Charles’ Law at a glance Easy Kemistry. 🧪📘

 CHARLES’ LAW

Charles’ law states that the volume of a fixed mass of gas at constant pressure is directly proportional to its temperature in the Kelvin scale.

This means that:

• When temperature increases, volume increases

• When temperature decreases, volume decreases

Mathematically,

                         V α T

                         V = k/T

                                        V   = k
                                        T

Hence,             V₁ = V₂

                         T₁   T₂

where
(V) = volume of the gas
(T) = absolute temperature (in Kelvin)

The graphical representation of Charles’ law is as shown below:

 

 

 

 

 

 

 

 

 

EXPLANATION OF CHARLES’ LAW USING THE KINETIC THEORY

When a gas is heated, (at constant pressure) its particles gain energy and move faster, pushing the walls of the container outward (to maintain the same number of collisions on the walls of container) so the volume increases. When the gas is cooled, the particles move more slowly and the volume decreases.

Examples

• A balloon expands when heated and shrinks when cooled.

• Hot air causes a hot-air balloon to rise because the air expands.

Conclusion

Charles’ Law shows how the volume of a gas changes with temperature at constant pressure.

Examples of calculation based on Charles law

A certain mass of a gas occupies 300cm³ at 35^oC. At what temperature will it have its volume reduced by half assuming its pressure remains constant?

       Solution:

       V₁ = 300cm³, T₁ = 35^oC = (35 + 273)K = 308K, V₂ = V₁/2 = 300/2 = 150cm³, T₂ = ?

       Using the formula for Charles’ law

                     V₁ = V₂
                      T₁    T₂

       T₂ = V₂T₁ = 150cm³ x 308K = 154K
                  V₁              300cm³

     

EASY KEMISTRY

CHEMISTRY TEST – CHARLES’ LAW
Time: 30 Minutes

Name: __________________________ Class: __________ Date: __________

Choose the correct option from A–D

1. Charles’ law states that for a fixed mass of gas at constant pressure,
A. volume is inversely proportional to temperature
B. volume is directly proportional to temperature
C. pressure is proportional to temperature
D. pressure is inversely proportional to volume

2. Which of the following must remain constant for Charles’ law to apply?
A. Volume
B. Pressure
C. Temperature
D. Mass and volume

3. The temperature used in Charles’ law calculations must be in
A. degrees Celsius
B. degrees Fahrenheit
C. Kelvin
D. Centigrade

4. If the temperature of a gas is increased, its volume will
A. decrease
B. remains constant
C. increase
D. become zero

5. The mathematical expression for Charles’ law is
A. PV = k

B.  V = k 
      T

C.  PV= k 

D.  V = k 
      T

6. A gas has a volume of 200 cm³ at 300 K. What will be its volume at 600 K?
A. 100 cm³
B. 200 cm³
C. 300 cm³
D. 400 cm³

7. Which of the following is an application of Charles’ law?
A. Thermometer
B. Hot-air balloon
C. Barometer
D. Syringe

8. When a gas is cooled, its volume
A. increases
B. decreases
C. remains the same
D. doubles

9. A gas occupies 150 cm³ at 300 K. What will be its volume at 600 K?
A. 75 cm³
B. 100 cm³
C. 300 cm³
D. 450 cm³

10. Charles’ law is valid only when
A. pressure is constant
B. volume is constant
C. temperature is constant
D. mass is constant

11. A gas occupies 50 cm³ at 250 K. What will be its volume at 500 K?
A. 25 cm³
B. 50 cm³
C. 75 cm³
D. 100 cm³

12. According to Charles’ law, volume is directly proportional to
A. pressure
B. temperature
C. mass
D. density

13. What happens to the volume of a gas if its temperature is halved?
A. It doubles
B. It halves
C. It remains constant
D. It becomes zero

14. A gas has a volume of 300 cm³ at 300 K. Find its volume at 150 K.
A. 150 cm³
B. 200 cm³
C. 300 cm³
D. 450 cm³

15. The temperature 0°C is equal to
A. 100 K
B. 273 K
C. 373 K
D. 0 K

16. Which of the following instruments shows the effect of Charles’ law?
A. Syringe
B. Thermometer
C. Hot-air balloon
D. Barometer

17. If a gas expands, its temperature must have
A. decreased
B. increased
C. remained constant
D. become zero

18. A gas has a volume of 120 cm³ at 300 K. What will be its volume at 600 K?
A. 60 cm³
B. 120 cm³
C. 180 cm³
D. 240 cm³

19. Charles’ law applies only to

A. solids
B. liquids
C. gases
D. metals

20. When the temperature of a gas is reduced to zero Kelvin, its volume becomes

A. maximum
B. constant
C. minimum
D. zero

THEORY QUESTIONS  

1.  (a) State Charles’ law.
     (b) Define the terms volume and absolute temperature as used in the law.

................................................................................................................................

2.    Explain why the volume of a gas increases when it is heated at constant pressure.

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3.    A gas has a volume of 200 cm³ at 300 K. Calculate its volume at 600 K, assuming the pressure remains constant.

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4. (a) Why must temperature be measured in Kelvin when using Charles’ law?
    (b) What would happen if Celsius were used instead?

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5.    State two everyday applications of Charles’ law and explain one of them.

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Balancing Chemical Reactions at a glance

 

Balancing Chemical Reactions

A chemical equation shows how substances react to form new substances.
A balanced chemical equation has the same number of each type of atom on both sides of the equation.

This is based on the Law of Conservation of Mass, which states that matter is neither created nor destroyed in a chemical reaction.

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Steps for Balancing Chemical Equations

1. Write the correct chemical formula for all reactants and products.

2. Count the number of each atom on both sides.

3. Adjust the coefficients (numbers in front of formulas) to make the atoms equal.

4. Do not change subscripts in the formulas.

5. Check that all atoms are balanced.

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Examples

1. Formation of Water

Unbalanced:
H₂ + O₂ → H₂O

Balanced:
2H₂ + O₂ → 2H₂O

2. Formation of Magnesium Oxide

Unbalanced:
Mg + O₂ → MgO

Balanced:
2Mg + O₂ → 2MgO

3. Reaction of Hydrogen and Chlorine

Unbalanced:
H₂ + Cl₂ → HCl

Balanced:
H₂ + Cl₂ → 2HCl

4. Combustion of Methane

Unbalanced:
CH₄ + O₂ → CO₂ + H₂O

Balanced:
CH₄ + 2O₂ → CO₂ + 2H₂O

5. Reaction of Zinc with Hydrochloric Acid

Unbalanced:
Zn + HCl → ZnCl₂ + H₂

Balanced:
Zn + 2HCl → ZnCl₂ + H₂

Conclusion

Balancing chemical equations ensures that the number of atoms on both sides is equal, showing that mass is conserved in chemical reactions.

EASYKEMISTRY

Chemistry Test – Balancing Chemical Equations
Time: 30 Minutes

Name: __________________________ Class: __________ Date: __________

SECTION A – Balance the following equations

(Each question carries 2 marks)

1.     H₂ + N₂ → NH₃

2.     Fe + H₂O → Fe₃O₄ + H₂

3.     Na + H₂O → NaOH + H₂

4.     Al + O₂ → Al₂O₃

5.     CaCO₃ → CaO + CO₂

6.     KClO₃ → KCl + O₂

7.     Zn + HNO₃ → Zn(NO₃)₂ + H₂

8.     C₂H₆ + O₂ → CO₂ + H₂O

9.     Pb(NO₃)₂ → PbO + NO₂ + O₂

10.     Cu + HNO₃ → Cu(NO₃)₂ + NO₂ + H₂O

SECTION B – Answer all questions

1.      What is meant by a balanced chemical equation?

    

...................................................................................................................................................

 

2.      State the law that is obeyed when chemical equations are balanced.

......................................................................................................................................................

3.     Why is it important to balance chemical equations

...........................................................................................................................................................

4.     Why should subscripts not be changed when balancing equations?

...............................................................................................................................................................

5. Write a balanced chemical equation for the reaction between magnesium and dilute hydrochloric acid.

.........................................................................................................................................

END OF TEST

STATES OF MATTER

Matter can exist in three states,  that is, solid, liquid and gaseous The fundermental difference between these three is the forces of attraction (cohesive forces) between the particles, 

SOLID( strong cohesive forces)	LIQUID(weak cohesive forces)	GASES
Have definite shape and volume	Have no definite shape but definite volume	Have no definite shape and volume
Very dense	Less dense	Least dense
Incompressible	cannot be compressed	Compressible
Fixed mass	Substances have a fixed mass	Fixed mass
Particle vibrate and rotate about a fixed point	Particles can vibrate as well as  move about within a restricted space	Particles move about constantly at great speed and at random

      

CHANGE OF STATE

MELTING

Melting is the physical process where a substance changes from a solid to a liquid. When a solid is heated, the particles acquire greater kinetic energy and move violently. A point is reached when the forces of vibration overcome the cohesive forces holding the solid particles together and the crystalline structure collapses. The particles are no longer held in fixed positions but are free to move about and the liquid state is reached. The temperature at which this occurs is called the melting point of the solid.

 

BOILING

When a liquid is heated, the rate of evaporation increases and the value of the saturated vapour pressure equal the prevailing atmospheric pressure. When this happens, the liquid is said to boil and the temperature at which this happen is known as the boiling point of the liquid.

The boiling point of a liquid change with change in atmospheric pressure. If the pressure is raised, the boiling point will increase and if the pressure is lowered the boiling point will decrease. Also, the presence of impurities increases the boiling point of a liquid.

EVAPORATION

Evaporation is the process of vapourization of liquids at all temperatures. When the surface of a liquid is exposed, the molecules near the surface of the liquid will acquire extra kinetic energy, large enough to enable them break away from the cohesive force binding them to the neighbouring particles. Once free, they escape from the liquid surface to become molecules in the vapour state.

 

Evaporation results in decrease in the volume of liquid and lowering the temperature of the liquid, therefore it causes cooling. Also, it occurs at all temperature but increases with increase in temperature. In addition, it is slower in electrovalent liquids than in covalent liquids.

 

DIFFERENCES BETWWEEN EVAPORATION AND BOILING

EVAPORATION	BOILING
Takes place at the surface of the liquid	Involves the entire volume of the liquid
Takes place at all temperature	Takes place at a fixed temperature

 

CONDENSATION AND FREEZING

Condensation is a process whereby a vapour loses some of its kinetic energy to a colder body and changes into the liquid state.

When a liquid cools, it loses heat energy to its surroundings, causing its temperature to drop. If the cooling continues, the temperature of the liquid keeps dropping until it reaches the freezing point of the liquid. At this temperature, the liquid changes into solid.

 

EVALUATION

1.     Describe the melting process of a solid.

2.     State two differences between evaporation and boiling.

 

KINETIC THEORY OF GASES

The theorypostulates the following for an ideal or perfect gas:

Gas molecules are in constant, rapid, straight motion, colliding with one another and with the walls of the container.

 

The collision of gas molecules is perfectly elastic.

The total volume of the gas molecule is negligible compared to the volume of the container.

The force of attraction between the gas molecules is negligible.

The average kinetic energy of the molecule is a measure of the temperature of the gas molecules.

 

PHENOMENA SUPPORTING THE KINETIC THEORY OF GASES

Brownian motion: This is the constant, irregular movement of particles in a liquid or gas. It shows that gas molecules are in constant motion.

Diffusion: Diffusion is the movement of particles from a region of higher concentration to lower concentration. Diffusion is common in gases and it results from the random movement of particles of a gas.

 

Electrolysis note for students

  IONIC THEORY

Ionic theory as proposed by Arrhenius states that when an ionic compound is dissolved in water or melted, some or all its particles dissociate (break up) into free moving charged particles called ions. This dissociation into ions is called ionization.

These free ions move randomly in all directions inside the solution. as seen in fig. A

But the ions lose their freedom as soon as an electric current is passed through the solution and they become orderly, surrounding themselves around the opposite pole or electrode as they begin to pull electrons from the electrodes or lose electrons to the electrodes and come out of the solution.

 Electrolysis is defined as the chemical decomposition of a compound by the passage of electricity through the solution of the compound or its molten form.

Terms commonly used in Electrolysis 

i. ELECTROLYTE: An electrolyte is a compound which allows the passage of electricity through its solution or its molten state and is decomposed in the process. 

Examples of electrolytes include dilute Acids and Alkalis and all electrovalent compounds like NaCl.

 Electrolytes are grouped in two

 1. Strong Electrolytes: These are compounds which ionize completely in solutions.

They usually have large amounts of ions in solution and hence are good conductors. Examples are all sodium and potassium salts, minerals acids, and caustic alkalis.

      NaCl_(aq) →Na⁺_(aq)  +  Cl-_(aq)

Weak Electrolytes: These are compounds that ionize partially in solution

 There is slight dissociation of the ions in dilute solutions, and so they contain less ions in solution. Examples include organic acids, aqueous ammonia, etc.

   CH₃COOH_(aq) →CH₃COO-_(aq) + H⁺(_(aq)

 Non-Electrolytes: These are compounds which do not conduct electricity at all, whether molten or in solution 

 Non-electrolytes are mostly covalent compounds and only exist as molecules. Examples include vegetable oils, organic solvents like alcohols, benzene sugar solution 

  Conductor and Non-conductor

  Conductors:  These are metals which allow the passage of electricity through them.

 Examples include all metals in general Silver is the best conductor followed by copper and ionic solutions

 Non-conductor (Insulators): These are substances that do not conduct or allow electricity to pass through them.  Examples include wood, paper, air, rubber, plastic.

  Electrodes: these are wires rods or plates through which an electric current enters or leaves the electrolytes

2.  Anodes:  This is the positive electrode through which electrons leave electrolytes. It is  the electrode where oxidation occurs

 3. Cathode: This is the negative electrode through which electrons enter the electrolyte. It is also the electrode where reduction takes place

 4.  Cations: - these are positively charged ions. They migrate to the cathode (negative electrode) during electrolysis.

5.  Anions: these are negatively charged ions. They migrate to the anode (positive electrode) during electrolysis.

5. Electrolytic Cell: This is a vessel or container containing two electrons connected to a battery and an electrolyte. It is used for Electrolysis.

When electrolysis is carried out on the solution of an ionic compound. There are usually two cations and two anions which  migrate to the cathode and anode respectively but only one of each ion is  preferentially discharged at the electrodes.

The following factors determine which ion gets discharged at each electrode.

1. Position of ions in the electrochemical series.

The ions at the bottom of the series for the positive ions are preferentially discharged to the ions at the top of the series, for example for a solution of sodium chloride containing Na⁺ and Cl^-, H⁺ and OH^- hydrogen is below sodium in the series and so will be preferentially discharged. For non-metals the less electronegative element is preferentially discharged to the more electronegative. So OH^- is preferentially discharged to Cl^-

2. Concentration of ion in the electrolyte. For a concentrated solution of a salt, the more concentrated ion is preferentially discharged to the less concentrated ion. but concentration does not matter where there is a large gap between the two ions in the series.

3. Nature of the electrodes: - Electrodes that have affinity for certain ions will cause those ions to be preferentially discharged during electrolysis. But both Platinum and Carbon are two electrodes that are considered as neutral or passive electrodes since they have no affinity for any element. 

 Examples of Electrolysis

1. Electrolysis of Acidified Water (water containing drops of H₂SO₄)

                
The Hoffman Voltameter is used; both the anode and cathode are platinum foil. 

The ions present in the electrolyte are:

          Cations          Anions

H₂SO₄ → 2H⁺_(g)    +       SO₄^2-            

H₂O →       H⁺_(aq)    +   OH^-_(aq)

At the Cathode: H⁺ ion migrate to the cathode and take up electrons to form neutral hydrogen atoms.

H+_(aq)  + e-→ H(g)

The hydrogen atoms then combine to form hydrogen gas molecule

H_(g) + H_(g)→ H_2(g) 

 Overall equation

2H⁺_(aq)  +  2e^- →H_2(g)

 At the anode: Both SO₄^2- and OH^- ions migrate to the anode where OH^- ions being lower in the electrochemical series is preferentially discharged and lose its electrons to the anode to become a neutral - OH group.

OH^-_(aq) → OH  + e

The neutral –OH group combines in pairs to form one molecule of water and one atom of oxygen.

OH  +  OH → H₂O_(l)  +  O_(g)

The oxygen atoms then combine with another free oxygen atom to form an oxygen gas molecule.

O_(g) + O_(g)→O_2(g)        

Overall equation

 4OH^-_(aq)→2H₂O_(l)  +  O_2(g) +  4e^-

 Note: At the end of the electrolysis the solution becomes more concentrated or more acidic as the components of water (H₂ and O)

H+(aq)  + e–→ H_(g)

The hydrogen atoms then combine in pairs to form diatomic hydrogen gas molecule 

H_(g) + H_(g)→H_2(g).

Overall equation

2H⁺_(aq)  +  2e^-→ H_2(g)

Thus, hydrogen gas is obtained at the cathode.

At the anode: both Cl- and OH^- ions migrate to the anode where Cl^- ions are preferentially discharged. This is because it is  higher in concentration than OH^- ion and the two ions are close to each other in the series.  

      Cl^-_(aq)→Cl_(g)  +  e^- 

 The chlorine atoms combine to give the molecules. 

       Cl_(g)  +  Cl_(g)→Cl₂

Overall equation

2Cl^-_(aq)→ Cl_2(g)  +   2e^-

Chlorine gas is obtained at the anode.

 

3.Electrolysis Of Copper (II) Tetraoxosulphate (VI) Solution Using Different  Anode: 

1. With carbon or platinum electrodes.

               Cations            Anions

CuSO₄  →    Cu²⁺_(g)    +    SO₄^2-_(aq)   

H₂O      →     H⁺_(aq)    +     OH^-_(aq)

At the Cathode: Cu²⁺ and H⁺ ion migrate to the cathode where Cu²⁺ being lower than and less electropositive than H⁺ is preferentially discharged  as metallic copper on the cathode.

 Cu²⁺_(aq)  + 2e^-→ Cu_(s)

 

At the anode: SO₄^2- and OH^- ions migrate to the anode where OH^- ions lose their electrons to become a neutral  - OH group.

OH^-_(aq) → OH  + e^-

OH  +  OH → H₂O_(l)  +  O_(g)

O_(g) + O_(g)→O_2(g)        

 Overall equation

4OH^-_(aq) →2H₂O_(l) + O_2(g) + 4e-

Electrolysis of CuSO₄ using different electrodes

1. Using Pt. or C- electrodes: - Pt. and C-electrodes as we know are inert or passive electrodes and do not determine the product of the electrolysis

Uses Of Electrolysis 

1. Extraction of metals like Na, K, Mg, Ca and Al.

2. Purification of metals copper, 

3. Electroplating

4. Preparation of some elements like Cl₂ as sodium hydroxide, hydrogen and chlorine from electrolysis of brine using cathode.

 

OBJECTIVE QUESTIONS

1. Electrolysis is the process of

(a) producing electricity from chemicals
(b) using electricity to cause chemical change
(c) breaking compounds by heating
(d) mixing acids and bases

2. The substance that is decomposed during electrolysis is called the
(a) electrode
(b) electrolyte
(c) conductor
(d) catalyst

3. Which of the following is NOT an electrolyte?
(a) Molten sodium chloride
(b) Dilute sulphuric acid
(c) Distilled water
(d) Sodium hydroxide solution

4. In electrolysis, oxidation occurs at the
(a) cathode
(b) anode
(c) electrolyte
(d) battery

5. Reduction takes place at the
(a) anode
(b) cathode
(c) electrolyte
(d) circuit

6. The positive electrode in an electrolytic cell is the
(a) cathode
(b) anode
(c) electrolyte
(d) salt bridge

7. Which particle moves to the cathode during electrolysis?
(a) Anion
(b) Cation
(c) Electron
(d) Neutron

8. During the electrolysis of molten sodium chloride, the product at the cathode is
(a) chlorine gas
(b) sodium metal
(c) hydrogen gas
(d) oxygen gas

9. During electrolysis of acidified water, the gas collected at the anode is
(a) hydrogen
(b) oxygen
(c) chlorine
(d) nitrogen

10. Which of the following statements is correct?
(a) Oxidation occurs at the cathode
(b) Reduction occurs at the anode
(c) Anions move to the anode
(d) Cations move to the anode

11. A substance that allows electric current to pass through it by movement of ions is called a
(a) conductor
(b) semiconductor
(c) electrolyte
(d) insulator

12. The electrodes used in electrolysis may be
(a) active or inert
(b) solid or liquid
(c) metals only
(d) non-metals only

13. Which of the following is an example of an inert electrode?
(a) Zinc
(b) Copper
(c) Platinum
(d) Iron

14. The process of coating an object with a thin layer of metal using electricity is called
(a) electrolysis
(b) electroplating
(c) electrolysis reaction
(d) electrorefining

15. In the electrolysis of copper(II) sulphate using copper electrodes, the anode
(a) dissolves
(b) gains mass
(c) remains unchanged
(d) produces hydrogen

16. Which law of electrolysis states that the mass of a substance deposited is proportional to the quantity of electricity passed?
(a) Ohm’s law
(b) Faraday’s first law
(c) Boyle’s law
(d) Charles’ law

17. The electrolyte in a dry cell is usually
(a) sodium chloride
(b) potassium hydroxide
(c) ammonium chloride paste
(d) sulphuric acid

18. In electrolysis, electrons flow through the
(a) electrolyte
(b) external circuit
(c) electrode
(d) salt solution

19. Which of the following products is obtained at the cathode during electrolysis of dilute sulphuric acid?
(a) Oxygen
(b) Hydrogen
(c) Chlorine
(d) Sulphur

20. The main purpose of electrorefining is to
(a) produce alloys
(b) extract metals from ores
(c) purify metals
(d) coat metals

ALKENES at a glance

 ALKENES

Alkenes are a homologous series of unsaturated hydrocarbons with a general molecular formular C_nH_2n.

They are named by replacing the ending "ane" of the corresponding alkane with "ene" for each member of the series.

NOTE: because alkenes contain double bonds between carbon to carbon i.e C=C n=1 does not exist.

When n=	General Molecular Formulae CnH2	Name
2.	C2H2x2= C2H4	Ethene
3.	C3H2x3 = C3H6	Propene
4.	C4H2x4 = C4H8	Butene
5.	C5H2x5 = C5H10	Pentene
6.	C6H2x6 = C6H12	Hexene
7.	C7H2x7 = C7H14	Heptene
8.	C8H2x8 = C8H16	Octene
9.	C9H2x9 = C9H18	Nonem
10.	C10H2x10 = C10H20	Decene

 

NOMENCLATURE OF ALKENES

When naming the alkenes, care must be taken because unlike the alkanes which have only single bonds, the alkenes contain double bonds, and so the naming of the substituents is based on the position of the double bond. For example, the molecule CH₃CH=CHCH₃ is named but-2-ene.

Although the double bond joins carbon atoms 2 and 3, the number 2 is used because it gives the lowest number to the double bond.

other examples include 

(i)  CH₃-CH₂-CH₂-CH=CH₂           

        Pent-1-ene or Pentene

(ii) CH₃CH₂CH=CHCH

        Pent-2-ene

                     

                    CH₃
                     |
(iii)       CH₃C=CHCH₃                    

         2-methylbut-2-ene

                          CH₃

                           |

(iv)       CH₃-C=C-CH₃
                       |   

                       CH₃  

       2,3-dimethylbut-2-ene

                    CH₃         
                          |   
           CH₃CH₂C=CCH₂CH₃                                      
                               |

                              CH₃

         3,4-dimethylhex-3-ene

             CH₃            CH₃

                |                   |

(vi)   CH₃C-CH=CH-C-CH₃
                 |                  |      
                CH₃            CH₃

    2,2,5,5-tetramethylhex-3-ene

MOLECULAR STRUCTURES OF ALKENES

	ALKENES molecular formula /name	STRUCTURAL FORMULAR	Condensed  FORMULAR
2.	C2H4 Ethene	H             H            ∖         ∕              C=C          ∕         ∖       H           H	H2C=CH2
3.	C3H6 Propene	H    H     H            |      |         ∕  H — C — C=C            |       |        ∖           H     H       H	CH3CH=CH2
4.	C4H8 Butene	H H H   H         |   |   |      ∕    H-C-C-C=C         |   |   |       ∖         H H H      H	CH3CH2CH=CH2
5.	C5H10 Pentene	H H H  H        H        |   |   |    |       ∕   H-C-C-C-C=C        |   |   |   |       ∖       H H H H        H	CH3(CH2)2CH=CH2
6.	C6H12 Hexene	H H H H  H     H        |   |   |   |    |       ∕   H-C-C-C-C-C=C         |   |   |   |   |     ∖        H H H H H      H	CH3(CH2)3CH=CH2
7.	C7H14 Heptene	H H H H H H       H       |   |    |   |   |   |       ∕  H-C-C-C-C-C-C=C       |    |   |   |   |   |       ∖      H H H H H H        H	CH3(CH2)4CH=CH2
8.	C8H16 Octene	H H H H H H  H     H        |   |    |   |   |   |   |      ∕  H-C-C-C-C-C-C-C=C        |  |    |   |   |   |   |      ∖       H H H H H H H      H	CH3(CH2)5CH=CH2
9.	C9H18 Nonene	H H H H H H H  H     H       |   |   |    |   |   |    |   |      ∕                          H-C-C-C-C-C-C-C-C=C       |   |   |   |    |   |   |   |     ∖        H H H H H H H H   H	CH3(CH2)6CH=CH2
10.	C10H20 Decene	H H H H H H H H  H     H      |  |    |    |    |  |    |   |   |     ∕ H-C-C-C-C-C-C-C-C-C=C      |   |   |    |   |   |  |   |    |     ∖           H H H H H H H H H      H	CH3(CH2)7CH=CH2

LABORATORY PREPARATION OF ETHENE

Ethene is prepared in the laboratory by dehydration of alkanols such as ethanol (C₂H₅OH) by concentrated H₂SO_4.

DIAG.

                                                     Laboratory preparation of Ethene

equation for the reaction

step i:      C₂H₅OH + H₂SO₄ → C₂H₅HSO₄ + H₂O.

  step ii.   C₂H₅HSO₄ →C₂H₄ + H₂SO₄

When ethylhydrogentetraoxosulphate (VI) is heated, it releases ethene which is collected over water.

 

NOTE: The wash bottle containing sodium hydroxide is to remove Sulphur (iv)oxide.

PHYSICAL PROPERTIES OF ETHENE (ALKENES)

1. It is colourless and odourless gas

2. It is neutral litmus paper

3. It is almost insoluble in water

4. It is less dense than air.

Chemical Properties Of Ethene

Alkenes such as ethene undergoes addition reaction 

1. Reaction of ethene with hydrogen in the presence of nickel as a catalyst

                                  Ni    
          H₂C=CH₂ + H₂ →   CH₃CH₃         
              ethene                   ethane

This reaction is important in the conversion of oil into margarine by the process known as HYDROGENATION.

2. Reaction of ethene with chlorine to produce 1,2-dichloroethane.

 CH₂=CH₂ + Cl₂ → ClCH₂-CH₂Cl

3. Reaction of ethene with bromine to produce 1,2-dibromoethane

 CH₂=CH₂ + Br₂ → CH₂Br-CH₂Br

4. Reaction of ethene with oxygen or combustion reaction of ethene (alkenes) to produce carbon(iv)oxide and water

  CH₂=CH₂ + 3O₂ →2CO₂ + 2H₂O

5. Reaction of ethene with hydrogen halide (Hydrogen chloride) (HCl) to produce ethylchloride.

 CH₂=CH₂ + HCl → CH₃CH₂Cl  

6. Reaction of ethene with water in the presence of dilute H₂SO₄ to produce ethanol

   CH₂=CH₂ + H₂O →CH₃CH₂OH

7. Reaction of ethene with neutral KMnO₄ to produce 1,2-ethan-diol (glycol)

 CH₂=CH₂ + KMnO₄ → CH₂—CH₂
                                            |          |
                                           OH     OH    

                                     ethan-1,2-diol

 KMnO4 is decolorized in the above reaction, and this reaction distinguishes alkenes from alkanes which do not decolorize KMnO₄

Uses Of Ethene

1. In the production of polythene which is used for making nylon or polythene bags and wrappers

2. In the manufacturing of margarine by the process of hydrogenation.

 Other examples of alkenes are as follows

(i)      CH₃CH₂C = CCH₃                                           (ii)     CH₃C = CHCH₃
                                 |       |                                                                   |
                           CH₃ CH₃                                                            CH₃
            

             2,3-dimethylpent-2-ene                                  3-methylbut-2-ene

                       CH₃                                                                                                CH₃ 
                        |                                                                                                      |    
(iii)       CH₂= C — CH—CH₂CH₂CH=CH₂        (iv)        CH₃CH₂CHCH=CHCH=C=CH₂ 
                                |                                                                            |
                                CH₂CH₃                                                              CH₂CH₃  
         

              2-methyl, 3-ethylhept-1,6-diene                                6-ethyl, 3-methyloct-1,2,4-triene

                                                                                    Cl
                                                                                     |
(v)       CH₃CH=CHCH₃                        (vi)      CH₃-C-CH=CH₂ 
                            |                                                         |
                           Cl                                                      Cl
            3-chlorobut-2-ene                               3,3-dichlorobut-1-ene

(vii)     CH₃CH₂C=CH=CHCH₃              (viii)     CH₃C=CHC=CH₃  
                           |            |                                              |           |
                          Cl         Br                                           Cl        Cl
            2-bromo, 4-chlorohex-2,3-diene        2,4-dichloropent-1,3-diene

                           

                                 Cl                                                                   Cl
                                  |                                                                       |
(ix)      CH₂=C=CH-C=C-CH₃                         (x)     CH₃CHCH=C-CH₃  
                                       |                                                    |             |
                                      Br                                                 Cl         Cl

                5-bromo,3-chlorohex-1,2,4-triene                 4,2,2-trichloropent-2-ene

              

          H H H            H                                                        CH₂CH₃
               |    |  |            ∕                                                          ∕
(xi)  H-C-C-C-C=C                              (xii)   CH₃CH = C
             |    |   |   |      ∖                                                        ∖                                     
            H H   | H        H                                                       CH₂CH₂Cl
                      |                                                                     5-chloro -3-ethylpent-2-ene
                 H-C-H                                              
                      |
                     H                                                                       
       3-methylpent-1-ene

                       

                                    CH₃
(xiii)                          ∕
            H₂C = C = C
                                 ∖
                                   H
            But-1,2-diene 

OBJECTIVE QUESTIONS

1. Hydrogenation of butene yields 

a. Butyne 

b. butane

c. pentene

d. butanol

2. Geometric (cis- trans) isomerism is exhibited by

a. C₂H₂Cl₂

b. C₂H₆Cl

c. C₄H₁₀

d. C₅H₁₂

3. which of the following is the general formula for the alkenes

a. CnH2n-2

b. CnH2n

c. CnH2n+2

d. CnH2n+1

4. Alkenes underg the reactions

THEORY QUESTIONS

1. Use the reaction scheme below to answer the following questions 

(i).