2 H 4 + NH 4 Cl Unbalanced –N:H is 1:3 on left, must get 1:3 on right! –4NH 3 + Cl 2 → N 2 H 4 + 2NH 4 Cl Balanced

36. The student will be able to:  describe and apply mass relationships in chemical reactions;  define and write chemical formulas;  write and balance chemical reactions and chemical equations. Learning Outcomes

37. DayTime Tuesday 09:00 am - 01:00 pm 03:00 pm - 04:00 pm Wednesday09:00 am - 11:00 am Thursday 09:00 am - 01:00 pm 03:00 pm - 04:00 pm Friday02:00 pm - 03:00 pm COUNSELING HOURS