1. Section 2: Chemical Formulas and Equations Year 10 Science

2. The Language of Chemistry  Early chemists used symbols for elements and compounds derived from alchemy, a ‘mystical chemistry’. 2

3. The Language of Chemistry  Currently used symbols for the elements are those found on the Periodic Table.  Elements are represented by symbols, compounds by formulas and reactions by equations. 3

4. Formulas  Molecular(covalent) formulas are those made up of non-metals. They are listed on the data sheet of the booklet.  There are some flashcards on the website to help you learn them  Ionic formulas are those for metals joined to non-metals. You need to be able to write these given the ions on the data sheet.  There are activities in the booklet and the website to help you revise them. 4

5. The Language of Chemistry  In a chemical reaction, at least one new substance is formed.  Chemical equations are a shorthand way to represent long, complex reactions.  Chemical equations take the form: Reactants  Products 5

6. Conservation of mass Brainpop: Conservation of mass 6

7. Conservation of mass  The Law of conservation of mass states that matter can neither be destroyed or created. 7

8. Rearranging atoms  During chemical reaction the bonds in the reactants are broken. The atoms are rearranged and new bonds form. Reactants → Products A + B → C + D A → B + C A + B → C, etc.. 8

9. Some Common Reaction types  Precipitation  Decomposition  Combustion  Corrosion  Acid-base  Metal displacement.. 9 We will be studying Precipitation Some reactions of acids

10. Word Equations  Chemical reactions can be represented by word equations.  Photosynthesis can be represented as: Carbon dioxide + water  glucose + oxygen  Reactants: carbon dioxide, water  Products: glucose, oxygen 10

11. Experiment 2: Describing Chemical Reactions Remember to record:  What the reactants look like before the experiment  What the products look like at the end of the experiment. 11

12. A. Magnesium in hydrochloric acid How do we know that a chemical reaction has occurred? Describe this reaction using a word equation. 12

13. B. Copper sulfate + sodium hydroxide How do we know that a chemical reaction has occurred? Describe this reaction using a word equation. 13

14. C. Copper in silver nitrate solution How do we know that a chemical reaction has occurred? Describe this reaction using a word equation. 14

15. Word Equations  Complete the report for experiment 2.  Text: Read pages 88-89 and complete questions 1-7 page 89.  Exercise 4 page 11 booklet. 15

16. Text page 89 16

17. Chemical Equations  Brainpop: Chemical Equations Brainpop: Chemical Equations 17

18. Chemical Equations A chemical equation gives the chemical formulas of the reactants on the left of the arrow and the products on the right. Reactants  Products 18 C(s) O 2 (g) CO 2 (g)

19. Symbols Used in Equations Symbols used in chemical equations show:  -the states of the reactants.  -the states of the products.  -the reaction conditions. 19

20. Can you write a word equation for this reaction? What about the Law of Conservation of Mass?

21. Subscripts vs Coefficients  Subscripts tell you how many atoms of a particular element are in a substance. The coefficient tells you about the number of molecules or ion pairs of the substance.

22. Learning Check  How many oxygen atoms are present in: NaOH 3NaOH H2OH2O 2H 2 O 22 1 3 1 2

23. Learning Check How many oxygen atoms are present in: Cu(OH) 2 2 3Cu(OH) 2 6 2Na 3 PO 4 8 23

24. Chemical Equations are Balanced In a chemical reaction atoms are neither gained nor lost.  In a balanced chemical equation the number of reactant atoms is equal to the number of product atoms. 24

25. A Balanced Chemical Equation In a balanced chemical equation:  -there must be the same number of each type of atom on the reactant side and on the product side of a balanced equation.  -numbers called coefficients are used in front of one or more formulas. Al + S  Al 2 S 3 Not Balanced 2Al + 3S  Al 2 S 3 Balanced 25

26. Learning Check State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P 4 (s) + 6Br 2 (l)  4 PBr 3 (g)4 P 12 Br 12 Br B. 2Al(s) + Fe 2 O 3 (s)  2Fe(s) + Al 2 O 3 (s)2 Al 2 Fe 2 Fe 3 O3 O 26

27. Learning Check Decide if each equation is balanced or not. A. Na(s) + N 2 (g)  Na 3 N(s) No. 2 N on reactant side, 1 N on product side. 1 Na on reactant side, 3 Na on product side. B. C 2 H 4 (g) + H 2 O(l)  C 2 H 5 OH(l) Yes. 2 C = 2 C 6 H = 6 H 1 O = 1 O 27

28. Steps in Balancing an Equation To balance the following equation, Fe 3 O 4 (s) + H 2 (g)  Fe(s) + H 2 O(l)  Work on one element at a time.  Use only coefficients in front of formulas.  Do not change any subscripts. Fe:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + H 2 O(l) O:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g)  3Fe(s) + 4H 2 O(l) 28

29. Balancing Chemical Equations 1. Write the equation with the correct formulas. NH 3 (g) + O 2 (g)  NO(g) + H 2 O(g) 2. Determine if the equation is balanced. No, not all atoms are balanced. 3. Balance with coefficients in front of formulas. 4NH 3 (g) + 5O 2 (g)  4NO(g) + 6H 2 O(g) 4. Check that atoms of each element are equal in reactants and products. 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O)= 10 O(4 O + 6 O) 29

30. Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 4 3- as a single unit MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2 PO 4 3- = 2 PO 4 3- Balance Mg and Cl 3MgCl 2 (aq) + 2Na 3 PO 4 (aq)  6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 3 Mg 2+ = 3 Mg 2+ 6 Na + = 6 Na + 6 Cl - = 6 Cl - 30

31. Balancing Chemical Equations  When balancing equations you must follow a simple set of rules: 1. Atoms cannot appear from nowhere nor can they disappear. There must be the same number of each atom of each element on either side of the chemical equation. 31

32. Balancing Chemical Equations 2. You cannot change the small subscript numbers in a formula. 3. For example, H 2 O is water but H 2 O 2 is hydrogen peroxide, a type of bleach that would be incredibly dangerous to wash with or drink. 4. Change the subscript and you change the chemicals. 32

33. Balancing Chemical Equations You can only change the number in front of each chemical formula (the coefficient). For example, if you want to double the number of oxygen atoms in an equation, do not change O 2 into O 4. O 4 does not exist in that form and you just can’t go about creating things that don’t exist! Instead, write 2O 2. 33

34. Balancing Chemical Equations If you place a coefficient in front of a compound like Al 2 (CO 3 ) 3 then you have multiplied all the atoms in the formula by that number. For example: 2 Al 2 (CO 3 ) 3 contains: 2 X 2 = 4 Al atoms 2 X 1 X 3 = 6 C atoms 2 X 3 X 3 = 18 O atoms 34

35. Balancing Chemical Equations  Complete Exercise 6 page 12 booklet  Read page 90-91 text  Complete Q1-3 page 91 text  Now try:  Balancing equations worksheet in class files Balancing equations worksheet in class files 35

36. Text page 91 36

37. Online activities  Chembalancer Chembalancer  Creative chemistry Creative chemistry  It's elemental It's elemental  Tutorial 1 Tutorial 1  Tutorial 2 Tutorial 2 37

38. I want more… Chemistry!!! 38