1. Balancing Chemical Equations
Why do you need to balance chemical equations? How do you do it?

2. Extra Credit Quiz 2 HCl + Ca(OH)2 → CaCl2 + 2 H2O
1. For the following equation:
a. Write an interpretation of the (chemical) statement in words
b. Identify each reactant and product as either a compound or an element
c. Draw a particulate model of the chemical reaction.
d. Perform an atom inventory
e. Is the equation “balanced?”
2 HCl + Ca(OH)2 → CaCl2 + 2 H2O

3. O2 + H2 = H2O
a. Write an interpretation of the (chemical) statement in words b. Identify each reactant and product as either a compound or an element c. Perform an atom inventory d. Draw a particulate model of the chemical reaction. e. According to the inventory and model, is the equation balanced?

4. CaCl2 (aq) + Na2SO4 (aq) -> CaSO4 (s) + 2NaCl (aq)
Is this an example of a chemical change? Why?

5. What does the law of conservation of matter state?

6. Balanced Equations What is a balanced equation?
Why do we need to balance equations?
N2 + H2 => NH3
Based on this unbalanced equation: for every 1 mole of nitrogen and hydrogen gas – how much poisonous ammonia gas is produced?
N2 + 3H2 => 2NH (for every 1 mole of nitrogen gas and 2 moles of hydrogen gas, 2 moles of poisonous gas is produced!)

7. Steps For Balancing Equations
1) Check the equation by completing an atom inventory 2) Begin to balance one atom at a time by changing/adding coefficients, so that amounts of each element are the same on both sides of equation *Do not change the identity of reactants or products, only the amount. (You can change H2O to 2H2O – but NOT H2O2) 3) Continue to adjust that atom amount (keeping it equal on both sides) until the final equation is balanced. *If water is in the equation, balance hydrogen and oxygen atoms last. *If you notice polyatomic ions (Ex: NO3), treat them as one unit, and do not try to balance each individual atom. 4) Rewrite the final balanced equation and recount all of the final atoms.

8. *If water is in the equation, balance hydrogen and oxygen atoms last.
*If you notice polyatomic ions (Ex: NO3), treat them as one unit, and do not try to balance each individual atom.
4) Rewrite the final balanced equation and recount all of the final atoms.

9. Example 1 : O2 + H2 = H2O
Balance the equation:

10. Example 2: CH4 (g) + Cl2 -> CHCl3 (l) + HCl(g)
This reaction shows how methane gas reacts with chlorine gas during wastewater treatment .
This reaction produces liquid chloroform and hydrogen chloride gas.
A wastewater treatment chemist would need to know how much chlorine to add and how much of the toxic gas HCl may be produced – so he or she would need a balanced equation.

11. CH4 (g) + Cl2 -> CHCl3 (l) + HCl(g)
Burning Methane: Is it balanced? If not, follow the steps to balance the equation.
CH4 (g) + Cl > CHCl3 (l) HCl(g)
Methane chlorine chloroform hydrogen gas chloride
Will the chemist know accurately how much toxic gas (HCl) is going to
be produced for each chlorine molecule she adds?

12. CH4 (g) + 3Cl2 -> CHCl3 (l) + 3 HCl (g)
- Balance Carbon/Hydrogen/Chlorine
- Equation is balanced (equal number of atoms in both reactants and products)
CH4 (g) + 3Cl2 -> CHCl3 (l) + 3 HCl (g)

13. For every molecule of methane burned – how much poisonous gas is produced?

14. Example 3: Al + Cl2  AlCl3 Is it balanced?

16. 1. Do an atom inventory for the following equation. 2. Is it balanced
1. Do an atom inventory for the following equation Is it balanced? Is there another way you could have found your answer?

17. Classwork: Due by NEXT FRIDAY 1/22
World of Chemistry Problems:
7.2 Review Problems 1a-c (Page 223)
7.3 Review Problems 1a-c , 2 , 4 , 5 (Page 232)