1. BCE Quiz Instructions: Put name, date period and title at the top of your paper. Number your paper 1 – 5 Leave 4 lines between each number Copy the equations, including the blanks. Use a different color to make dots for each atom Balance the equation and fill in the blanks with PENCIL

2. Copy and solve the following equations. Use dots to count atoms. 1)____ N 2 + ____ H 2  ____ NH 3 2)____ KClO 3  ____ KCl + ____ O 2 3)____ NaCl + ____ F 2  ____ NaF + ____ Cl 2 4)____ H 2 + ____ O 2  ____ H 2 O 5)____H 2 CO 3  ____H 2 O + ____CO 2 6)Bonus: Which of these do you think is the 2 nd reaction in the vinegar/soda experiment?

3. Balancing Chemical Equations with Coefficients and Subscripts A Tutorial by Robert D. McCall

4. Law of Conservation of Mass Matter can not be created or destroyed This means that in a chemical reaction, whatever you put in, you get out…no more and no less! In other words, the mass of the reactants will equal the mass of the products –Some of the product may be GAS and get away from you but it still exists

5. Balancing Chemical Equations: Subscripts H 2 OH 2 O 2 H 2 SO 4 Pb(OH) 2 ***Remember: It is not necessary to use a subscript for “1” --- the element symbol alone is enough

6. Balancing Chemical Equations: Coefficients 4H 2 OH 2 O 2 3H 2 SO 4 9Pb(OH) 2 ***Notice that there is also no coefficient “1”

7. Balancing Chemical Equations: Coefficients 4H2O4H2O When the coefficient is in front of the whole molecule, it means that many molecules. For instance, in the case above there are 4 water molecules H 2 O + H 2 O + H 2 O + H 2 O

8. Balancing Chemical Equations: Coefficients 3H 2 SO 4 The subscript “4” refers only to the oxygen atom When an atom has a coefficient AND a subscript, multiply to find out how many of that atom 3 x H 2 = 6 Hydrogens 3 x 1 Sulfur = 3 Sulfurs 3 x 4 Oxygens = 12 Oxygens 3H 2 SO 4 3H2SO43H2SO4 3H2SO43H2SO4

9. Balancing Chemical Equations: Coefficients 9Pb(OH) 2 A subscript OUTSIDE parantheses refers to all atoms inside the parantheses So that 2 means there are 2 O’s and 2 H’s. But don’t forget: everything gets multiplied by the coefficient, which in this case is 9. Count how many total atoms are in this group, then click to see the correct answer. 45 total atoms 9Pb(OH) 2 9 Pb 9 x 2 = 18 O 9 x 2 = 18 H

10. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  According to the Theory of Conservation of Matter, matter can ’ t be created or destroyed.  Every atom that goes INTO a chemical reaction (called the reactants) must be in the stuff that results from the chemical reaction (called the products)  When you have the same number of each kind of atom on both sides of the arrow, this is called a balanced equation.  All chemical equations MUST be balanced

11. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  To start balancing an equation, pick ONE element (in this case hydrogen or oxygen---I ’ ll go with hydrogen) and count all the atoms of it on each side of the arrow.  Note: the arrow represents the DIRECTION of the reaction  For each atom of the element you selected, draw a colored dot or a specific shaped dot (circle, square, triangle...as long as you use all the same shape for the same element) Click the space bar to count hydrogen atoms with dots.

12. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  Next, pick ANOTHER element (in this case oxygen is the only one left!) and count all the atoms of it one each side of the arrow. Click the space bar to count oxygen atoms with dots.

13. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  Notice that hydrogen is already balanced, but oxygen is not. There are three O’s on the left and only two on the right of the arrow. If you leave it like this it appears that you have created an oxygen atom out of nothingness…so, either this is not correct, or you are going to win the Nobel Prize for Chemistry this year!

14. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  If you guessed that you are not going to win the Nobel Prize for Chemistry this year, you are on the right track! Maybe next year…  In order to balance oxygen, you need to use coefficients. There are a couple of tips to keep in mind…

15. Balancing Chemical Equations: OH NO! It’s MATH! H 2 O + O 2  H 2 O 2  Tips for using coefficients:  Look for ODD numbers (like the 1 extra oxygen on the left side of this equation.)  Start by making the ODD numbers EVEN. How? Just multiply by 2!

16. Balancing Chemical Equations: OH NO! It’s MATH! ___ H 2 O + ___O 2  ___H 2 O 2 2  By placing a coefficient of 2 in front of H 2 O, you double the count of every atom in that molecule (Click to make it happen)

17. Balancing Chemical Equations: ___ H 2 O + ___O 2  ___H 2 O 2 2 “ But wait! ” you say. “ Now everything is out of balance! ” That ’ s okay, because even numbers are so easy to work with. No matter what you multiply them by, the product is always even!

18. Balancing Chemical Equations: ___ H 2 O + ___O 2  ___H 2 O 2 22  Start over. Now you have 4 hydrogens on the left, and only 2 on the right. EASY! Just put a coefficient of 2 in front of the H 2 O 2 and count again!

19. Balancing Chemical Equations: ___ H 2 O + ___O 2  ___H 2 O 2 22  Now the hydrogen is balanced, and look…  The oxygen is balanced, too…. 4 left, 4 right.  It doesn ’ t matter that the oxygen on the left is in 2 different molecules. That ’ s the whole point: matter got rearranged, but it ’ s all still there!

20. Balancing Chemical Equations: ___ H 2 O + ___O 2  ___H 2 O 2 22  Since everything is balanced, you know you only need 1 O 2 molecule for every 2 H 2 O molecules to make 2 molecules of H 2 O 2  Go ahead and put a “ 1 ” in front of O 2 to show that you know that. (Click!) 1

21. Balancing Chemical Equations: 2 H 2 O + O 2  2 H 2 O 2 _2_H 2 O + _1_O 2  _2_H 2 O 2 On a worksheet, write it like this, with a number in every coefficient blank: But when just writing equations in general, don ’ t use the number 1

22. Homework: Try these equations. Leave room to draw dots! 1)____ N 2 + ____ H 2  ____ NH 3 2)____ KClO 3  ____ KCl + ____ O 2 3)____ NaCl + ____ F 2  ____ NaF + ____ Cl 2 4)____ H 2 + ____ O 2  ____ H 2 O 5)____H 2 CO 3  ____H 2 O + ____CO 2 6)Bonus: Which of these do you think is the 2 nd reaction in the vinegar/soda experiment?