4.02 chemical reactionsfaculty.sdmiramar.edu/.../04_bondingreactions/402/402_chemrxn.pdf · 2...

January 10 1 Chemical Reactions

4.02 Chemical Reactions

Dr. Fred Omega Garces Chemistry 111 Miramar College

The Law of Conservation of Mass


Chemical Reactions; the heart of chemistry is the chemical reaction which is responsible for making new substances. If the reaction is new, then it is similar to inventing a new product.

Synthesis of: Nylon:

Aspirin: Salicylic acid + acetic anhydride g Aspirin (acetylsalicylic acid)

Glucose: CO2 + H2O + hν g C6H12O6

Making Substances

COHO

O CCH3

O

Acetylsalicyclic acid(Aspirin)

COHO

O H

+

OC

CH3

OC

H3C

O OC

CH3

OH

Air Bag: 2Na3N (s) + 3O(s) _ 3Na2O (s) + N2 (g)


The Law of Conservation of Mass Chemical reactions are based on the "Law of conservation of mass". Σ Atoms reacting = Σ Atoms produced Before reaction After reaction

i) 12 H2 + 6 N2 g 8 NH3 + 2N2 (excess)

i) 24 H’s + 12 N’s g 24 H’s + 12 N’s

ii) C3H8 + 5 O2 g 3 CO2 + 4H2O

+ +


Reaction Process

Note: 18 H and 6 N on each side of the chemical equation !! The net molecular equation is:

9 H2 (g) + 3 N2 (g) g 6 NH3 (g)

Symbol Meaning + and or plus a reacts to form or yields

(s) Solid

(l) liquid (g) gas

(aq) aqueous (water) solution Heat added

Catalyst (in this case, platinum)

Δ" → " "

Pt! → ! !

9 H2(g) + 6 N2 (g) g 6 NH3 (g) + 3 N 2 (g) (excess N2)

Atoms in reactant = Atoms in product

2 NH 3

2 NH 3

2 NH 3

H 2 H 2

N 2

N 2

H 2

H 2

H 2

H 2 H 2

H 2 H 2

N 2

N 2

N 2

N 2


Evidence of a Chemical Change Chemical change requires that reactant bonds are broken and product bonds form.

The chemical identity of the starting material is altered. This can be detected by making physical observations during the reaction.

Evidence: 1.  Gas formation: Combustion of ethanol.

2.  Precipitation or solid formation: BaCl2 and Potassium chromate.

3.  Temperature change: NaOH in water.

4.  Color change: Pigments or reactions.


Chemical Reactions

(g) (g) (g) (l) Δ

Reactants Products P4 (s) + 6 Cl2 (g) → 4 PCl3 (s)

1 molecule 6 molecules → 4 molecules 1.00 mole 6.00 moles → 4.00 moles


Generic Form

aA + bB → c C + dD Where A, B, C and D are specie (compounds) that are involve in the reaction. a, b, c and d are coefficient that tell how many of each species react. # of atoms (reacted) = # of atoms (produced)

C3H8 (g) + 5 O2 (g) g 3 CO2 (g) + 4 H2O (g)

Species: C3H8 (propane), O2 (oxygen), CO2 (carbon dioxide), H2O (water) Number of species: 1 (propane), 5 O2 (oxygen), 3 (carbon dioxide) and 4 (water)

+ +


Balancing Process

* Note: Once the formula for the substance is established, (i.e., the chemicals involved in the reaction are determined) the subscript can never be changed. Only the coefficient can be altered. MgO cannot be changed to MgO2 just to balance the equation. Furthermore, MgO2 is not chemically sound.

Consider the following reaction:

To balance this equation: Mg + O2 g MgO2 i) No!! (never since MgO2 is different from MgO) Mg + O2 g 2 MgO ii) Oxygen balanced, but Mg is not balanced

2 Mg + O2 g 2 MgO ii) Correct, all species are balanced

Mg + O2 g MgO magnesium Oxygen from air Product


Type of Reactions 1. Combination Reaction A + B g AB Example: i) __ SO3 + __ H2O g __ H2SO4 ii) __ P + __ S g __ P2S5 iii) __ N2 + __ H2 g __ NH3 2. Decomposition Reaction AB g A + B Example: i) __ H2CO3 g __ H2O + __ CO2 ii) __ KClO3 g __ KCl + __ O2 3. Single Displacement Reaction: A + BC g AC + B Example: i) __ Zn + __ Cu(NO3)2 g __ Zn(NO3)2 + __ Cu ii) __ Ca + __ H2O g __ Ca(OH)2 + __ H2

4a. Double Displacement Reaction: AB + CD g AD + CB Example: i) __ Ba(NO3)2 + __ H2S g __ BaS + __ HNO3 ii) __ MgCl2 + __ Na3PO4 g __ Mg3(PO4)2 + __ NaCl 4b. Acid Base (Double Displacement) Reaction: HA + MOH g H2O + MA Example: i) __ HNO3 + __ Ba(OH)2 g __ H2O + __ Ba(NO3)2 ii) __ HCl + __ NH4OH g __ H2O + __ NH4Cl 5. Combustion Reaction CxHy + O2 g CO2 + H2O Example: i) __ C4H10 + __ O2 g __ CO2 + __ H2O ii) __ C6H12O6 + __ O2 g __ CO2 + __ H2O


Balancing (Guidelines)

Summary : Balancing chemical reaction • Box the chemical and do not change the formula. • Assign coefficient of 1 to the most complicated molecule. • Balance elemental chemicals last. i.e., H2, N2, O2 • Use fraction coefficient to balance odd number of atoms in the equation. • Balance polyatomic cations / anions as a single unit if these ions occur in

reactant and product unchanged (i.e., PO43- and SO4

2- ) • Convert fraction to integer.

1 H2 + O2 H2O

2H 2O 2H 1O

Chemical identified oxygen is not balance

H2O2 ?

Cannot since identity will be change d

2 H2 + O2 2 H2O Change coefficient of product to two waters (H2O)

2H's, 2 O's 4H's, 2O's

Oxygen is balanced but hydrogen is not. Coefficient must be adjusted

3 2 H2 + O2 2 H2O Two placed in front of H2, to change H atom to four

4H's, 2 O's 4H's, 2O's

2 O's and 4 H's are on each side of the balanced equation

4 2 H2 + O2 2 H2O The equation is now balanced


Summary : Balancing chemical reaction

1• Box the chemicals so that you don’t change the formula.

2• Assign a coefficient of one to the most complicated molecular specie. Ex#1 - 5

3• Balance elemental chemicals last. i.e., H2 N2 O2 Ex#2 & 3

4• Use fractional coefficients to balance an odd number of atoms in the equation Ex#2 & 3

5• Convert the fraction to integer by multiplying through whole equation by the denominator of the fraction Ex#2 & 3

6• Balance polyatomic cation / anion as a single unit if these ions occurs in reactant and product unchanged (i.e., PO4

3- and SO4

2- ). Ex#4 & 5


Example: Balancing Reactions

#1 Sodium oxide and water forms sodium hydroxide #2 Ferric(III) Sulfide & molecular oxygen yields ferric(III) oxide & sulfur dioxide #3 C5H12 (g) + O2 (g) g H2O(g) + CO2 (g) #4 H2SO4 (aq) + Ca(OH)2 (aq) g H2O(l) + CaSO4 (s) #5 Ca3(PO4)2 (s) + H2SO4 (aq) g CaSO4 (s) + H3PO4 (aq)

Na2O + H2O g 2NaOH

Fe2S3 + 9/2 O2 g Fe2O3 + 3SO2 convert to integer by multiplying by 2

C7H14 (g) + 21/2 O2 (g) g 7H2O(g) + 7CO2 (g)



#1 Sodium oxide and water forms sodium hydroxide #2 Ferric(III) Sulfide & molecular oxygen yields ferric(III) oxide & sulfur dioxide

+ __H2O __NaOH __Na2O g

__Fe2S3 + __O2 __Fe2O3 + __SO2 g Fe2S3 + 9/2 O2 g Fe2O3 + 3SO2

1 + 1 g 2

1 + 9/2 g 1 + 3

Sum Coef. a) 3 b) 4 c) 5 d) 6

Sum Coef. a) 10 b) 14 c) 19 d) None



#3 C5H12 (g) + O2 (g) g H2O(g) + CO2 (g) #4 H2SO4 (aq) + Ca(OH)2 (aq) g H2O(l) + CaSO4 (s)

__C5H12 (g) + __O2 (g) __H2O(g) __CO2 (g) g

__H2SO4 (aq) + __Ca(OH)2 (aq) __H2O(l) + __CaSO4 (s) g

Sum Coef. a) 13 b) 20 c) 18 d) None

1 + 8 g 6 + 5

Sum Coef. a) 4 b) 5 c) 10 d) None 1 + 1 g 2 + 1



#1 Sodium oxide and water forms sodium hydroxide #2 Ferric(III) Sulfide & molecular oxygen yields ferric(III) oxide & sulfur dioxide #3 C7H14 (g) + O2 (g) g H2O(g) + CO2 (g) #4 H2SO4 (aq) + Ca(OH)2 (aq) g H2O(l) + CaSO4 (s) #5 Ca3(PO4)2 (s) + H2SO4 (aq) g CaSO4 (s) + H3PO4 (aq)

Na2O + H2O g 2NaOH

Fe2S3 + 9/2 O2 g Fe2O3 + 3SO2 convert to integer by multiplying by 2

C7H14 (g) + 21/2 O2 (g) g 7H2O(g) + 7CO2 (g)


Type of Reactions (1): Combination

1. Combination Reaction -A Reaction in which two substances chemically combine to form a third. A + B g AB Example: i) __ SO3 (g) + __ H2O (l) g __ H2SO4 (aq)

ii) __ P4 (s) + __ S8 (s) g __ P2S5 (s)

iii) __ Al(s) + __ Br2 (l) g __ Al2Br6 (s)

1:1:1

16:5:8

2:3:1


Type of Reactions (2): Decomposition

2. Decomposition Reaction -A Reaction in which a single compound breaks up into two or more other substances. AB g A + B Example: i) __ H2CO3 (aq) g __ H2O(l) + __ CO2 (g)

ii) __ KClO3 (s) g __ KCl(s) + __ O2 (g)

iii) __ HgO(s) g __ Hg (l) + __ O2 (g)

1:1:1

2:2:3

2:2:1


Type of Reactions (3): Single displacement

C. Single Displacement Reaction -A Reaction in which one element reacts by replacing another element in a compound. A + BC g AC + B Example: i) __ Zn (s) + __ Cu(NO3)2 (aq) g __ Zn(NO3)2 (aq) + __ Cu (s)

ii) __ Ca (s) + __ H2O (l) g __ Ca(OH)2 (aq) + __ H2 (aq)

iii) __ Cu(s) + __ AgNO3 (aq) g __ Cu(NO3)2 (aq) + __ Ag(s)

1:1:1:1

1:2:1:1


Type of Reactions (4a) Double Displacement (Chp8) 4a. Double Displacement Reaction: - A Reaction in which two

compounds exchange partners to form two new compounds. AB + CD g AD + CB Example: i) __ Ba(NO3)2 (aq) + __ H2S (aq) g __ BaS(s) + __ HNO3 (aq)

ii) __ MgCl2 (aq) + __ Na3PO4 (aq) g __ Mg3(PO4)2 (s) + __ NaCl (aq)

iii) __ Ba(NO3)2 (aq)+ __ K2CrO4 (aq) g __ BaCrO4 (s) + __ KNO3 (aq)

1:1:1:2

3:2:1:6


Type of Reactions (4) Driving Force for Reactivity

Factors Towards Reactivity 1. Gas formation (Low molar mass covalent molecule) __ZnS(s) + __ HCl (aq) g __ZnCl2 (aq) + __H2S (g) __HNO3(aq) + __NaCN(aq) g __ NaNO3 (aq) + __HCN (g)

2. Weak Electrolyte or water formation (Neutralization) __HI(aq) + __Al(OH)3 (s) g __H2O (l) + __AlI3 (aq) __LiOH(aq) + __HNO3 (aq) g __LiNO3(aq) + __H2O (l)

3. Precipitation formation (Solubility Table)

__Pb(NO3)2 (aq) + __NaCl(aq) g __ NaNO3 (aq) + __PbCl2(s) __MnS(s) + __ H2SO4 (aq) g ????


Type of Reactions (4b): Neutralization, a type of double displacement

4b. Acid-Base (Neutralization Reaction): -A Reaction that occurs between an acid and a base with the formation of an ionic compound and water.

HA + MOH g H2O + MA Example: i) __ HNO3 (aq) + __ NaOH (aq) g __ H2O (l) + __ NaNO3 (aq)

ii) __ H3PO4 (aq) + __ NH3 (aq) g __ H2O(l) + __ (NH4)3PO4 (aq)

1:1:1:1

1:3:1:1


Type of Reactions (5) Combustion

5. Combustion Reaction -A Reaction of a substance with either pure oxygen or oxygen in the air with the rapid release of heat and the appearance of a flame.

CxHy + O2 g CO2 + H2O Example:

i) __ C6H12O6 (l) + __ O2 (g) g __ CO2 (g) + __ H2O(l) ii) __ C4H10 (l) + __ O2 (g) g __ CO2 (g) + __ H2O (l)

2:13:8:10 2:13:8:10

1:6:6:6


Summary Understand the Basic idea of a Chemical Reaction

Write and Balance a Chemical Reaction

Recognize the different chemical reactions

1. Combination

2. Decomposition

3. Single Displacement

4. Double Displacement

5. Combustion

4.02 chemical reactionsfaculty.sdmiramar.edu/.../04_bondingreactions/402/402_chemrxn.pdf · 2...

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