Assume 100g sample

35.51g C

4.77 g H

37.85 g O

8.29 g N

13.60 g Na

x

x

x

x

x

1 mol C12.01g

1 mol H1.01g

1 mol O16.00g

1 mol N14.01g

1 mol Na22.99g

= 2.9567 mol

= 4.72277 mol

= 2.3656 mol

= 0.5917 mol

= 0.59156 mol

0.59156 mol

0.59156 mol

0.59156 mol

0.59156 mol

0.59156 mol

= 4.99

= 7.98

= 3.99

= 1.00

= 1.00

= 5

= 8

= 4

= 1

= 1

Empirical formula C5H8O4NNa

Molar mass of empirical formula - 169.13 g/mol

Therefore the empirical formula = molecular formula = C5H8O4NNa

HW answers: pg 110

13. 3.07 x 1024 atoms S

14. 9.97 x 10-15 mol Co

19. 3.44 x 10-10 g Pb

25. 409 g/mol

26. 6.69 x 1021 molecules C2H6

42. a. 46.65% N

b. 35.00% N

c. 71.13% N

d. 82.27% N

43. Empirical=molecular = C6H10S2O

48. 5.96 g F

50. a. CH2O

b. KCN

53. C8H10N4O2

CHEMICAL REACTIONS AND STOICHIOMETRY

Sections 3.7-3.8

How many toy tractor trailers can you make from the following?

350 tires1125 truck frames87 seats15 steering wheels

What additional information would you need to answer this problem?

Describing Chemical Reactions

A chemical reaction is the process by which one or more substances are changed into one or more different substances

(NH4)2Cr2O7(s) N2(g) + Cr2O3(s) + 4H2O(g)

“The reactant ammonium dichromate yields the products nitrogen, chromium (III) oxide and water vapor”

reactants

products

6

(NH4)2Cr2O7(s) N2(g) + Cr2O3(s) + 4H2O(g)

A CHEMICAL EQUATION represents, with symbols and formulas, the identifies and relative amounts of the reactants and products in a chemical equation

The physical state of the substance is placed after the formula as a subscript in parentheses.

(s) – solid

(g) – gas

(l) – liquid

(aq) – aqueous (dissolved in water)

Symbol Explanation

+ Separates two or more reactants or products

Yields - separates reactants from products

→ Reversible reaction

(s); (l); (g) solid, liquid or gas

(aq) Aqueous solution – a substance dissolved in water

Heat supplied

Platinum used as a catalyst

heat→

→Pt

Δ→

Chemical Equations

Sulfur burns in oxygen to produce sulfur dioxide gas.

S(s) + O2(g)

When solid potassium is added to water, hydrogen gas and aqueous potassium hydroxide are produced

K(s) + H2O(l)

Heat SO2(g)

H2(g) + KOH(aq)

Indications of a Chemical Reaction1. Evolution of heat and light is strong

evidence that a chemical reaction has taken place! But, the evolution of heat or light by itself is not necessarily a sign of a chemical change since

many physical changes also release either heat or light. 2. Production of gas! (aka bubbles when two

substances are mixed)

3. Formation of precipitate! A solid that is produced as a result of a chemical reaction in solution and that separates from the solution is known as a precipitate

4. Color Change!

Characteristics of Chemical Equations

1. The equation must represent all reactants and products.

2. The equation must contain the correct formulas for the reactants and products

3. The law of conservation of mass MUST be satisfied!!

Law of conservation of mass – atoms are neither created nor destroyed in ordinary chemical reactions

To equalized numbers of atoms, coefficients are added in front of the formulas where necessary

11

Formation of Water

Water is formed from oxygen gas and hydrogen gas.

Using the atoms, form both reactants. Using only the atoms of the reactants, form the product. No atom of reactant can be left over. No more atoms can be taken from the box.

(Hint: You may need more than one of the reactants/products in order for all atoms to be used in the products)

Practice Satisfying the Law of Conservation of Mass

Balancing Chemical Reactions

___H2 + ___Cl2 ___HCl

___ H2O ___ H2 + ___ O2

___ Mg + ___ HCl ___ MgCl2 + ___ H2

___ CaO + ___ SO2 ___ CaSO3

___ H2SO3 + ___ O2 ___ H2SO4

Practice Satisfying the Law of Conservation of Mass

Balancing Chemical Reactions

___ Na + ___ F2 ___ NaF

___ Na + ___ H2O ___ NaOH + ___ H2

___ KClO3 ___ KCl + ___ O2

___ C3H8 + ___ O2 ___ CO2 + ___ H2O

___ FeS + ___ HCl ___ H2S + ___ FeCl2

How many toy tractor trailers can you make from the following?

350 g of tires1125 g of truck frames87 g of seats15 g of steering wheels

What additional information would you need to answer this problem?

Reaction Stoichiometry

Composition stoichiometry – deals with the mass relationships of elements in compounds Ie. Mg(OH)2 – contains 1 Mg, 2 O, and 2 H

Reaction stoichiometry – involves the mass relationships between reactants and products in a chemical reaction Ie. 1C4H8 + 6O2 4CO2 + 4H2O

WE CAN ONLY COMPARE RELATIONSHIPS BETWEEN

REACTANTS AND PRODUCTS USING MOLES

Reaction-Stoichiometry Problems

Problem Type 1Given: Amt of Cmpd A in mol Unknown: Amt of Cmpd B in mol

mol A mol B

Problem Type 2Given: Amt of Cmpd A in molUnknown: Amt of Cmpd B in grams

mol A mol B grams of B

Problem Type 4Given: Mass of Cmpd A in gramsUnknown: Mass of Cmpd B in gramsGrams of A mol A mol

B grams B

Problem Type 3Given: Mass of Cmpd A in gramsUnknown: Amt of Cmpd B in mol

Grams of A mol A mol B

How should be solve these problems?

2Al2O3 4Al + 3O2

Given: mol Al Unknown: mol O2

2HgO 2Hg + O2

Given: g HgO Unknown: mol Hg

4NH3 + 6NO 5N2 + 6H2O

Given: mol NO Unknown g H2O

2Al + 3H2SO4 Al2(SO4)3 + 3H2

Given: g Al Unknown: g aluminum sulfate

Mole Ratio

Mole ratio – a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction

2Al2O3 4Al + 3O2

2 mol Al2O3 or 4 mol Al .

4 mol Al 2 mol Al2O3

2 mol Al2O3 or 3 mol O2 .

3 mol O2 2 mol Al2O3

4 mol Al or 3 mol O2

3 mol O2 4 mol Al

What mole ratios can we make? 2Al2O3 4Al + 3O2

2HgO 2Hg + O2

4NH3 + 6NO 5N2 + 6H2O

2Al + 3H2SO4 Al2(SO4)3 + 3H2

4NH3 + 6NO 5N2 + 6H2O

You have 0.345g ammonia.1. How many grams of nitrogen monoxide

do you need?2. How many cL of nitrogen gas are

produced?3. Water has a density of 1g/mL. How

many cm3 of water is produced?

4NH3 + 6NO 5N2 + 6H2O

You have 0.345g ammonia.

1. How many grams of nitrogen monoxide do you need?

2. How many cL of nitrogen gas are produced?

3. Water has a density of 1g/mL. How many cm3 of water is produced?