Topic 10- Alkanes Flashcards Preview

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Flashcards in Topic 10- Alkanes Deck (9)
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1

What is the general formula for alkanes?

What is the general formula for alcohols?

What are alkanes a member of?

What are alkanes referred to and why (in full detail)?

How are the bonds spaced in alkanes?

What is the first examples of structural isomerism in alkanes?

What is the boiling point like as alkanes increase in size?

What does more atoms result in?

What does greater intermolecular force require?

What does greater energy required result in?

Cn H2n +2

Cn H2n +2 O

A homologous series

Saturated hydrocarbons- all carbon-carbon bonding is single

The bonds are spaced tetrahedrally about carbon atoms

First example of structural isomerism occurs with C4H10 (butane)

Boiling point increases as they get more carbon atoms in their formula

More atoms= greater intermolecular Van der Waals' forces

More energy to separate the molecules

Higher boiling point.

2

Why does the difference in boiling point get less as the size of alkanes increases?

What must be written in an exam about Van der Waals forces?

What do straighter chain molecules have that's better than branched?

What does the greater the branching result in?

What happens to melting point in alkanes?

What is this trend not as regular for?

What are alkanes, concerning polarisation?

What are they soluble in most?

Mass increases by a smaller percentage

Must write Van der Waals forces between molecules

Straighter chain molecules have greater interaction than branched

The greater the branching, the lower the boiling point

Melting point generally increases with molecular mass

Not as regular as that for boiling points

Non-polar so are immiscible with water (ie don't dissolve in water)

Alkanes are soluble in most organic solvents.

3

What is the reactivity of alkanes like?

What are the bonds like of alkanes?

What don't alkanes have on their structures?

What do alkanes make as useful reactants?

How do alkanes react with oxygen?

What does the greater the number of carbon atoms result in?

But does this then also require?

What is a handy tip for when balancing equations involving complete combustion (in full)?

Fairly unreactive

Have relatively strong, almost non-polar, single covalent bonds

They have no real sites that will encourage substances to attack them

Make useful fuels- especially lower members of the series

React with oxygen in an exothermic reaction

More energy produced

The greater the amount of oxygen needed for complete combustion

Every carbon in the original hydrocarbon gives one carbon dioxide and every two hydrogen atoms gives a water molecule.

4

Why does fractional distillation work?

What does longer chain hydrocarbons have?

What does industrial cracking involve?

What does industrial cracking convert?

What does thermal cracking proceed via?

What does catalytic cracking proceed via?

What is the pressure and temperature like of thermal cracking?

What are the two other properties of thermal cracking?

What does thermal cracking mostly produce?

What else does thermal cracking produce and what two processes is this then used in?

By what two processes can bonds be broken anywhere in the molecule?

Because the different substances in the mixture have different boiling points

Longer chain hydrocarbons have higher boiling points

The breaking of C-C bonds in alkanes

Long chain molecules into higher value products

A free radical mechanism

A carboncation (carbonium ion) mechanism

High pressure: 7000 KPa ; high temperature: 400 oC to 900 oC

Free radical mechanism and homolytic fission

Produces mostly alkenes (eg ethene for making polymers and ethanol)

Produces hydrogen... used in the Haber Process and in margarine manufacture

C-C bond fission or C-H bond fission.

5

What is the pressure and temperature of catalytic cracking like?

What type of catalyst is used?

What are two other properties of catalytic cracking?

What three things does catalytic cracking produce?

What are the products of catalytic cracking used for?

What are zeolites?

Slight pressure ; high temperature: 450 oC

Zeolite catalyst

Carboncation (ionic) mechanism and heterolytic fission

Produces branched and cyclic alkanes, aromatic hydrocarbons

Motor fuels

Zeolites are crystalline aluminosilicates; clay like substances

6

Describe fully what happens to shorter chain alkanes in complete combustion?

What are these combustion reactions described as and why?

What do they have concerning enthalpy?

What happens the more carbons present in an alkane?

What is useful about these properties of alkanes for us?

What are fuels?

What do fuels also do?

What happens to alkanes in a limited supply of oxygen?

What does this reaction produce?

What is produced if there's even less oxygen present?

What can be used when balancing diatomic gases?

The shorter chain alkanes burn completely in a plentiful supply of oxygen to give carbon dioxide and water

Exothermic because they give out heat

They have a large negative enthalpy of combustion

The greater the heat output

Important to us as fuels

Substances that release heat energy when they undergo combustion

Fuels also store a large amount of energy for a small amount of weight

They burn in incomplete combustion

The poisonous gas carbon monoxide, CO

Carbon (soot) is produced

Half of a compound can be used.

7

Describe the following by products/products of the combustion of alkanes (in full detail):

Carbon Monoxide

Nitrogen Oxides

Sulphur Dioxides

Carbon Particles

Unburnt Hydrocarbons

Carbon Dioxide

Water Vapour


What two things do sulphur oxides combine with and what does this form?

What two things are nitrogen oxides contributors to?

CO, a poisonous gas produced by incomplete combustion

Abbreviation NOx, produced when there is enough energy for N2 and O2 in the air to combine

Another contributor to acid rain. Produced in sulphur-containing impurities present in crude oil

Called Particulates. Can exacerbate (make worse) asthma and cause cancer

May also enter the atmosphere and these are significant greenhouse gases. Contributes to photochemical smog which can cause a variety of health problems

A greenhouse gas. Always produced when hydrocarbons are burnt. Although CO2 is necessary, increasing rise in atmosphere which could be a contributing factor to climate change and global warming

Also a greenhouse gas

Combine with water vapour and oxygen in the air to form sulphuric acid

Acid rain and photochemical smog.

8

What do power stations cause concerning pollution?

What three things do internal combustion engines produce?

What does effluent mean?

How is SO2 removed?

How are CO and NOx removed?

What happens to the following in a catalytic converter:

CO

NOx

Unburnt Hydrocarbons

What three metals are catalysts made from?

What two things does leaded petrol do to catalytic converters if it passes through it?

SO2 emissions which produce acid rain

CO, NOx and unburnt hydrocarbons]

Waste (either liquid/gas)

React effluent gases with a suitable compound (eg CaO)

Pass exhaust gases through a catalytic converter

CO is converted to CO2

NOx is converted to N2

Unburnt hydrocarbons are converted to CO2 and H2O

Finely divided rare metals Rh, Pd and Pt

-Lead deposits on the catalysts surface and poisons it
-Thus blocking sites for reactions to take place.

9

Why is water not a problem as a greenhouse gas?

What are unburnt hydrocarbons and give an example?

What does carbon dioxide do in the Earth's atmosphere and what is the result?

What does visible radiation do to the atmosphere and what does this cause?

What is emitted by the Earth and what does this do?

What is some of this trapped by and why?

Because the amount in the atmosphere stays roughly constant

Potent greenhouse gases (methane from animals is a problem)

Carbon dioxide traps infra-red radiation so that the Earth's atmosphere heats up

Visible radiation (sunlight) readily penetrates the atmosphere and warms the Earth

Invisible infra-red radiation is emitted by the Earth and cools it down

Some of this infra-red radiation is trapped by greenhouse gases in the atmosphere, keeping the heat in.