chem unit 1 pt 11

chemical equations

represent chemical reactions

1. arrows seperate the reactants from the products

2. “+” separates multiple reactants or products

reactants

starting materials

products

final materials

balancing chemical equations

the number of atoms among the products must be the same among the reactants

1. keep coefficients as simple as possible

systematic way to balance a reaction

1. restate the problem, the new statement of the problem is to find the missing coefficients: x, y, z

   1. ex. 1CH4 + xO2 —> yCO2 + zH2O

   2. the first coefficient “1” is chosen randomly

2. count all elements

   1. ex. count carbons (C) on both sides: y = 1

   2. count the next element, hydrogren: 4 = 2z

   3. count oxygen: 2x = 2y + z

chemists don’t like fractional coefficients, multiply the equation by the lowest common denominator if needed

states of matter

for reactants and products can be written in parentheses after each formula

1. (g) gas

2. (l) liquid

3. (s) solid

4. (aq) dissolved in aqueous (water) solution

molecular mass

the sum of the atomic masses of all atoms in a molecule

1. also called formula weight

ex. C6H12O6=

6(12 amu)+12(1 amu) + 6(16 amu)

= 180 amu

percent composition

the percentage of mass of a compound that comes from each of the elements in the compound

%element = (((number of atoms of the element)(atomic mass))/(molecular mass of the compound))*100

ex. C6H12O6 molecular mass is 180

%C = ((6×12 amu)/180 amu)*100 = 40%

%H = ((12×1 amu)/(180 amu))*100 = 6.7%

%O= ((6×16 amy)/(180 amu))*100 = 53.3%

mass(g)/molar mass(g/mol)

mole=

moles*Avogadro’s number

number of molecules=

mole

to express the amount of material/number of particles in a microscopic sample in a practical way, chemists use this unit

1. one ____ is the number of particles equal to the number of atoms in exactly 12g of C^12 (carbon-12)

carbon 12

atomic mass of this is exactly 12 amu

Na = 6.02×10²3

equation for Avogadro’s number

number of atoms in carbon 12

(number of molecules)*(molecular mass of H2O)

mass=

(number of pennies)*(value of a penny)

net worth=