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# 11 17 How Are Equations Balanced

## on Nov 17, 2009

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## 11 17 How Are Equations BalancedPresentation Transcript

• Launch: 11/17   Grab your binder and immediately take a seat!   Place homework (practice questions) on desk. Mg + 2H2O  Mg(OH)2 + 2H2 3.  Is the above equation balanced? a.  No, because the number of H atoms is not equal b.  No, because the number of O atoms is not equal c.  Yes, because the number of Mg atoms is not equal d.  Yes, because there are equal numbers of atoms on both sides of the equation
• Launch 11/17 4.  Hydrogen gas (H2) and oxygen gas (O2) react to form water (H2O). Which of these represents a properly balanced equation for this reaction? a.  H2 + O2  H2O b.  2H2 + 2O2  2H2O c.  2H2 + O2  2H2O d.  H2 + 2O2  2H2O
• Announcements   Unit #5: Chemical Reactions & Stoichiometry   Class points end next week   Get your HW done   Be respectful   Quiz on Friday!
• How are equations balanced? Mr. Heffner 11/17/09
• Review   Is the below equation balanced? Cl2 + H2  2HCl 2 X Cl 2XH 2XH 2 X Cl Multiply the coefficients and subscripts Yes, it is balanced!
• How are equations balanced?   There is a 3-step process for balancing equations: 1.  Count the atoms on both sides 2.  Change a coefficient & multiply out 3.  Check tally (and repeat) Only one rule: you can’t change the subscripts
• Example #1   Balance the equation, H2 + O2  H2O
• Example #1   Step #1: Count the atoms on both sides H2 + O2  H2O 2XH 2XO 2XH 1XO Unbalanced!it underneath Put
• Example #1   Step #2: Change coefficient & multiply out H2 + O2  H2O 2 2XH 2XO ( 2XH 2X 1 X O ) 4XH 2XO
• Example #1   Step #3: Check tally (and repeat) 2H2 + O2  H2O 2 ( 2X 2 X H ) 2XO 4XH 2XO 4XH Still unbalanced!
• Example #1   Step #3: Check tally (and repeat) 2H2 + O2  H2O 2 4XH 2XO 4XH 2XO Balanced!
• Activity   Make the equation on your whiteboard   Balance the equation with the 3-step method 1.  Count the atoms 2.  Add a coefficient 3.  Check tally (and repeat)   Raise hand to get checked off   Record reactants, products, and final balanced equation on worksheet
• Practice Questions   Practice question handouts
• Exit Slip 1.  In a balanced equation a.  the reactant atoms are destroyed to make the products b.  the number of atoms on the reactants side of the equation is equal to the number of atoms on the products c.  the number of atoms on the reactants side of the equation is not equal to the number of atoms on the products d.  all compounds have a coefficient of at least 2
• Exit Slip H2 + Cl2  HCl 2.  Is the above equation balanced? a.  No, because H2 has a coefficient of 2. b.  No, because the number of Cl and H atoms are not equal. c.  Yes, because the number of H atoms is not equal on both sides. d.  Yes, because there are equal numbers of atoms on both sides of the equation.
• Exit Slip 4K + O2  2K2O 3.  In the already balanced reaction above, what is the coefficient for O2? a.  0 b.  1 c.  2 d.  4
• Exit Slip __C + __Br2  __CBr4 4.  When the equation above is completely balanced, the coefficient for Br2 would be a.  0 b.  1 c.  2 d.  4
• Exit Slip __Na + __H2O  __NaOH + __H2 5.  When the above equation is completely balanced, the coefficient for NaOH would be a.  1. b.  2. c.  4. d.  8.
• Homework   Finish practice question worksheet