Balancing equations

1,289 views

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,289
On SlideShare
0
From Embeds
0
Number of Embeds
29
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Balancing equations

  1. 1. You only get out what you put inWrite this title in your notebooks
  2. 2. Law of conservation of mass Matter is neither created nor destroyed – it is just changes form.For example, if you react hydrochloric acid with magnesium: 2HCl + 2Mg  H2+ 2MgClYou mix a liquid and a solid and get a gas a liquid – but nothing disappeared, it’s just different.Write the Law of Conservation of Mass in your notebook
  3. 3. Reaction equationsEquations are like the recipes you use to cookThey tell you what to put in – ReactantsAnd what you’ll get out – Products Write definitions of reactants and products in your notebook
  4. 4. Equations and balancingLook back at the equation on slide two.Copy the equation into your notebookCount the H, Mg, and Cl atoms in the Reactants and the Products.Reactants: _____ H, _____ Mg, _____ ClProducts: _____ H, _____ Mg, _____ Cl
  5. 5. Equations and balancingLook back at the equation on slide two.Copy the equation into your notebookCount the H, Mg, and Cl atoms in the Reactants and the Products.Reactants: __2__ H, __2__ Mg, __2__ ClProducts: __2__ H, ___2_ Mg, ___2_ Cl
  6. 6. There were the same number of atoms of each element in the products as the reactants You only get out what you put in.
  7. 7. Balancing equationsWhenever we write or use an equation in chemistry it MUST be balanced and obey the law of conservation of mass You only get out what you put in.
  8. 8. Balancing equationsSome equations are harder to balance than others, use the following technique and you’ll be fine.First write the equation BIG – so it goes all the way across the page.Balance this equation in your notebook as you watch a step by step demonstration.
  9. 9. ____Cu2O + ____C → ____Cu + ____CO2 Draw a line in front of each compound This is where you will write the Coefficient that tells you how many of each substance you have. Write a definition of Coefficient in your notebook.
  10. 10. ____Cu2O + ____C → ____Cu + ____CO2 Draw a line under the arrow so that you divide the area into two parts, Reactants and Products
  11. 11. ____Cu2O + ____C → ____Cu + ____CO2 Cu - Cu - O- O- C- C- List the elements on each side. List them in the same order
  12. 12. ____Cu2O + ____C → ____Cu + ____CO2 Cu - 2 Cu - O- 1 O- C- 1 C- Now count how many of each element there are on each side. I’ve done the Reactants – you do the Products.
  13. 13. ____Cu2O + ____C → ____Cu + ____CO2 Cu - 2 Cu - 1 O- 1 O- 2 C- 1 C- 1 Compare the numbers. Is it balanced? Are the same number of atoms going in as going out?
  14. 14. ____Cu2O + ____C → ____Cu + ____CO2 Cu - 2 Cu - 1 O- 1 O- 2 C- 1 C- 1 No there aren’t There are more copper atoms on the Reactant side than on the Product side. We need more copper on the Product side.
  15. 15. ____Cu2O + ____C → ____Cu + ____CO2 Cu - 2 Cu - 1 O- 1 O- 2 C- 1 C- 1 Important rule – we can only change the Coefficients – the number in front of the compound
  16. 16. ____Cu2O + ____C → __2_Cu + ____CO2 Cu - 2 Cu - 1 2 O- 1 O- 2 C- 1 C- 1 Now we have to update our element count. Look again – is the equation balanced?
  17. 17. ____Cu2O + ____C → __2_Cu + ____CO2 Cu - 2 Cu - 1 2 O- 1 O- 2 C- 1 C- 1 No it’s not. There is more Oxygen on the Product side than on the Reactant side.
  18. 18. __2_Cu2O + ____C → __2_Cu + ____CO2 Cu - 2 Cu - 1 2 O- 1 O- 2 C- 1 C- 1 We can only change the coefficients. So the only way to get more O on the reactant side is to add another Cu2O
  19. 19. __2_Cu2O + ____C → __2_Cu + ____CO2 Cu – 2 4 Cu - 1 2 O- 12 O- 2 C- 1 C- 1 Now we update our element count again. Look again – is the equation balanced?
  20. 20. __2_Cu2O + ____C → __2_Cu + ____CO2 Cu – 2 4 Cu - 1 2 O- 12 O- 2 C- 1 C- 1 No it’s not – there is more copper on the Reactant side than the product side.
  21. 21. __2_Cu2O + ____C → __4_Cu + ____CO2 Cu – 2 4 Cu - 1 2 O- 12 O- 2 C- 1 C- 1 We can only change the coefficients. Change the Cu to 4.
  22. 22. __2_Cu2O + ____C → __4_Cu + ____CO2 Cu – 2 4 Cu - 1 2 4 O- 12 O- 2 C- 1 C- 1 Now we update our element count again. Look again – is the equation balanced?
  23. 23. __2_Cu2O + ____C → __4_Cu + ____CO2 Cu – 2 4 Cu - 1 2 4 O- 12 O- 2 C- 1 C- 1 Yes! It is balanced. 2Cu2O + C  4Cu + CO2
  24. 24. PracticeNow it’s your turn.Follow the steps we just used and balance the following equations: 1. Write the equation big 2. Draw a line under the arrow 3. List the elements 4. Count the elements – is it balanced? 5. If not, change the Coefficients 6. Count again and repeat from step 4.
  25. 25. Practice 1/5 ___Na + ___Cl2  ___NaCl
  26. 26. Practice 2/5 ___H2 + ___O2  ___H2O
  27. 27. Practice 3/5 ___SnO2 + ___H2  ___Sn + ___H2O
  28. 28. Practice 4/5 ___NaCl + ___F2  ___NaF + ___Cl2
  29. 29. Practice 5/5 ___CH4 + ___O2  ___CO2 + ___H2O
  30. 30. Balancing polyatomicsDo you remember polyatomic ions?Ions that have more than one element in them  SO42+  NO3 -  OH-There’s a shortcut…
  31. 31. __H2SO4 +__Zn  __ZnSO4 + __H2 H-2 H-2 S- 1 S- 1 O- 4 O- 4 Zn - 1 Zn - 1 Instead of writing out all of the S and O separately, notice that SO4 is together on both sides.
  32. 32. __H2SO4 +__Zn  __ZnSO4 + __H2 H-2 H-2 SO4 - 1 SO4 - 1 Zn - 1 Zn - 1 We can count the SO4‘s instead.
  33. 33. Practice 1/2 __Al2(SO4)3 + __Ca(OH)2 → __Al(OH)3 + __CaSO4
  34. 34. Practice 2/2__AgNO3 + __K3PO4 → __Ag3PO4 + __KNO3
  35. 35. The end.

×