Balancing Equations

1. Balancing Equations • Law of Conservation of Mass:

2. Balancing Equations • Paraphrase:

3. Balancing Equations • Balancing hints: • Balance the metals first. • Balance the ion groups next. • Balance the other atoms. • Save the non ion group oxygen and hydrogen until the end.

4. Balancing Equations Hydrogen + oxygen water H2 + O2 H2O • Hydrogen and oxygen are ________________. • Their subscripts ________________________ • The subscripts on _______________________

5. Balancing Equations H2 + O2 H2O • Count the atoms on each side.

6. Balancing Equations • H2 + O2 H2O • If the subscripts _______________, how can the atoms be made equal?

7. Balancing Equations H2 + O22H2O • H is no longer balanced!

8. Balancing Equations 2H2 + O22H2O • It’s Balanced!

9. Balancing Equations N2 + H2 NH3 Nitrogen + hydrogen ammonia • Count atoms.

10. Balancing Equations • Nothing is balanced. • Balance the nitrogen first by placing a coefficient of 2 in front of the NH3. N2 + H22NH3

11. Balancing Equations • Hydrogen is not balanced. • Place a 3 in front of H2. N2 + 3H22NH3

12. Balancing Equations Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 • Count atoms. • Reactants: Ca – 3 atoms, P – 2 atoms, O – 8 atoms; H – atoms, S – 1 atom, O – 4 atoms

13. Balancing Equations • Side note on Ca3(PO4)2 • The subscript after the phosphate indicates two phosphate groups. • This means two PO43- groups with two P and eight O atoms.

14. Balancing Equations • Ca3(PO4)2 + H2SO4CaSO4 + H3PO4 • Count atoms in the product.

15. Balancing Equations • In this equation: • Try to replace them with X and Y, like in the video. • Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4

16. Balancing Equations • Ca3(PO4)2 + H2SO4 CaSO4 + H3PO4 • Ca3X2+ H2YCaY+ H3X • Have a go!!

17. Balancing Equations Cu + H2SO4 CuSO4 + H2O + SO2 • The sulfate group breaks up. Each atom must be counted individually. Ugh!

18. Balancing Equations • Sulfur is not balanced. • Place a two in front of sulfuric acid. • Count atoms: 2 H2SO4 H – 4, S – 2, O - 8 • Cu + 2H2SO4 • CuSO4 + H2O + SO2

19. Balancing Equations • Hydrogen needs to be balanced so place a 2 in front of the H2O. • Count the number of atoms. • Cu + 2H2SO4 • CuSO4 + 2H2O + SO2

20. Balancing Equations • It’s balanced! • Cu + 2H2SO4 • CuSO4 + 2H2O + SO2

21. Word Problem • Copper (III) nitrate reacts with potassium hydroxide to form potassium nitrate and solid copper (II) hydroxide • Write the skeleton equation and balance it!

22. Balancing Equations • This method of balancing equations is the inspection method. • The method is trial and error. • Practice.

23. Practice Makes Perfect • Try #7a+b and #8 on pp. 117 • #9 for homework.

24. Lesson #10 – Types of Reactions • Synthesis • Decomposition • Combustion

25. Types of chemical reactions • http://www.youtube.com/watch?v=tE4668aarck&feature=related

26. Steps to Writing Reactions • Some steps for doing reactions • Identify the type of reaction • Predict the product(s) using the type of reaction as a model • Balance it Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as anelement. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

27. Synthesis reactions • _________________________________________________________________________________________________________________(Sometimes these are called combination or addition reactions.) __________________________________ • ____________________________________ • Example: 2H2 + O2  2H2O • Example: C+ O2  CO2

28. Synthesis Reactions

29. From your text: Synthesis Reactions involving compounds • Compounds – oxides and water. • When a ___________________ reacts with water, you get an acid. • Acids are composed of:

30. __________________________________________________________________________________________________________________________________________________________ Forms sulfur trioxide when it reacts with water. • Industrial plants burning fossil fuels

31. Metal Hydroxides ____________________________________________________________________________________________ • Ca + water = calcium hydroxide = lime • This can be added to contaminated lakes to counteract the effects of acid rain.

32. Sometimes you will have to give options……….. • Eg. Carbon and Oxygen can react to form either carbon monoxide or carbon dioxide. • If you only know the reactants, all you can do is give the options. • You would have to analyze the products of the reaction in the lab to be able to give a definite answer.

33. Practice • Predict the products. Write and balance the following synthesis reaction equations. • Sodium metal reacts with chlorine gas • Solid Magnesium reacts with fluorine gas • Aluminum metal reacts with fluorine gas

34. Decomposition Reactions • Decomposition reactions______________________________________________________________________________________________ • _________________________________ • In general: AB  A + B • Example: 2 H2O  2H2 + O2 • Example: 2 HgO  2Hg + O2

35. Decomposition Reactions

36. Decomposition Exceptions • Carbonates and chlorates are special case decomposition reactions that do not go to the elements. • Carbonates (CO32-) decompose to carbon dioxide and a metal oxide • Example: CaCO3  CO2 + CaO • Chlorates (ClO3-) decompose to oxygen gas and a metal chloride • Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2 • There are other special cases, but we will not explore those in Chemistry I

37. Practice • Predict the products. Then, write and balance the following decomposition reaction equations: • Solid Lead (IV) oxide decomposes • Aluminum nitride decomposes

38. Combustion Reactions • Combustion reaction: ________________________________________________________________________ • This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) _____________________2) _____________________3) _____________________

39. Combustion Reactions • In general: CxHy+ O2  CO2 + H2O • _______________________________________________________(although incomplete burning does cause some by-products like carbon monoxide) • Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

40. Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning. In the absence of enough oxygen, carbon containing compounds undergo incomplete combustion which results in carbon monoxide. Carbon monoxide is deadly!

41. Combustion • Example • C5H12 + O2 CO2 + H2O • Write the products and balance the following combustion reaction: • C10H22 + O2  8 5 6

42. Next week! • Lesson 11 & 13 • Wednesday we are in the same lab as before. • Make sure you have done all the readings and the self-checks • Practice, practice, practice!!! • The test is coming sooner than you think!!