We can’t measure moles!!• What can we do?

• We can convert grams to moles.

• Periodic Table

• Then use moles to change chemicals

• Balanced equation

• Then turn the moles back to grams.

• Periodic table

Periodic Table

MolesA

MolesB

Massg B

Periodic Table

Balanced Equation

Massg A

•Decide where to start based on the units you are given

•and stop based on what unit you are asked for

Reaction StoichiometryStoichiometry: quantitative relationship among reactants and products in a balanced reaction equation. Quantities may be in mole, mass, weight, or volume.

How much KCl and O2 are produced by decomposing 123.0 g of KClO3?

2 KClO3(s) 2 KCl (s) + 3 O2 (g)

245.2 g 149.2 g 96 g123.0 x y

use proportionality to get x = 74.8 g KCl; y = 48.2 g O2

Stoichiometry Calculations

123.0 g KClO3

How much KCl and O2 are produced by decomposing 123.0 g of KClO3?

2 KClO3(s) 2 KCl (s) + 3 O2 (g)

245.2 g 149.2 g 96 g123.0 x y

use proportionality to get x = 74.8 g KCl; y = 48.2 g O2

96.0 g O2

245.2 g KClO3

1 mol O2

32.0 g O2

22.4 L O2

1 mol O2

Versatile , getting the amount in various units.

Find amount of KCl in g, mol, and volume (specific gravity = 1.984)

123.0 g KClO3

The Steps in a Stoichiometric Calculation

Mass of substance A

Moles of substance A

Moles of substance B

Mass of substance B

Use molar mass of AUse molar mass of A

Use molar mass of BUse molar mass of B

Use coefficients of A & B in Use coefficients of A & B in balanced eqnbalanced eqn

Conversions

• 2C2H2 + 5 O2 4CO2 + 2 H2O

• How many moles of C2H2 are needed to

produce 8.95 g of H2O?

• If 2.47 moles of C2H2 are burned, how

many g of CO2 are formed?

For example...• If 10.1 g of Fe are added to a solution of

Copper (II) Sulfate, how much solid copper would form?

• Fe + CuSO4 Fe2(SO4)3 + Cu

• 2Fe + 3CuSO4 Fe2(SO4)3 + 3Cu 10.1 g Fe

55.85 g Fe1 mol Fe

2 mol Fe3 mol Cu

1 mol Cu63.55 g Cu

= 17.3 g Cu

2Fe + 3CuSO4 Fe2(SO4)3 + 3Cu

0.181 mol Fe2 mol Fe

3 mol Cu= 0.272 mol Cu

0.272 mol Cu1 mol Cu63.55 g Cu

= 17.3 g Cu

Could have done it

10.1 g Fe55.85 g Fe1 mol Fe

2 mol Fe3 mol Cu

1 mol Cu63.55 g Cu

= 17.3 g Cu

More Examples• To make silicon for computer chips they use

this reaction

• SiCl4 + 2Mg 2MgCl2 + Si

• How many moles of Mg are needed to make 9.3 g of Si?

• 3.74 mol of Mg would make how many moles of Si?

• How many grams of MgCl2 are produced along

with 9.3 g of silicon?

For Example• The U. S. Space Shuttle boosters use this

reaction

• 3 Al(s) + 3 NH4ClO4

Al2O3 + AlCl3 + 3 NO + 6H2O

• How much Al must be used to react with 652 g of NH4ClO4 ?

• How much water is produced?

• How much AlCl3?

Example

Calculate the mass of sulfur dioxide (SO2) produced when 3.84 mol O2 is reacted with FeS2 according to the equation:

4FeS2 + 11O2 2Fe2O3 + 8SO2

3.84 mol m = ?m = ?2.79 mol

Another Example

One of the most spectacular reactions of aluminium, the thermite reaction, is with iron oxide, Fe2O3, by which metallic iron is made.

The equation is :

2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l)

A certain welding operation, requires that at least 86.0 g of Fe be produced. What is the minimum mass in grams of Fe2O3 that must be used for the operation?

Calculate also how many grams of aluminium are needed.

Strategy:

2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l)

mass of Fe mol of Fe

mol of Fe mol of Fe2O3

mol of Fe2O3 mass of Fe2O3

Examples

• One way of producing O2(g) involves the

decomposition of potassium chlorate into potassium chloride and oxygen gas. A 25.5 g sample of Potassium chlorate is decomposed. How many moles of O2(g)

are produced? • How many grams of potassium chloride?• How many grams of oxygen?

Examples

• A piece of aluminum foil 5.11 in x 3.23 in x 0.0381 in is dissolved in excess HCl(aq). How many grams of H2(g) are produced?

• How many grams of each reactant are needed to produce 15 grams of iron form the following reaction? Fe2O3(s) + Al(s) Fe(s) + Al2O3(s)

Examples

• K2PtCl4(aq) + NH3(aq)

Pt(NH3)2Cl2 (s)+ KCl(aq)

• what mass of Pt(NH3)2Cl2 can be

produced from 65 g of K2PtCl4 ?

• How much KCl will be produced?

• How much from 65 grams of NH3?

How do you get good at this?

Gases and Reactions

We can also change• Liters of a gas to moles

• At STP

• 0ºC and 1 atmosphere pressure

• At STP 22.4 L of a gas = 1 mole

• If 6.45 moles of water are decomposed, how many liters of oxygen will be produced at STP?

For Example• If 6.45 grams of water are decomposed,

how many liters of oxygen will be produced at STP?

• H2O H2 + O2

• 2H2O 2H2 + O2

6.45 g H2O 18.02 g H2O1 mol H2O

2 mol H2O1 mol O2

1 mol O2

22.4 L O2

Your Turn

• How many liters of CO2 at STP will be

produced from the complete combustion of 23.2 g C4H10 ?

• What volume of oxygen will be required?

Example• How many liters of CH4 at STP are required to

completely react with 17.5 L of O2 ?

• CH4 + 2O2 CO2 + 2H2O

17.5 L O2 22.4 L O2 1 mol O2

2 mol O2 1 mol CH4

1 mol CH4 22.4 L CH4

= 8.75 L CH4

22.4 L O2 1 mol O2

1 mol CH4 22.4 L CH4

Avagadro told us• Equal volumes of gas, at the same

temperature and pressure contain the same number of particles.

• Moles are numbers of particles

• You can treat reactions as if they happen liters at a time, as long as you keep the temperature and pressure the same.

Example

• How many liters of CO2 at STP are

produced by completely burning 17.5 L of CH4 ?

• CH4 + 2O2 CO2 + 2H2O

17.5 L CH4 1 L CH4 1 L CO2

= 17.5 L CO2

Avogadro’s Principle of Gas Volumes: 9.2 #4

For balanced chemical eqns:

1 (mol) H + 1 (mol) Cl => 1 (mol) HCl (or volume) + (or volume) => 1 (or volume) HCl

2 (mol) H + 1 (mol) O => 1 (mol) H2O

What if: 1 “volume” contained 1 mol of H? How many “volumes” of O needed for balanced rxn?

How many volumes of H2O produced?

Significance of this Relationship 9.2 #5

2 H(g) + 1 O(g) => 1 H2O(g)

2 atoms 1 atom 1 molecule

2 moles 1 moles 1 mole

** 2 “volumes” 1 volume 1 volume

**A “volume” stoichiometry! This kind of stoichiometry holds just like mole stoichiometry, IFF all gaseous reactants and products are at the same T and P.

The Ideal Gas Law 9.3 #1

P V = n R T

•Use to describe some aspect of a gas under any single set of conditions

•Calculate moles, density or MW w this formula which is not limited to std state conditions

•Restrictions: applies to “Ideal Gas” and must use: P in atm V in L T in K (R=0.0821 L-atm/mol K)

Ideal Gases 9.3 #2

• Gases where each molecule in the gas sample is completely independent of one other:– molecules occupy no space (point masses)– No intermolecular interactions– Collisions completely elastic (no E lost)

• Ideal gases obey PV = nRT• No real gas is truly ideal; but, most gases obey IGL• Expect sig. dev. w conditions that allow high

intermolecular interactions (highly conc., low T, polar molecules).

Examples 9-9.4 #1

What P is exerted by 1.8 mol N2 in a 5.2 L vessel at 65 ˚C?

5.12 g of H2(g) exerts 4.1 atm P in a 2.0 L vessel. Find T.

What is the density of H2(g) if a 0.500 L sample exerts 3.5 atm of P at 200 K? Answers: 9.6 atm ; 38 K ; 0.107 mol H2 (0.213 g; 0.43 g/L)

Example- Try at home 9-9.4 #2

Gas A (1 L) is mixed with gas B (2 L) both at the same T. A and B react quantitatively to produce 1 L of product at T. The 1 L product occupies 5.7 L at STP.

a. What is the product of the reaction? (100% yield)

b. How many moles of product are produced?c. How many moles of B were reacted?d. What would the P of the product be in a 10 L

vessel at 250 K?

Answers: a) AB2 b) 0.23 mol c) 0.46 mol d) 0.47 atm

Example Stoich. Relationships 9.4 #3

Assume constant T and P. How many L of O2(g) are

needed to completely react with 14.0 L of C4H10?

2 C4H10(g) + 13 O2(g) => 8 CO2(g) + 10 H2O(l)

The label on a gas cylinder is obscured. It could be Ne or N2. The gas (2.50 g) occupies 2.00 L at 1.00

atm and 273 K. What is the gas?

Solutions

PV=nRT n = (PV)/(RT) n = 0.0892 mol gasProblem states gas sample is 2.50 g.

MW = g / mol = 2.50 g/ 0.0892 mol = 28.2 g/mol = N2(g)

Constant T and P, so ‘equal volumes’ contain ‘equal moles’.

2 C4H10(g) + 13 O2(g) => 8 CO2(g) + 10 H2O(l)

14.0 L of C4H10 x (13L O2/2 L C4H10) = 91 L O2(g)

Example Stoich. Relationships 9.4 #4

a. A sample of H2(g) occupies 5.00 L at STP.

How many grams of H2(g) are present?

b. A sample of Cl2(g) occupies 10.0 L at 4 atm at 273 K. How many L of Cl2(g) are needed for a reaction with H2(g) using: H2(g) + Cl2(g) => 2 HCl(g)

Answer: a) 0.22 mol=0.44g ; b) 10 L at 4 atm, 273 K

Real Gases and Ideal Gas Law 9.8

• Real gases not ideal but deviations usually small. • Van der Waals equation adjusts for ‘sticky force’

interactions and volume occupied by the gas.-if molecules attracted to each other they don’t exert as much pressure on container, and if the T is low or conc. high occupied volume significant and interactions incr.

(P + n2a/V2) (V-nb) = nRT

a & b terms specific to each gas (can look up in tables)Corrected P Corrected V

Solution Stoichiometry

Solutions and Concentrations

Concentrations are expressed in many ways, g / 100 mL, g / L, mol / L (= M), mole fraction, weight fraction, percentage etc.

Molarity is the expression of concentration in mole per liter.

Explain solvent, solute, solution, and mixture

For quantities in reactions:

Amount = concentration * volume

C1 V1 = C2 V2