1. 14.1 Chemical Reactions
ANNE - 1: start at 7; 2: done; 3: start at 6; 4: done

2. Chemical Reactions
Chemical reaction: the process of breaking chemical bonds and reforming new bonds to make new substances

3. Evidence of Chemical Change
Four indicators of a chemical change:
1. Formation of new gas
2. Formation of new solid
3. Release energy (heat or light)
4. Color change
Coke and Chlorine
Iodine Clock Reaction
Chameleon Reaction

4. Reactants and Products
Reactant: starting substance(s)
Product: new substance(s) formed

5. Reaction Symbols
arrow = “to produce”
The small symbols in the parentheses (s, l, g, aq) indicate the phase of each substance in the reaction.
Symbol
Meaning
(s)
solid
(l)
liquid
(g)
gas
(aq)
aqueous - dissolved in solution

6. Law of Conservation of Mass
Mass cannot be created or destroyed, only rearranged.

7. Law of Conservation of Mass
Mass of reactants = mass of products

8. Example
5.0 g of magnesium (Mg) burns in 1.0 g of oxygen (O2). How many grams of magnesium oxide (MgO) should be produced?
Mg + O2  MgO
6 g

9. Check-In
10.2 g of Lithium Fluoride (LiF) and an unknown amount of sodium chloride (NaCl) react to form 13.5 g of Lithium chloride (LiCl) and 21.2 g of Sodium fluoride (NaF). How many grams of sodium chloride reacted?
LiF + NaCl  LiCl + NaF
24.5 g

10. A Reminder: Numbers in Chemical Formulas

11. Balancing Chemical Equations
The law of conservation of mass tells us that atoms and molecules must be balanced on both sides of a chemical equation.

12. Balancing Chemical Equations
coefficient
subscript
Rules:
Subscripts (small numbers) CANNOT be changed.
Coefficients (big numbers) placed in front of the chemical formula.
A coefficient applies to ALL atoms in the chemical formula.
Multiply coefficients by subscripts to get the total atoms.

13. Balancing Chemical Equations
coefficient
subscript
Write in pencil
So you can
Erase!!
Balancing Steps:
Draw a line to separate reactants from products
Make a list! – each element on each side
--Write in the same order
Add coefficients if needed (change your list!)

14. Balancing Chemical Equations
___Li2S + ___ Cl2 → ___ LiCl + ___S

15. Balancing Chemical Equations
___Mg + ___ O2 → ___ MgO

16. Balancing Chemical Equations Example #1
___Cu2S + ___ O2 → ___ Cu2O + ___ SO2

17. Balancing Chemical Equations Example #2
___ Al + ___ O2 → ___ Al2O3

18. Balancing Chemical Equations EXIT SLIP
___ CO2 + ___ H2 → ___ CH4 + ___ H2O

19. Hints for balancing:
Save single elements (Al, Cu, Na) and diatomic molecules (I2, Cl2, O2) for last.
C2H O2 → CO H2O

20. Hints for balancing:
Find Common Multiples
KClO3 → KCl O2

21. Hints for balancing: Keep polyatomic ions together
H2SO Ca3(PO4)2 → Ca(H2PO4) CaSO4