1. Conservation of mass Balancing Chemical equations

2. Law of conservation of mass
During chemical reactions,
THE MASS of the PRODUCTS are ALWAYS equal to THE MASS of the REACTANTS

3. Chemical equations
N2H4 + O2 N2 + 2H2O reactants products How does this equation show that mass is conserved during the combustion of hydrazine?
coefficient

7. Which has a greater mass?
Molar mass
Which has a greater mass?

8. MOLEs and Avogadro’s # MOLE = approx. 6.02 x 1023 particles of a
substance
What? Why?
It’s practical – just like a “dozen” of eggs or a “pair” of shoes
Chemical rxns almost always involve large numbers of particles
Because the math says so (at regular pressure and 0o C)

9. Molar mass For single elements- For compounds/molecules-
Molar mass = Atomic mass expressed in GRAMS
Oxygen (O) = 16.0 amu = 16.0 g
Carbon (C) = amu = g
For compounds/molecules-
Molar mass = SUM of its component atoms’ atomic
masses expressed in GRAMS
CO2 = g x 2(16.0 g) = g

10. Molar masses O2
H20
NaCl

11. Types of chemical reactions

12. Put on the safety glasses. Move to the back of the room.
Try not to be too astounded.
How do you know that a chemical reaction took place?
What type of chemical reaction took place?
How do you know it was that type of reaction?

13. All of these reactions produce CO2.
1) CaCO HCl CaCl2 + H2CO3
2) CaCO CaO + CO2
3) 2C2H O CO H2O
All of these reactions produce CO2.
Are they the same type of reaction?
NO!!
Double replacement
Decomposition
Combustion

14. SYNTHESIS = TWO OR MORE SUBSTANCES REACT TO FORM A SINGLE SUBSTANCE
Chemical reactions are defined by the way that reactants and products interact:
SYNTHESIS = TWO OR MORE SUBSTANCES
REACT TO FORM A SINGLE SUBSTANCE
General equation:
A + B AB
Examples:
2 Na + Cl NaCl
2 H2 + O H2O
The product of a synthesis is always a compound (more than one element)

15. Chemical reactions are defined by the way that reactants and products interact:
DECOMPOSITION = A single substance breaks into two or more simpler substances
General equation:
AB A + B
Examples:
CaCO CaO + CO2
2 H2O H2 + O2
A decomposition is the reverse reaction of a synthesis

16. Chemical reactions are defined by the way that reactants and products interact:
SINGLE REPLACEMENT = One element or substance takes the place of another element or substance in a compound
General equation:
A + BC B + AC
Examples:
Cu AgNO Ag + Cu(NO3)2
2 K H2O H KOH
Copper (Cu) takes the place of Silver (Ag) and Potassium (K) takes the place of one Hydrogen (H)

17. Chemical reactions are defined by the way that reactants and products interact:
DOUBLE REPLACEMENT = Two different compounds exchange positive ions and form two new compounds
General equation:
AB + CD AD + CB
Example:
Pb(NO3) KI PbI KNO3
Lead (Pb2+) and Potassium (K+) are the cations. There are one of each in both compounds.
There are still one of each in the new compounds, but bound to new anions.

18. COMBUSTION = A substance reacts with oxygen,
Chemical reactions are defined by the way that reactants and products interact:
COMBUSTION = A substance reacts with oxygen,
often producing CO2, H2O and heat (exothermic)
Examples:
CH O CO H2O
2 H2 + O H2O
CO2 and H2O are not ALWAYS both produced…unless an organic compound is combusting
Isn’t this a synthesis reaction?

19. Identifying chemical reactions
Explain why the formation of water can be classified as a synthesis reaction, or a combustion reaction.
Describe a single replacement reaction.