LC CHEMISTRY- TYPES OF CHEMICAL REACTIONS

REBECCA'S CHEMISTRY- TYPES OF CHEMICAL REACTIONS KNOWT

substitution reaction

chemical reaction in which an atom or group in a molecule is replaced by another atom or group of atoms

substitution reaction example

mechanism of reaction

step by step description of how a overall reaction occurs

nitrogen and hydrogen toform ammonia

purpose curly arrows

show electron movement

movement of one electron

movement of pair of electrons

1. initiation

convert the chlorine molecule into two chlorine free radicals

a photochemical reaction

it takes place rapidly if the mixture is exposed to ultraviolet light. The fact that UV light causes the reaction is evidence for the mechanism since UV light possesses enough energy to break the Cl–Cl bond. This step is often called the initiation or starting stage of the reactio

3. propagtion

one of the Cl radicals attacks the m

4. termination

When most of the reactants have been used up during Steps 2 and 3, there are only a small number of Cl radicals and methyl radicals left over. These combine to form Cl2, chloromethane and ethane.

what mechanism example identical to the innerworkings of this reaction

the monochlorination of ethane is identical

evidence 1: reaction takes place when exposed to UV light

example 1: suggests a free-radical mechanism whereby Cl2 is broken down into Cl radicals

evidence 2: for every photon of UV light used, thousands of chloromethane molecules are formed

explaination 2: suggests a chain reaction is involved

evidence 3: addition of an inhibitor, like O2, slows down the reaction

explanation 3: shows a chain reaction is taking place, as O2 combines with free radicals, stopping the chain reaction.

esterfication

when carboxylic acid reacted with alcohol with a small amount of H₂SO₄ as a catalyst, an ester formed. A substitution reaction because H on COOH is relaced by the a aklyl like methyl or ethyl

esterfication

acid hydrolysis creates a reversible reaction carboxylic acid and alcohol

base hydrolysis creates a irreversible reaction carboxylate salt and alcohol, saponification how soap is made

hydrolysis

larger molecule is broken down into smaller parts by adding water

saponification

hydrolisis of esters with a base is added like NaOH or KOH it results in formation of the sodium and potassium salt of the carboxylic acid, this is unreversiblke reaction due to teh base

addition reaction

one in which two or more molecules react together to form a single molecule

addition reacton properties

1. Will always occur on a double/triple bond.

2. Geometry will change from planar (unsaturated C-C bonds) to tetrahedral (saturated C-C bonds).

3. Benzene does not undergo addition reactions as its delocalised electrons make it very stable and unreactive.

uses for addn reactions

1. chloroethane formed by the reaction between ethene and hydrogen chloride is used in dentistry as means of diagnosing a dead tooth. A small amount of the substance is placed on the tooth and because of the low boiling point of the liquid, this creates a localised chilling effect, if tooth alive, the chilling felt by patient

2. 1,2- dichloromethane formed by the reaction between ethene and bromine is used to manufacture chloroethane, used to make polyvinyl chloride (PVC), a widely used plastic

ethene + hydrogen bond =

ethane

ethene + chlorine bond =

1,2-dichloroethane

ethene + hydrogen chloride bond=

chloroethane

ethene + water

ethanol

ethene + bromine bond=

1,2- dibromoethane

difference between animal and vegetable fat

animal usually saturated and unsaturated vegetable fats

bromination of ethene is an example of

ionic addition reaction

mechanism

a detailed step-by-step description of how the reaction occurs

name the steps of Bromination of ethene

1. polarisation

2. heterolytic fission

3. carbonium ion formation

4. ionic attack

Polarisation (bromination of ethene) EXPLAIN AND DRAW

• c=c double bond in ethane has a high concentration of negative charge

• As the Br₂ approaches the ethene, the electrons are repelled away from the ethene, polarisation the b₂

discuss for my own understanding deeper explanation of polarisation

the c=c double bond has high concentration due to the double bond of both sigma and pi bonds, the pi bonds holds more electrons because it’s a sideways overlap so extra electrons, whereas the sigma bond is regular regular head on basic overlap

where as for

Heterolytic fission (bromation of ethene) EX

the polarisation eventually becomes so great, the molecule splits into Br- and Br+ . we call this heterolytic fission because the Br-took all 2 electrons from the Br-Br bond. (Br- IS BEING GREED ITS HETERO 1 ELEMENT TAKING 2 ELECTRONS)

carbonium ion formation (bromination of ethene) EXPLAIN AND DRAW

The Br+ attacks the electron rich C=C double bond. This forms a carbonium ion (positive charge on C)

UNDERSTANDING carbonium ion formation deeper

c=c double bond IS BROKEN to form sigma bond with bromine, this leaves only a single sigma bond between the two carbon atoms

ionic attack (bromination of ethene)

The Br⁺ on attacks the carbonium ion, forming 1,2-dibromoethane

WHAT TO DO TO WRITE TEH ADDITION OF CL₂ OR HCL

SIMPLY REPLACE THE BR₂

Evidence of the bromination of the ionic addition mechanism

If this reaction is carried out in bromine water with some Cl⁻ ions added, we see the normal 1,2-dibromoethane product being formed, but two other products form also; 1-bromo-2-chloroethane and 2-bromoethanol. These form because of the Cl⁻ or the OH⁻ (from water’s self-ionisation) can replace the Br⁺ in step 4.

polymerisation reaction is a type of

addition reaction

polymer definition

long chain molecules made by joining many small molecules (monomers, they are made of many repeating units e.g polyethene (made up of many ethene monomers)

Elimination reaction definition

one in which a small molecule is removed from a larger molecule, leaving a double bond on the larger molecule.

properties of an elimination reaction

1. geometry changes from tetrahedral to planar as a double bond is formed

2. generally involved the removal of a water molecule (H2O) – these are also called dehydration reactions

what is exclusive to dehydration elimination reactions

Al2O3 and heat is used to remove water

what occurs in the production of ethene

water is removed from the ethanol.
Al2O3 and heat is used to remove water from ethanol