CHEMICAL REACTION - WordPress.com · 09/08/2013 · Chemical Equation •A chemical ... Products...

CHEMICAL REACTION

Engr. Yvonne Ligaya F. Musico 1

Chemical Reaction


Introduction

– Chemical reactions occur when bonds between the

outermost parts of atoms are formed or broken

– Chemical reactions involve changes in matter, the

making of new materials with new properties, and

energy changes.

– Symbols represent elements, formulas describe

compounds, chemical equations describe a

chemical reaction


Chemical Equation

• A chemical equation illustrates the formulas

and quantities of reactants and products in a

chemical reaction.

• It is an expression that uses symbols to

describe a chemical change.


Components of Chemical Equation

COMPONENTS DEFINITION

Reactants Substances present at the beginning of the reaction

Products The substances formed in a chemical reaction

+ If in reactant, read as “reacts with”, “combines with” If in product, read as “and”

→ produces, yields, forms and shows the direction of the chemical reaction

State of substances: (s) (l) (g) (aq)

Solid Liquid Gas Aqueous


Components of Chemical Equation

COMPONENTS DEFINITION

↑ The product is gaseous and escapes

↓ Precipitate is formed

→ ←

Reversible reaction

The reaction involves “heating”

Catalyst is used to undergo chemical reaction

∆H Amount of energy involved in chemical reaction


catalyst

Things to Remember About Writing

Chemical Equation

– Don’t forget about the diatomic elements!

(BrINClHOF) For example, Oxygen is O2 as an

element. In a compound, it can’t be a diatomic

element because it’s not an element anymore, it’s a

compound!

– The Law of Conservation of Mass holds for every

chemical equation.


Steps to Writing Reactions

Some steps for doing reactions

1. Identify the type of reaction

2. Predict the product(s) using the type of reaction

as a model

3. Balance it


Types of Reactions

There are five types of chemical reactions we will talk about:

1. Combination (Synthesis) reactions

2. Decomposition (Analysis) reactions

3. Single displacement (Substitution)reactions

4. Double displacement (Metathesis) reactions

5. Combustion reactions

You need to be able to identify the type of reaction and

predict the product(s)


1. Synthesis reactions

• Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)

reactant + reactant 1product


1. Synthesis reactions

Basically: A + B AB

Example:

2H2 (g)+ O2 (g) 2H2O (l)

C (s)+ O2(g) CO2 (g)


Combination Reaction

• Metal + Oxygen → Metal Oxide

Example:

2Mg (s) + O2 (g) → 2MgO (s)

4Na (s) + O2 (g)→ 2Na2O (s)

• Non-Metal + Oxygen → Acidic Oxide/Acidic Anhydride

Example:

S (s) + O2 (g) → SO2 (g)

C(s) + O2 (g) → CO2 (g)


Combination Reaction

• Non-Metal Oxide + Water → Acid

Example:

SO2 (g) + H2O (l)→ H2SO3 (aq)

CO2 (g) + H2O (l) → H2CO3 (aq)

• Metal Oxide + Water → Alkali/Base

Na2O (s) + H2O (l) → 2NaOH (aq)

MgO (s) + H2O (l) → Mg(OH)2 (aq)


Synthesis Reactions

Here is

another

example of

a synthesis

reaction


Practice

Predict the products. Write and balance the following

synthesis reaction equations.

• Sodium metal reacts with chlorine gas

Na(s) + Cl2(g)

• Solid Magnesium reacts with fluorine gas

Mg(s) + F2(g)

• Aluminum metal reacts with fluorine gas

Al(s) + F2(g)


2. Decomposition Reactions

• Decomposition reactions occur when a compound

breaks up into the elements or in a few to simpler

compounds

1 Reactant Product + Product


2. Decomposition Reactions

In general: AB A + B

Example:

2 H2O 2H2 + O2

2 HgO 2Hg + O2


Decomposition Reactions

• Metal Oxide Metal + Oxygen gas


2HgO (s) 2Hg (l) + O2 (g)

Metal Carbonates Metal Oxide + CO2

Na2CO3 (s) Na2O (s) + CO2 (g)

CaCO3 (s) CaO (s) + CO2 (g)


• Metal Nitrates Metal Nitrites + Oxygen gas


NaNO3 (s) NaNO2 (s) + O2 (g)

Metal Bicarbonates Metal Carbonate + H2O + CO2

2NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g)

Metal Oxyhalides Metal Halide + O2 (g)

2KBrO3 (s) 2KBr (s) + 3O2 (g) 322 // OFeMnO


• Another view of a decomposition reaction:


Practice

Predict the products. Then, write and balance

the following decomposition reaction

equations:

1. Solid Lead (IV) oxide decomposes

PbO2(s)

2. Aluminum nitride decomposes

AlN(s)


Practice

Identify the type of reaction for each of the following

synthesis or decomposition reactions, and write the

balanced equation:

• N2(g) + O2(g) Nitrogen Monoxide

• BaCO3(s)

• Co(s)+ S(s) (make Co be +3)

• NH3(g) + H2CO3(aq)

• NI3(s)


3. Single Replacement Reactions

• Single Replacement Reactions occur when one element replaces another in a compound.

• A metal can replace a metal (+)

OR

• Nonmetal can replace a nonmetal (-).


3. Single Replacement Reactions

element + compound product + product

A + BC AC + B (if A is a metal)

OR

A + BC BA + C (if A is a nonmetal)

(remember the cation always goes first!)

When H2O splits into ions, it splits into

H+ and OH- (not H+ and O-2 !!)


Activity Series

• Metals

Li, K, Ba, Ca, Na, Mg, Al, Zn, Cr, Fe, Cd, Co, Ni, Pb, H, Cu, Hg, Ag, Pt, Au

arranged in decreasing activity

• Non-Metals

F2, Cl2, Br2, I2


Single Replacement Reactions

• Another view:



Write and balance the following single replacement reaction equation:

• Zinc metal reacts with aqueous hydrochloric acid

Zn(s) + 2HCl(aq) ZnCl2 + H2(g)

Note: Zinc replaces the hydrogen ion in the reaction



• Sodium chloride solid reacts with fluorine gas

2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)

Note that fluorine replaces chlorine in the compound

• Sodium fluoride reacts with chlorine gas

NaF(s) + Cl2(g) (no chemical reaction)

• Aluminum metal reacts with aqueous copper (II) nitrate

Al(s)+ Cu(NO3)2(aq)


4. Double Replacement Reactions

• Double Replacement Reactions occur when a metal

replaces a metal in a compound and a nonmetal replaces

a nonmetal in a compound

Compound + compound product + product

AB + CD AD + CB


Double Replacement Reactions

Think about it like “foil”ing in algebra, first and last ions

go together + inside ions go together

Example:

AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)

K2SO4(aq) + Ba(NO3)2(aq) 2KNO3(aq) + BaSO4(s)


Practice

Predict the products and balance the following

chemical reactions

1. HCl(aq) + AgNO3(aq)

2. CaCl2(aq) + Na3PO4(aq)

3. Pb(NO3)2(aq) + BaCl2(aq)

4. FeCl3(aq) + NaOH(aq)

5. H2SO4(aq) + NaOH(aq)

6. KOH(aq) + CuSO4(aq)


5. Combustion Reactions

• Combustion reactions occur when a hydrocarbon reacts with oxygen gas.

• This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)


Combustion Reactions

• In general:

CxHy + O2 CO2 + H2O

• Products in combustion are

ALWAYS carbon dioxide and

water. (although incomplete

burning does cause some by-

products like carbon monoxide)

• Combustion is used to heat homes

and run automobiles (octane, as in

gasoline, is C8H18)


Combustion

Reactions


Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

Combustion

• Example

• C5H12 + 8O2 5CO2 + 6H2O

• Write the products and balance the following

combustion reaction:

• C10H22 + O2


Mixed Practice

State the type, predict the products, and

balance the following reactions:

1. BaCl2 + H2SO4

2. C6H12 + O2

3. Zn + CuSO4

4. Cs + Br2

5. FeCO3


Balancing Chemical Equation


Because of the principle of the

conservation of matter,

an equation must be balanced.

It must have the same

number of atoms of the

same kind on both sides.

Lavoisier, 1788

Balancing Equations

– When balancing a chemical reaction

you may add coefficients in front of the

compounds to balance the reaction, but

you must not change the subscripts.

– Changing the subscripts changes the

compound. Subscripts are determined

by the valence electrons (charges for

ionic or sharing for covalent)

Balancing Chemical Equations

1. Write the correct formula(s) for the reactants on the left side and the correct formula(s) for the product(s) on the right side of the equation.

Ethane reacts with oxygen to form carbon dioxide and water

C2H6 + O2 CO2 + H2O


C2H6 + O2 CO2 + H2O

2. Change the numbers in front of the formulas (coefficients) to make the number of atoms of each element the same on both sides of the equation. Do not change the subscripts.

2C2H6 NOT C4H12


3. Start by balancing those elements that appear in only one reactant and one product.

C2H6 + O2 CO2 + H2O start with C or H but not O

2 carbon on left

1 carbon on right

multiply CO2 by 2

C2H6 + O2 2CO2 + H2O

6 hydrogen on left

2 hydrogen on right

multiply H2O by 3

C2H6 + O2 2CO2 + 3H2O


4. Balance those elements that appear in two or more reactants or products.

2 oxygen on left

4 oxygen (2x2)

C2H6 + O2 2CO2 + 3H2O

+ 3 oxygen (3x1)

multiply O2 by 7/2

= 7 oxygen on right

C2H6 + 7/2O2 2CO2 + 3H2O remove fraction multiply both sides by 2

2C2H6 + 7O2 4CO2 + 6H2O


5. Check to make sure that you have the same number of each type of atom on both sides of the equation.

2C2H6 + 7O2 4CO2 + 6H2O

Reactants Products

4 C

12 H

14 O

4 C

12 H

14 O

4 C (2 x 2) 4 C

12 H (2 x 6) 12 H (6 x 2)

14 O (7 x 2) 14 O (4 x 2 + 6)

Example 1

Balance the chemical reaction

AlCl3 + H2 → HCl + Al


REACTANT PRODUCT

Al 1 1 Cl 3 1 H 2 1

NOT BALANCE

3

3

3

3

6

6

2 2

6

2 2 6

6

BALANCED

Example 2

Balance the following chemical equation

Al2(SO4)3 + Ca(OH)2 → Al(OH)3 + CaSO4


REACTANT PRODUCT

Al : 2 1

Ca: 1 1

S : 3 x 1 = 3 1

H : 2 x 1 = 2 3 x 1 = 3

O : (3x4)+ (2x1) =14 (3x1) + 4 = 7

NOT BALANCE

2

2

6

[2 ]

2 ( )

10

3

3

3 ( ) 6

[3 ] 18

3

3

( x 3 ) 18

3

BALANCED

Exercises

Balance the following chemical equation

1. C2H6 + O2 → CO2 + H2O

2. P4 + O2 → P2O5

3. Ag + S8 → Ag2S

4. AlI3 + HgCl2 → AlCl3 + HgI2

5. AgNO3 + K3PO4 → Ag3PO4 + KNO3

6. KClO3 → KCl + O2


CHEMICAL REACTION - WordPress.com · 09/08/2013 · Chemical Equation •A chemical ... Products...

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