Chapter 3 Chemical Reactions. Chemical Change Evidence Chapter 6

Chapter 3Chemical Reactions

Chemical Change Evidence

Chapter 6


Chapter 6

What is a clue that a chemical reaction has occurred?

a) The color changes.

b) A solid forms.

c) Bubbles are present.

d) A flame is produced.


Chapter 6


“Colorless hydrochloric acid is added to a red solution of cobalt(II) nitrate, turning the solution blue.”

a) The color changes.

b) A solid forms.




Chapter 6


“A solid forms when a solution of sodium dichromate is added to a solution of lead nitrate.”

a) A gas forms.

b) A solid forms.



Chapter 6

Chemical Reactions• A chemical equation is an abbreviated way to

show a chemical or physical change• A chemical change alters the physical and

chemical properties of a substance• Factors that indicate a chemical change

Change in color Temperature change Change in odor Change in taste (we do not taste chemicals)

• Reactions always contain an arrow that separates the reactants from the products

Reactants Products

Types of Chemical Reactions• Combination reaction (synthesis)

Elements for reactants Examples:

H2 + O2 H2O

N2 + H2 NH3

Al + O2 Al2O3

The Law of Conservation of matter, states matter cannot be created nor destroyed, the means equations must be balanced.

Types of Chemical ReactionsBalance the first equation

H2 + O2 H2O

Note two oxygen atoms on the reactant side and only one on the product side, therefore place a two in front of water


H2 + O2 2H2O


The two now doubles everything in water, thus 4 hydrogen and 2 oxygen. Now place a 2 in front of hydrogen.


2H2 + O2 2H2O


The two now doubles everything in water, thus 4 hydrogen and 2 oxygen. Now place a 2 in front of hydrogen.

Types of Chemical ReactionsNow balance the second equation

N2 + H2 NH3

Note two nitrogen atoms on the reactant side and only one on the product side.

Place a 2 in front of ammonia


N2 + H2 2NH3


Place a 2 in front of ammonia. This makes 2 nitrogen atoms and 6 hydrogen atoms. Now place a 3 in front of hydrogen to balance hydrogen atoms.


N2 + 3 H2 2NH3


Place a 2 in front of ammonia. This makes 2 nitrogen atoms and 6 hydrogen atoms. Now place a 3 in front of hydrogen to balance hydrogen atoms.

Types of Chemical Reactions• Decomposition Reaction

Compounds form simpler compounds or elements.

Examples

H2O H2 + O2



Examples

2H2O H2 + O2



Examples

2H2O 2H2 + O2

• Notice decomposition reactions are the opposite of combination reactions

Types of Chemical ReactionsSingle Replacement reactions have an element and a

compound for reactants.

Example:

Zn + HClHow do we predict the products? Trade places

with the metal or nonmetal with the metal or nonmetal in the compound

Types of Chemical ReactionsSingle Replacement reactions have an element

and a compound for reactants.

Example:

Zn + HCl

How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound

Types of Chemical ReactionsSingle Replacement reactions have an element and a compound for reactants.

Example:

Zn + HCl ZnCl + HNow make the products stable. Slide with Clyde

Types of Chemical ReactionsSingle Replacement reactions have an element and a compound for reactants.

Example:

Zn + HCl ZnCl2 + H2

Now make the products stable. Slide with Clyde

Types of Chemical ReactionsSingle Replacement reactions have an element and

a compound for reactants.

Example:

Zn + HCl ZnCl2 + H2


Now Balance

Types of Chemical ReactionsSingle Replacement reactions have an

element and a compound for reactants.

Example:

Zn + 2HCl ZnCl2 + H2


Now Balance

Types of Chemical Reactions

Single Replacement reactions have an element and a compound for reactants.

Another Example:

Cl2 + MgBr2

How do we predict the products? Trade places with the metal or nonmetal with the metal or nonmetal in the compound. In this case we are trading nonmetals


Single Replacement reactions have an element and a compound for reactants.

Another Example:

Cl2 + MgBr2 Br + MgCl


Types of Chemical ReactionsSingle Replacement reactions have an element

and a compound for reactants.

Another Example:

Cl2 + MgBr2 Br2 + MgCl2


Types of Chemical ReactionsDouble Replacement reactions contain compounds as

reactants.

HCl + Ca(OH)2 CaCl + HOH

Check formulas, and slide with Clyde when necessary

Types of Chemical ReactionsDouble Replacement reactions contain compounds

as reactants.

HCl + Ca(OH)2 CaCl2 + HOH


Types of Chemical ReactionsDouble Replacement reactions contain compounds

as reactants.

2HCl + Ca(OH)2 CaCl2 + 2HOH


Now Balance!


Combustion Reactions occur when an element or compound combine with oxygen to produce oxides of each element.

H2 + O2 CH4 + O2

What is the oxide of hydrogen?

Types of Chemical ReactionsCombustion Reactions occur when an element or

compound combine with oxygen to produce oxides of each element.

H2 + O2

CH4 +O2

What is the oxide of hydrogen? Water



H2 + O2 H2O

CH4 + O2


And the oxide of carbon?



H2 + O2 H2O

CH4 + O2 CO2 + H2O


And the oxide of carbon? Carbon dioxide



2H2 + O2 2H2O

CH4 + O2 CO2 + H2O

Now balance



2H2 + O2 2H2O

CH4 + O2 CO2 + 2H2O

Now balance



2H2 + O2 2H2O

CH4 + 2O2 CO2 + 2H2O

Now balance

The Chemical Package

• The baker uses a package called the dozen. All dozen packages contain 12 objects.

• The stationary store uses a package called a ream, which contains 500 sheets of paper.

• So what is the chemistry package?

About Packages

The Chemical Package

• The baker uses a package called the dozen. All dozen packages contain 12 objects.

• The stationary store uses a package called a ream, which contains 500 sheets of paper.

• So what is the chemistry package? Well, it is called the mole (Latin for heap).

About Packages

Each of the above packages contain a number of objects that are convenient to work with, for that particular discipline.

The atomic weights listed on the periodic chart are the weights of a mole of atoms. For example a mole of hydrogen atoms weighs 1.00797 g and a mole of carbon atoms weighs 12.01 g.

The MoleA mole contains 6.022X1023 particles, which is the number of carbon-12 atoms that will give a mass of 12.00 grams, which is a convenient number of atoms to work with in the chemistry laboratory.

Moles of ObjectsSuppose we order a mole of marshmallows for a chemistry party. How much space here at Central would be required to store the marshmallows?

Moles of Objects

Suppose we order a mole of marshmallows for a chemistry party. How much space here at Central would be required to store the marshmallows?Would cover the entire 50 states 60 miles deep

Moles of Objects


How about a mole of computer paper instead of a ream of computer paper, how far would that stretch?

Moles of Objects


How about a mole of computer paper instead of a ream of computer paper, how far would that stretch? Way past the planet Pluto!

To calculate the molar mass of a compound we sum together the atomic weights of the atoms that make up the formula of the compound. This is called the formula weight (MW, M).

Formula weights are the sum of atomic weights of atoms making up the formula.

The following outlines how to find the formula weight of water

symbol weight numberHO

1.0116.0

21X

X== 2.02

16.018.0 g/mole

Formula Weight Calculation

Percent Composition

Find the formula weight and the percent composition of

glucose (C6H12O6)

symbol weight number

HO

C

16.01.01

12.0

6

12

6

x

x

x

=

=

=

72.0

12.1296.0

180.1 g/mole

%C =

%H =

%O =

72.0

12.12

96.0

180.1

180.1

180.1

X =

X =

X =

40.0 %C

6.73 %H

53.3 %O

Law of Conservation of Mass• The law of

conservation of mass states that the sum of the masses of the reactants of a chemical equation is equal to the sum of the masses of the products.

Mole Calculations1. How many moles of Ca atoms are present in

20.0 g of calcium?

2. How many Cu atoms are present in 15.0 g of copper?

20.0 g Ca


20.0 g of calcium?


20.0 g Ca


20.0 g of calcium?


20.0 g Ca40.078 g Ca

Mole Ca


20.0 g of calcium?


20.0 g Ca40.078 g Ca

Mole Ca= 0.490 mole Ca


20.0 g of calcium?


20.0 g Ca40.078 g Ca


15.0 g Cu


20.0 g of calcium?


20.0 g Ca40.078 g Ca


15.0 g Cu

63.546 g Cu

Mole Cu


20.0 g of calcium?


20.0 g Ca40.078 g Ca


15.0 g Cu

63.546 g Cu

Mole Cu

Mole Cu

6.022X1023 atoms Cu


20.0 g of calcium?


20.0 g Ca40.078 g Ca


15.0 g Cu

63.546 g Cu

Mole Cu

Mole Cu

6.022X1023 atoms Cu

= 1.42X1023 atoms Cu

Empirical Formulas1. Assume there is 100 g of the sample, so the percent

composition will equal the number of grams of each element.

2. Convert the grams of each element into the moles of each element with their molar mass.

3. Divide the smallest number of moles of an element into the moles of each element present.

4. Convert the fractional ratios for each element into whole numbers by multiplying all the ratios by the same number.

5. The resulting numbers are the subscripts for the each element in the empirical formula.

Example Asbestos was used for years as an insulating

material in buildings until prolonged exposure to asbestos was demonstrated to cause lung cancer. Asbestos is a mineral containing magnesium, silicon, oxygen, and hydrogen. One form of asbestos, chrysotile (520.27 g/mol), has the composition 28.03% magnesium, 21.60% silicon, 1.16% hydrogen. Determine the empirical formula of chrysotile.

Molecular Formula

• The molecular formula can be determined from the percent composition and mass spectral data.

Example A combustion analysis of an unknown compound

indicated that it is 92. 23% C and 7.82% H. The mass spectrum indicated the molar mass is 78 g/mol. What is the molecular formula of this unknown compound?

Combustion Analysis

CaHb + excess O2 ---> a CO2(g) + b/2 H2O

The percent of carbon and hydrogen in CaHb can be determined from the mass of H2O and CO2 produced.

Combustion Analysis

Vitamin C is essential for the prevention of scurvy. Combustion of a 0.2000 g sample of this carbon, hyddrogen, oxygen compound yields 0.2998 g CO2 and 0.0819 g H2O. What is the empirical formula of vitamin C?

Mass Spectrometry• All Mass spectrometers separate atoms and

molecules by first converting them into ions and then separating those ions based on the ratio of their masses to their electric charges.

• Mass spectrometers are instruments used to determine the mass of substances.

Mass Spectrometer

Mass Spectra

Limiting Reactants

During photosynthesis a reaction mixture of carbon dioxide and water is converted to a molecule of glucose.

Limiting Reagents

• The limiting reactant is completely consumed in the chemical reaction. The amount of product formed depends on

the amount of limiting reagent available.

Example 10.0 g of methane (CH10.0 g of methane (CH44) is burned in 20.0 g of oxygen ) is burned in 20.0 g of oxygen

(O(O22) to produce carbon dioxide (CO) to produce carbon dioxide (CO22) and water ) and water (H(H22O). O).

a.a. What is the limiting reactant?What is the limiting reactant?

b.b. How many grams of water will be produced?How many grams of water will be produced?

Percent Yield

• Theoretical Yield:Theoretical Yield: the calculated the calculated amount of product formedamount of product formed

• Actual Yield:Actual Yield: the measured amount of the measured amount of product formedproduct formed

• Percent YieldPercent Yield = Actual Yield x = Actual Yield x 100%100% Theoretical Yield Theoretical Yield

Percent Yield ExampleAluminum burns in bromine liquid producing aluminum bromide. In a certain experiment, 6.0 g of aluminum was reacted with an excess of bromine to yield 50.3 g aluminum bromide. Calculate the theoretical and percent yields for this experiment.

The End

Documents

Chapter 3 Chemical Reactions. Chemical Change Evidence Chapter 6