Chapter 2 – Scientific Laws in Chemistry
As chemists, we need a practical way to count atoms and molecules because chemical
processes happen between these particles. Because these particles are so small,
however, we cannot simply count in dozens or other small numbers. In order to simplify
counting and calculations with atoms, we work with moles. The videos of Chapter 2 will
help you learn to determine atomic mass and use atomic mass to convert number of
atoms to moles to mass and vice versa. These skills are essential to understanding the
stoichiometry of chemical reactions.
1. Calculate atomic mass of atoms from the mass and natural abundance of
isotopes
2. Convert between moles and number of atoms
3. Convert between mass and number (in moles)
4. Apply the mole concept to multi-step problems and conversions
Important Scientific Laws in Chemistry
1. Atomic theory grew out of different observations and laws:
A. Conservation of Mass
i. The amount of matter/mass in a chemical reaction stays constant
throughout the process; it is neither created nor destroyed
ii. “in a chemical reaction, matter is neither created nor destroyed”
1. If you can account for everything before and after a reaction, the
mass will be the same
iii. what happens to the gasoline we burn driving?
1. 2C8H18 + 25 O2 = 16 CO2 + 18 H2O
iv. Gasoline burns to form carbon dioxide and water
v. Total mass of the substances involved in a reaction does not change
vi. the atoms rearrange, but do not disappear. Mass is conserved
B. Conservation of Energy
i. Energy is neither created nor destroyed, though it can change forms.
Total energy stays constant.
C. Definite proportions and multiple proportions
i. Definite proportions
1. “All samples of a given compound, regardless of their source or how
they were prepared, have the same proportions of their constituent
