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Chemistry > Alkenes and polymers > Flashcards

Alkenes and polymers Flashcards

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1
Q

What do alkenes contain?

A

A double carbon-carbon bond

Alkenes are characterized by the presence of a C=C bond.

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2
Q

What is the general formula for alkenes?

A

CnH2n

This formula indicates that alkenes have two fewer hydrogens than alkanes with the same number of carbons.

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3
Q

Why are alkenes considered unsaturated?

A

They have a double carbon bond

This results in two fewer hydrogen atoms than their alkane counterparts.

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4
Q

List the first four alkenes by the number of carbon atoms.

A
  • Ethene - 2 carbons
  • Propene - 3 carbons
  • Butene - 4 carbons
  • Pentene - 5 carbons

These are the simplest members of the alkene family.

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5
Q

What is the functional group of alkenes?

A

C=C

This represents the double bond characteristic of alkenes.

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6
Q

Are alkenes more or less reactive than alkanes?

A

More reactive

The presence of the double bond increases their reactivity.

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7
Q

What test can be performed to identify alkenes?

A

React with bromine water

A positive test results in the bromine water changing from orange to colourless.

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8
Q

What happens when alkenes burn?

A

They burn with a smoky flame

This is due to incomplete combustion, producing carbon and carbon monoxide along with water.

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9
Q

What occurs to the C=C double bond during reactions with alkenes?

A

It becomes a C-C single bond

This allows other atoms to join the carbon atoms that now have a free bond.

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10
Q

What does hydrogen react with in alkenes to form?

A

The equivalent saturated alkane

This reaction converts the double bond to a single bond.

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11
Q

What do water/steam react with alkenes to form?

A

Alcohols

This reaction is part of the hydration process of alkenes.

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12
Q

What do halogens react with alkenes to form?

A

A saturated molecule - the double bond breaks.

Each halogen bonds to a carbon atom in the alkene.

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13
Q

What is addition polymerization?

A

A process where many small molecules join to form very large molecules

The repeating unit in addition polymers has the same atoms as the monomer.

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14
Q

What type of bonds link atoms in polymer molecules?

A

Strong covalent bonds

This contributes to the stability of polymers.

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15
Q

What are the properties of polymers at room temperature?

A

They are solids

This is due to the relatively strong intermolecular forces between polymer molecules as they are very large molecules.

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16
Q

What is Low Density Poly(ethene) abbreviated as?

A

LDPE

This form of polyethylene has a branched structure.

17
Q

What is High Density Poly(ethene) abbreviated as?

A

HDPE

HDPE has a more linear structure compared to LDPE.

18
Q

What are the conditions to make LDPE?

A

Slightly raised temperature, high pressure, trace of oxygen

LDPE stands for Low-Density Polyethylene.

19
Q

What is the structure of LDPE?

A

Polymer chains have lots of branching

This branching affects the packing of molecules.

20
Q

What are the properties of LDPE?

A

Lower melting point, lower density, weaker substance

LDPE’s properties result from its branched structure which stop it from being packed as closely together so that the intermolecular forces are weaker.

21
Q

What are the conditions to make HDPE?

A

Slightly raised temperature, much lower pressure, catalyst

HDPE stands for High-Density Polyethylene.

22
Q

What is the structure of HDPE?

A

Polymer chains have little branching

The lack of branching allows for tighter packing of molecules.

23
Q

What are the properties of HDPE?

A

Higher melting point, higher density, stronger substance

HDPE’s properties are due to its linear structure which means it can be packed closely together and have stronger intermolecular forces.

24
Q

What effect does heating have on thermosoftening plastics?

A

Softens and melts easily so can be reset and remoulded

Thermosoftening plastics can be reshaped upon heating.

25
Q

What effect does heating have on thermosetting plastics?

A

Chars when heated and so the shape can’t be changed

Thermosetting plastics maintain their shape after initial setting.

26
Q

What is the structure of thermosoftening plastics?

A

Tangled web of chains which are easy to separate

This structure allows for flexibility and remoulding.

27
Q

What is the structure of thermosetting plastics?

A

Covalent bonds between chains called cross links which are hard to break and separate

The cross-linking provides strength and stability to thermosetting plastics.

28
Q

What does this show?

Add n bottom right of addition polymer.
A

Additional polymerisation.

Chemistry (16 decks)

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