Chapter Five Chemical Quantities and Reactions

The Mole Molar Mass Chemical Changes Chemical Equations Types of Reactions Mole Relationships in Chemical Equations Mass Calculations Energy in Chemical Reactions

The Mole Many things

have names for a quantity or group.

In chemistry, a quantity of atoms, molecules, etc. is called a mole.

The Mole

Why a “mole”?

The Mole A mole of anything is 6.02 E+23 particles. This is sometimes referred to as

Avogadro’s Number. Written as a number:

602,000,000,000,000,000,000,000 A mole of marbles would easily fill the

entire Grand Canyon with much to spare.

The Mole One mole of:

Carbon = 6.02 E+23 carbon atoms CO2 =6.02 E+23 CO2 molecules NaCl = 6.02 E+23 NaCl formula units 1 mole of anything = 6.02 E+23

particles

anything of mole 1

particles 10 6.02or

particles 10 02.6

anything of mole 1 23

23

Learning Check

Ex) Convert 0.0242 moles of CH4 to molecules.

Learning Check Ex) Convert 4.45 E+21 atoms of Zn

to moles.

Subscripts and Moles The subscripts in a formula can be

interpreted on either an atom or mole level.

Ex) C6H12O6

Learning Check Ex) How many moles of H atoms are

present in 0.0150 moles of NH3? How many H atoms?

Molar Mass A molar mass of

an element is the atomic mass expressed in grams.

The molar mass of carbon is 12.01g

Molar Mass The molar mass of any compound is

equal to the sum of all the atomic weights for each element in the formula.

Ex) The molar mass of CO2 is:1C + 2O = 1(12.0g) + 2(16.0g) = 44.0gThus, 1 mole of CO2 = 44.0g

Learning Check

What is the molar mass of MgCl2?a) 94.0gb) 59.8gc) 95.3gd) 119.6g

Learning Check

What is the molar mass of Al(OH)3?a) 78.0gb) 46.0gc) 132.0gd) 44.0g

Molar Mass Any molar mass can written as a

conversion factor. From earlier:

1 mole of CO2 = 44.0g

2

2

CO mole 1

g 44.0or

g 0.44

CO mole 1

Molar Mass This allows for the conversion

between grams and moles. Ex) 45.0g of BaCl2 = ? moles

Molar Mass Ex) 1.52 x 10-3 moles of phosphorous

tribromide = ? grams

Moles Combining both molar mass and

Avogadro’s number concepts.

Learning Check

An 8.15 E+21 molecules of C2H6

would have a mass of:

Learning Check A 45.3g sample of lead(II) chloride

would contain how many formula units?

Learning Check

A 6.50 x 10-5 g sample of C5H10O5 will contain how many Hydrogen atoms?

Physical Changes A physical change is one in which

the state, shape, or size of the substance is altered but not its identity. Ex) Ice melting Ex) Ripping a piece of paper Ex) Boiling ethanol Ex) Pulverizing a rock

Chemical Changes A chemical change is one in which

matter is transformed into new kinds of matter by the rearrangement of atoms. Ex) Iron rusting Ex) Burning a log Ex) Fermenting grapes Ex) Antacid neutralizing stomach acid

Learning Check Decide whether each is Physical or

Chemical change. a) Making Kool-aid b) Baking cookies c) Cutting an aspirin in half d) Bleaching a stained shirt

Chemical Equations Shows the before and after for a

chemical reaction using chemical formulas.

Chemical Equations Symbols added

having various meanings.

Chemical Equations A Chemical Equation is always

written so that the total numbers of atoms on each side of the equation are equal.

To do this, coefficients are added in front of each substance.

Must use lowest whole number coefficients!

Chemical Equations

__Al + __Cl2 __AlCl3

Reaction is NOT balanced! Note: can NOT alter any subscripts! Make a tally sheet.

Learning Check Balance the following:

__FeCl2 + __Al __AlCl3 + __Fe

__Al2(SO4)3 + KOH Al(OH)3 + K2SO4

Learning Check Balance the following:

__H3PO3 __H3PO4 + __PH3

__C3H8 + __O2 __CO2 + __H2O

Learning Check Balance the following:

__C4H8O + __O2 __CO2 + __H2O

Types of Reactions Combination Reaction

2Al(s) + 3Br2(l) 2AlBr3(s) CaO(s) + CO2(g) CaCO3(s)

Types of Reactions Decomposition Reaction

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

Types of Reactions

Single Replacement Reactions

Mg(s) + CuCl2(s) MgCl2(s) + Cu(s)

Types of Reactions

Double Replacement Reactions

Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)

Combustion

A rapid reaction with oxygen from the air. CH4(g) + 2O2(g) CO2(g) + 2H2O(l)

Also occurs in the cells of animals when glucose, C6H12O6, is converted to energy.

Chemical Reactions A reaction can be interpreted in

many ways. Atoms and molecules Moles Masses

Chemical Reactions

N2 + 3 H2 2 NH3

Molecular interpretation

Mole interpretation

Mass interpretation

Law of Conservation of Mass

In any chemical reaction, matter cannot be created nor destroyed.

Masses of reactants = Masses of products.

N2 H2 NH3

15 molecules

2.4 moles

0.014 moles

Stoichiometry The calculation of chemical

quantities in a reaction. Relates a mass of a reactant or

product to any other reactant or product.

Stoichiometry

Mass of A

Moles of A Moles of B

Mass of B

Stoichiometry

If 45.1g of N2 are used, then what mass of H2 is required?

N g 1.45 2

Stoichiometry

If 7.25g of H2 completely reacts, what mass of NH3 is produced?

H g 25.7 2

Stoichiometry For the reaction:

2C2H2 + 5O2 4CO2 + 2H2O

If 6.85g of C2H2 is completely combusted, then what mass of CO2 is produced? a. 13.7g b. 11.6g c. 23.2g d. 5.80g

Stoichiometry For the reaction:

4Al + 3O2 2Al2O3

When 0.452g of Al completely reacts, what mass of Al2O3 is produced? a. 3.42g b. 0.853g c. 0.226g d. 23.1g

Energy in Reactions

Collision Theory In the game of pool (billiards), in order

to sink a ball in the pocket what is needed?

In reactions, what is needed?

Activation Energy The activation

energy is the minimum amount of energy required to produce a reaction.

Exo- and Endothermic Reactions

Reactions that release heat energy are said to be ________________.

Reactions that absorb heat energy are said to be ________________.

Exo- and Endothermic Reactions

Exothermic Reactions

Energy level of the products is lower than that of the reactants.

Heat is a product and can be included in the balanced reaction.

Ex) C(s) + 2H2(g) CH4(g) + 18 kcal

Endothermic Reactions

Energy level of the products is higher than that of the reactants.

Heat is a reactant.

Ex) N2(g) + O2 (g) + 43.3 kcal 2NO(g)

Rate of a Reaction

Reactions can range from instantaneous (very fast) to very slow.

We can affect the rate of reaction by: Increasing the concentration of the

reactants.

Rate of a Reaction Increasing the

temperature of the reactants. This increases the fraction of molecules that have enough energy to react.

Adding a catalyst. A catalyst lowers the activation energy.

2H2O2(aq) 2H2O(l) + O2(g)