1. Lecture: Chemical Change and Chemical Equations
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2. Mole song: https://www.youtube.com/watch?v=PvT51M0ek5c&spfreload=10

3. 1. Chemical reactions break bonds and form new bonds between atoms: ie fire, light, smell
2. Chemical rxns always produce a new substance w/ new
characteristic properties ?
3. In a closed system (?),
chemical rxns produce a change in energy, given off or taken in, but
energy cannot be created or destroyed: why?
Law of Conservation of Energy ? and
Law of Conservation of Mass ?

4. A. energy released is called exothermic:
ie: hot packs, flames, your metabolism (37 C)
Graph: note relationship of start/finish of line relative to the y-axis: energy:
Energy-Absorbing Reaction
Energy-Releasing Reaction
Products
Activation energy
Activation energy
Reactants
Reactants
Products
B. energy absorbed is called endothermic: ie ice packs
C. the energy required to start the reaction is called the
activation energy: ie scratching a match for a flame
Go to Section:

5. 4. Chemical equations
A. Law of Conservation of Mass:
in a closed system, all elements (and their mass) must be present,
and their # of atoms, be equal before and after the rxn:
(must be balanced)
-Counting Atoms:
NO3: (coefficient of 1)
N = 1, O = 3
2NO3: (coefficient of 2)
N = 2, O = 6
(NO3)3: (coefficient of ?)
N = 3, O = 9
2(NO3)4: (coefficient of ?)
N = 8, O = 24

6. formula mass for Na is = 22.99 amu (from periodic table)
-formula mass: sum of all the atoms’ mass in a chemical formula in units of amu (?):
formula mass for Na is = amu (from periodic table)
formula mass for H2O is:
one molecule: H2O H = 2 x 1amu = amu
O = 1 x 16amu = 16amu
formula mass = 18amu
two molecules: 2H2O H = 4 x 1amu = amu
O = 2 x 16amu = 32amu
formula mass = 36amu
three molecules: (H2O)3 H = 6 x 1amu = 6amu
O = 3 x 16amu = 48amu
formula mass = 54amu
coefficient

7. -Avogadro’s number is 6.02 x 10 23
it’s used in chemistry to show a
relationship between amu and grams
- mole: a substance with 6.02 x 1023 atoms (if an element) or molecules (if a compound)
so, a mole is a #,
like a dozen is a #:
what # does dozen mean?
what # does mole mean?
which is a stronger hydrochloric acid (HCl) and why:
2 molar HCl or 5 molar HCl ?

8. - mass of all the particles of a substance (ie: Na or water) which has
-molar mass:
- mass of all the particles of a substance (ie: Na or water) which has
one mole of particles (6.02 x 1023):
- measured unit is grams
- just change the amu unit to gram unit:
Na: amu =
22.99 grams in one mole
H2O: 18 amu =
18 grams in one mole
The water has the same # of particles as Na (mole),
and less mass
but more elements, why?

9. - calculating number of particles (atoms or molecules):
-use this formula:
Molar mass = sample mass
Avogadro’s # # particles
Example: How many particles (atoms) are of Na if:
- molar mass of Na = g (22.99 amu)
- sample size of Na = 12.9g
22.99 g = g
6.02 x ? # particles
? # particles x g = 6.02 x1023 x 12.9 g
? # particles = 6.02 x1023 x 12.9 g
22.99 g
? # particles = 3.39 x 1023

10. Example:
Solve for mass of the H2O sample if the:
- Molar mass = 18 g (H2 = 2 amu, O = 16 amu)
- # particles = 296 x 1050
18 g = ? mass.
6.02 x x 10 50
18 g x x = ? mass
6.02 x
18g x 296 x – 23
6.02
? mass = 8.9 x grams (sigfig?)

11. Balance equations intro video (6’ 44” Khan academy)

12. B. a chemical equation is written w/
reactants left and products right:
reactant + reactant  product
H + H + O  H2O
C. an arrow indicates a chemical rxn occurred:
a new substance is formed (product)
D. rules for balancing equations: due to L.C.M.
-subscripts tell the # of atoms,
-coefficients tell # “molecules”
-Subscripts do NOT change,
-only coefficients change!!!!!!!!!

13. -use only whole #’s (no fractions)
-do not split up compounds
-use the least # of atoms (coefficients: LCD)
-start w/ product side, then the simplest which is unbalanced
-use a pencil!!!!!!!
So, balance these equations using the rules:
2Mg + O2  MgO2
2Mg + 2O2  2MgO2
Br2 + KI  KBr2 + I2
2Br2 + 2KI  2KBr2 + I2

14. Zn + HCl  ZnCl2 + H
Zn + 2HCl  ZnCl2 + 2H
Fe + Cl2  FeCl3
2Fe +3 Cl2  2FeCl3
HCl + CaCO3  CaCl2 + CO2 + H2O
2HCl + CaCO3  CaCl2 + CO2 + H2O
H2 + N2  NH3
3H2 + N2  2NH3

15. Cl2 + KBr  Br2 + KCl
Cl2 + 2KBr  Br2 + 2KCl
CH4 + O2  CO2 + H2O
CH4 + 2O2  CO2 + 2H2O

16. Balance equations practice video:

17. 5. Chemical rxn rate/speed is due to # of atomic collisions, called:
collision theory (like cars colliding).
Based on these four factors:
A. concentration: increase particles per volume: more collisions
B. surface area: increase opportunity w/ greater surface: more collisions
C. temperature: increase energy thus activity: more collisions
D. catalysts: lowers activation energy, less energy needed to start rxns: more collisions

18. 6. Classifying chemical reactions, four categories:
A. synthesis: to put together, form bonds:
two or more substances combine to form one new substance:
A + B  AB :
C + O2  CO2
2Na + 2Cl2  2NaCl2
B. decomposition: to break down, break bonds:
complex substance breaks down into two simpler substances (opposite of synthesis):
AB  A + B:
H2O  H2 + O (Hydrolysis: splitting water)
H2CO3  H2O + CO2

19. C. single displacement: an uncombined element replaces an element which is part of a compound:
A + BC  AC + B:
Zn + 2HCl  ZnCl2 + H2
2Na + 2H2O  2NaOH + H2
D. double displacement: different elements in two different compounds replace each other:
AC + BD  AD + BC:
AgNO3 + KCl  KNO3 + AgCl
MgCO3 + 2HCl  MgCl2 + H2CO3

20. E. combustion:
also known as burning:
when oxygen combines w/ a substance (often a carbon compound) and
one of the products is a release of energy:
-light (light bulb?)
-heat (light bulb ?)
-sound (break sound barrier ?)