1. When atoms bond, molecules are formed
ex: H2
If the molecule is formed of different atoms, its a compound
ex: H2O
Which symbol is written first in the formula:
+ or – oxidation number?

2. Interpreting Chemical Formulas
Subscript
the number of atoms of the preceding element
no subscript? 1 atom
changing a subscript changes the molecule H H O H O O H
H2O2

3. Interpreting Chemical Formulas
Coefficient
Number in front of a chemical formula
Tells the number of molecules
Example
3H20

4. You Try! 4CO2 How many molecules of carbon dioxide? 4
How many atoms of carbon per molecule ? 1
How many atoms of oxygen per molecule? 2
How many total carbon atoms?
How many total oxygen atoms? 8

5. Why the Coefficent? Respect the law of conservation of mass
Matter in = matter out
Ex: O + O2 -> O3
3 oxygen atoms in reactants
3 oxygen atoms in product
Use coefficients to balance matter in/out
Ex: 2H2 + O2 -> 2 H2O
4 atoms of H, 2 O in; same out

6. Reactants? Products? Ex: matter in matter out CH4 + 2O2 CO2 + 2H20
Note: it’s an arrow, not an equals sign!
Indicates the reactants are becoming the products
In some rxns the reverse is also true or

7. Use the RAP table C O O O C O O Lost H Created O NOT POSSIBLE!
CH O CO H20
REACTANTS
ATOMS
PRODUCTS 1
CARBON 4
HYDROGEN 2
OXYGEN 3
Lost H
Created O
NOT POSSIBLE!

8. Fe2 + Cl2 -> FeCl3 3 2 Reactants ≠ Products Needs Balancing R A P 2
(iron) 1
Cl (chlorine) 3
Reactants ≠ Products
Needs Balancing 2 6 6

10. PRACTICE ____ Fe + ____Br2  ____FeBr3
Balance the following:
____ Fe + ____Br2  ____FeBr3
____Ba + ____H2O  ____Ba(OH)2 + ____H2
____Fe2O3 + ____C  ____Fe + ____CO 2 3 2 2 3 2 3

12. Chemical reactions are accompanied by energy changes
Energy released
Some reactions liberate (release) energy
exergonic (exothermic)
‘liver lab’ rxn
Some require an input of energy
endergonic (endothermic)
photosynthesis
energy
time
Energy input
energy
time

13. Energy is required to start every reaction
This energy ‘hurdle’ is overcome by molecules called catalysts, who lower the amount of energy needed
enzymes are catalysts in cells
enzymes are catalysts in cells
energy
reaction time

14. Lactose glucose + galactose
example:
Lactose glucose + galactose
glucose
lactose
galactose2
lactase enzyme
Enzyme can be used over
Enzyme changes shape in response, facilitating change in bonds

15. H2O2 O2 + H20 Lab example: H2O2 water & O2 peroxidase enzyme
Enzyme can be used over
Enzyme changes shape in response, facilitating change in bonds

16. Animations http://www.kscience.co.uk/animations/anim_2.htm

17. Enzyme terms