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Chemistry Lesson

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Jessica Bunting

on 17 October 2010

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Transcript of Chemistry Lesson

Polyethylene What the?
ETHYLENE
POLYETHYLENE Addition Polymerisation 1. Initiation
2. Propagation
3. Termination Initiation Propagation + Propagation Polymerisation Start Mid End Lots of monomer

Mostly short polymer chains Some monomer remains

Mix of long and short polymer chains Little monomer remains

Many long polymer chains Types of Polyethylene Low density polyethylene

High temperature
High pressure Low temperature
Low pressure
Catalyst

High density polyethylene Do you know of any other common polymers? Can you name this common polymer? What about this one? Vinyl Chloride PVC is made from the monomer vinyl chloride Vinyl Chloride PVC is made from the monomer vinyl chloride Vinyl Chloride Can you provide the systematic name? Vinyl Chloride Chloroethene Poly(vinyl chloride) Can you provide the systematic name? Systematic name: poly (1-chloroethene) Poly(vinyl chloride) Styrene Polystyrene is made from the monomer styrene Styrene ? Benzene ring.
When is a side group called a phenyl group Shorthand Styrene What is the systematic name? Polystyrene The properties of polymers are affected by their structure Average molecular weight (chain length)
Chain branching
Chain stiffening
Cross-linking
Stability Structural Properties Average molecular weight (chain length):
The higher the molecular weight, the higher the melting point and the harder the substance is.
Chain branching Unbranched chains lead to high density, high melting point, and relatively hard and tough material.
Structural Properties Chain Stiffening
Large side groups reduce chain flexibility, causing the polymer to become stiffer and more rigid Stability
C-C and C-H bonds are very stable
C-Cl bonds break in the presence of UV light Structural Properties Cross linking
Cross linking increases rigidity and hardness. Not common in addition polymers PVC The Cl side group provides significant chain stiffening, causing PVC to be hard and inflexible PVC Plasticisers can be added to soften and increase flexibility PVC C-Cl cond is vulnerable to UV attack, therefore degrades fairly quickly in daylight. Needs an inhibitor for outdoor use. Polystyrene The large phenyl side group dramatically stiffens chain, hence is very hard and rigid.
Very stable. Polystyrene Minimal chain branching, hence is very dense and clear ? ALKANOLS ALKANOLS Alkanols are more commonly known as alcohols
They are distinguishable by their OH (hydroxyl) functional group attached to an alkane.
CH3CH2OH
How can they be made? One method to make an alcohol is by an addition reaction of ethene and water with a catalyst Combustion Alcohols burn in oxygen to produce carbon dioxide and water. Combustion Alcohols burn in oxygen to produce carbon dioxide and water. CH3CH2OH + 3O2 2CO2 + 3H2O

Molar heat of combustion The molar heat of combustion of a substance is the heat liberated when one mole of the substance undergoes complete combustion with oxygen at standard atmospheric pressure with the final products being carbon dioxide gas and liquid water. = how much energy is released by 1 mol of a substance (alcohol for today!) when it is combusted. Molar heat of combustion Ethanol Molar heat of combustion As heat is absorbed the temperature of the water increases Molar heat of combustion 1.) q = mC∆T 1.) q = mC∆T Molar heat of combustion What we are assuming is that:
heat released by combustion of ethanol = heat absorbed by water heat released by combustion of ethanol = heat absorbed by water Molar heat of combustion What we are assuming is that:
1.) q = mC∆T HOWEVER! What we are assuming is that:
heat released by combustion of ethanol = heat absorbed by water 1.) q = mC∆T Molar heat of combustion From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
We need to identify important information in the question From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
q= mC∆T
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
From the reaction below, 4.6g of ethanol was needed to raise the temperature of 0.2kg of water by 20 K-1. Using this information calculate the molar heat of combustion of ethanol
11:30 -12:30 First Year Chemistry Lab
41-340
Reacting alkanes and alkenes with bromine water
Heat combustion of alkanols PRAC!!!! WELCOME TO UOW! Lecture: Sarah, Aaron, Jeff and Jess Alkanes and alkenes
Production of Ethylene
Polymerisation
Properties and uses of PVC and polystyrene
Molar heat of combustion of alkanols. Practical: Reactions of alkanes and alkenes with bromine water
Molar heat combustion of alkanols: methanol, ethanol and propanol. Alkanes and Alkenes Alkanes are saturated hydrocarobons: they contain only carbon-carbon single bonds and the maximum number of hydrogen atoms per chain Alkenes are unsaturated hydrocarbons because they contain one carbon-carbon double bond ALKANES ALKENES ETHANE IUPAC name: ETHENE preferred historical name: ETHYLENE Alkenes have similar physical properties (boiling point, densitites and solubilities) to their corresponding alkanes. HOWEVER Alkenes are more chemically reactive WHY??? The presence of the DOUBLE BOND in alkenes makes them more reactive because they readily open their double bond to bond with other molecules. These are called addition reactions Testing for ALKENES Reaction with bromine water The very reactive double bond in ethylene means that it can be easily converted into a range of useful products such as ethanol and is the starting materials for several important plastics (polymers). Production of Ethylene CRACKING! The chemical process of breaking large hyrdrocarbon molecules into smaller ones. It ranks as one of the top five products produced by the chemical industry worldwide! Crude oil is a natural mixture of hydrocarbons Catalytic Cracking Thermal Cracking A mixture of alkanes with steam is passsed through very hot metal tubes. The alkanes decompose completely into small molecules such as ethylene. Provides the best yield of ethylene. Involves the use of a catalyst (zeolite: an aluminium silicate) and therefore occurs at lower temperatures. The end result are alkanes of shorter chain lengths (used for fuel) and small alkenes such as ethylene. Production of ethylene using catalytic cracking alone is insufficient to meet current demands Termination Styrene phenylethene Why are we interested? Alkanols are so great because they readily burn!!
i.e. they are combustible
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