1. balanced chemical reaction – same number of atoms of each element on either side of the arrow
reactants – are on left side of the arrow; stuff being consumed in reaction
products – are on right side of the arrow; stuff being formed in reaction
arrow, – means equals, or produces, or gives

2. combustion rxn – when something burns and consumes oxygen, O2

3. Inspect the unbalanced rxn for 10 sec
Balance reactions by adding coefficients to get the same number of each atom of each element on either side of the arrow
Balancing Hints
Inspect the unbalanced rxn for 10 sec
Leave the free, uncombined elements alone until the end
Work with pencil so you can erase mistakes
Practice lots of hw problems

4. formula weight (molecular weight) - sum of the atomic weights of all atoms in the species
Determine the MW of SCl2
Determine the MW of calcium nitrate

5. mass of element total mass species
Percent composition =
mass of element total mass species
x 100
Calculate the percentage composition of each element in chromium(III) oxide

6. mole – a quantity that contains 6.022 x 1023 particles
Avogadro’s #, N – 1 mole of anything = x 1023 particles

7. Amedeo Avogadro
Lorenzo Romano Amedeo Carlo Bernadette Avogadro di Quaregna e Cerreto

8. How many grams does 1 mole of lead, Pb weigh ?
molar mass – one mole (6.022 x 1023) of any substance is equal to the atomic weight of that substance (units are g/mole)

9. How many grams of Al are in 1 mole of Al atoms ?
g Al
What is the mass of a single Al atom ?
amu
What is the molar mass of Al ?
g/mole
I have g Al. How many atoms of Al do I have ?
6.022 x 1023 atoms Al

10. Which container has more atoms: 207.2 g Pb or 26.981538 g Al ?
same
How many atoms are in g Pb ?
6.022 x 1023 atoms Pb

11. Calculate the # moles in 4.558 g K

12. Calculate the # moles in 38.620 g H2O

13. Calculate the # grams in 3.97 moles CO2

14. Calculate the # molecules in 3.704 g H2O

15. Calculate the # of moles of carbon, C in 5.05 moles CO2

16. Calculate the # moles Cl- anions in 6.314 moles CaCl2

17. Calculate the # of hydrogen atoms in 14.5 g CH3OH

18. Empirical Formula’s in Calculations
empirical formula – formula containing the smallest, whole # ratio of atoms in a molecule
Empirical Formula’s in Calculations
Calculate the moles of each substance
Divide each moles by the smallest number to get the empirical formula

19. A compound was analyzed and found to contain 0. 789 g sulfur and 1
A compound was analyzed and found to contain g sulfur and g oxygen. What is the empirical formula of the compound ?

20. An oxide of gold, Au, is analyzed and found to be 89. 11% Au (by wt
An oxide of gold, Au, is analyzed and found to be 89.11% Au (by wt.) and 10.89% oxygen (by wt.). What is the empirical formula of compound ?
* assume 100 g sample

21. D2Q3 How and When to round during empirical formula calculations
≈ 2

22. Empirical formula vs. Molecular formula
Calculations always reveal empirical formula
Must be given the molecular weight, MW, to determine actual molecular formula
Ratio the actual MW vs. the MW of empirical formula

23. Is C2H3O the molecular formula ?
emp form
MW g/mole
C2H3O
Is C2H3O the molecular formula ?
Given: the molecular weight, MW for the actual compound is g/mole
129.1 g/mole g/mole
≈ 3
3(C2H3O)
C6H9O3
molecular formula

24. hydrates – salts with loosely held H2O’s of hydration
Na2SO4·7H2O
sodium sulfate heptahydrate
Mg(NO2)2 ·3H2O
magnesium nitrite trihydrate
CaCl2 exists as a hydrate g of hydrated calcium chloride was heated leaving g of dehydrated CaCl2. Determine:
the %water (by wt.) in the hydrated salt
the empirical formula of the hydrated salt

25. stoichiometry – a quantitative relationship between reactants and products via moles
How many moles of H2O are obtained from the combustion of 3.5 moles C3H8O ?

26. How many moles of O2 are required to completely combust 12
How many moles of O2 are required to completely combust 12.1 moles C3H8O ?

27. How many g of CO2 can be obtained by combusting 3.70 moles of C3H8O ?

28. Isopropyl alcohol, C3H8O was burned and 12. 5 g O2 was consumed
Isopropyl alcohol, C3H8O was burned and 12.5 g O2 was consumed. How many g H2O was produced ?

29. amount of product actually obtained theoretical yield of product
Limiting reagent – reactant that runs out first
Excess reagent – reactant left over after the rxn is finished
Theoretical yield – maximum obtainable product (based on the limiting reagent)
amount of product actually obtained theoretical yield of product
Percent yield =
x 100

30. 15. 0 g C3H8 was combusted with 15. 0 g O2
15.0 g C3H8 was combusted with 15.0 g O2. How many g of H2O are theoretically possible ?
Write the rxn and balance it
Calculate the theoretical yield starting with each reactant. The smallest value obtained is the theoretical yield and is thus the one based on the limiting reagent

31. 15. 0 g C3H8 was combusted with 15. 0 g O2 and 5. 84 g H2O is obtained
15.0 g C3H8 was combusted with 15.0 g O2 and 5.84 g H2O is obtained. What is the %yield of H2O ?