F322 Chemistry

Define empirical formula

The simplest whole number ratio of atoms of each element present in a compound

Define molecular formula

the actual numbr of atoms of each element in a molecule

Define general fomula

The simplest algebraic formula of a member of a homologous series, i.e. for an alkane CnH2n+2

Define Structural Formula

The minimal detail that shows the arrangement of atoms in a molecule e.g. for butane : CH3CH2CH2CH3

Define displayed formula

The relative positionin gof atoms and the bonds between them.

H H

H---C---C---O-H

H H

Define skeletal formula

the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups

What is a homologous series?

A series of organic compounds having the same functional group but with each successive member differing by CH2

What is a functional group?

It is a group of atoms responsible for the characteristic reactions of a compound

What are the names of the first ten members of the alkanes homologous series

Methane

Ethane

Propane

Butane

Pentane

Hexane

Septane

Octane

Nonane and Decane

What is a structural isomer?

compounds with the same molecular formula but different structural formulae

What is a stereoisomer?

compounds with the same structural formula but with a different arrangement in space

What is E/Z isomerism?

It is an example of steroisomerism. When an organic molecule has a carbon-carbon double bond, the bonds are unable to rotate about the double bond. two dfferent groups must be attached to each carbon atom of the C=C for this kind of isomerism to occur.

What is cis/trans isomerism?

It is a special case of E/Z isomerism in which two of the substituent groups are the same. They will either be both above the C=C bond or one above and one below.

Describe the different types of covalent bond fission

There is homolytic bond fission which forms two free radicals when the bond breaks, and an electron goes to each atom

There is heterolytic bond fission which forms a cation and an anion. When the bond breaks, both electrons in the covalent bond go to one atom.

Describe giving an example and equations, the reaction mechanisms of free radical substitution

Initiation : chlorine molecule splits by homolytic fission in the presence of UV light

CL2 --> Cl . + Cl .

Propagation: Free radicals react with other molecules to always produce a free radical

Cl . + CH4 --> CH3 . + HCL

CH3 + CL2 --> CH3CL + CL .

Termination: two free radicals react to end the reaction

CL. + CL. --> CL2

CH3. + CL. --> CH3CL

How do you calculate atom economy?

Molecular mass of the desired products / sum of molecular masses of all products x 100

What atom economy do addition reactions have?

100% atom economy

what type of reaction is less atomically economical than addition reactions?

Substitution reactions

What are the benefits of developing chemical processes with a high atom economy?

You get more for your money and it reduces waste to the environment

What is a hydrocarbon?

A compound that contains only hydrogen and carbon

How is crude oil separated?

Different fractions of hydrocarbons in crude oil have different boiling points so condense at different temperatures in the fractional distillation column.

What kind of hydrocarbons are saturated hydrocarbons

Cycloalkanes and alkanes ( no double bonds)

what kind of shape is formed around each carbon atom in a hydrocarbon?

a tetrahedral shape

Describe and explain the trend in boiling points between long chain alkanes and short chain alkanes

Long chain alkanes have a higher boiling point as there are more Van der Waals forces in the molecule so requires more energy to overcome

Describe and explain the trend in boiling points between branched and straight chain alkanes

Branched chain alkanes have a lower boiling point than straight chain alkanes as there are less contact points for Van der Waals forces so less Van der Waals forces to overcome.

What is produced from the combustion of alkanes?

Water and CO2

What is produced from the incomplete combustion of alkanes. Give an equation

Carbon monoxide and water

CH4 + 2.5O2 --> CO + 2H2O

What is catalytic cracking?

The break down of long chain alkanes to short chain alkanes and alkenes by thermal decomposition using heat and a zeolite catalyst at 450 degrees C

Why does cracking make more useful fuels?

Because short chain alkanes have a lower boiling point than long chain alkanes so combust more efficiently. Alkenes are used in the plastics industry

why are straight chain hydrocarbons changed into branched alkanes and cyclic hydrocarbons?

Branched chain alkanes and cyclic alkanes are used as additives in fuels to promote efficient combustion

How are straight chain alkanes changed into cyclic hydrocarbons and arenes and what else is produced?

Reforming using an ALO3 catalyst and 150 degrees C. Hydrogen is produced which is used in the manufacture of ammonia and margerine

What the problems associated with fossil fuel use?

We develop an over-reliance on non-renewable fossil fuel reserves that will one day run out. We need to spend more money on developing renewable plant based fuels I.e biodiesel. Increased CO2 levels from combustion of fossil fuels is leading to global warming and climate change.

What is a free radical?

A species with an unpaired electron

What hydrocarbons are unsaturated hydrocarbons?

Alkenes and cycloalkenes

How is a pie bond formed?

by the overlapping of p orbitals on adjacent carbon atoms with a C=C double bond

State and explain the shape around each Carbon atom in a C=C double bond

trigonal planar - 3 areas of electron density - 2 pie bonds and a sigma bond

How do alkenes react to form alkanes?

They react with hydrogen in the presence of a nickel catalyst and 150 degrees C in an addition reaction

How do alkenes react to form dihalogenoalkanes?

They react with halogens e.g. reacting with bromine to detect a C=C double bond and thus the unsaturation of a molecule.

How do alkenes react to form halogenoalkanes?

They react with a hydrogen halide

How do alkenes react to form alcohols?

They react with water, H3PO4 catalyst, heat and pressure to form an alcohol

What is an electrophile?

An electron pair acceptor

Describe an electrophilic addition reaction

There are 2 ( bromine and hydrogenbromide)

HBr

The HBr has a permanent dipole as Br is more electronegative than hydrogen. The delta +ve hydrogen attracts the electrons in the Pie bond of the alkene. The HBr bond splits by heterolytic fission forming a carbocation and Br- ion. Then Br- ion with a lone pair and carbocation react to form a halogenoalkane.

With bromine, the electrons in the pie bond of the alkene repel the electrons in the Br2 bond, inducing a dipole. Then the same thing happens as before.

What kind of reaction takes place when alkenes polymerise?

addition polymerisation - the C=C bond opens up

What is the repeat unit of polypropene?

CH3 H

------------C----------C-------------

H H

How are alkenes used in the manufacture of margarine ?

Alkenes react with H2 gas and a nickle catalyst to produce an alkane and hydrogen which is used to saturate vegetable oils in hydrogenation

What are the different types of polymer disposal?

Separation of plastics into types and recycling

- sometimes done by hand, sometimes done by scanning. Types must be labelled

Combustion for energy production

- Burnt to produce heat energy

- Not alot is produced so household waste is added which releases toxic gases

-PVC release HCL so needs alkaline scrubbers to remove gases

Feedstock for cracking

- crack waste into smaller molecules then use as a feedstock to produce plastics

What are chemists trying to do to minimise harm to the environment with polymer disposal?

They are trying to remove toxic waste products eg HCL

They are developing biodegradable and compostable polymers i.e. isoprene maize and starch

Explain the water solubility and relatively low volatility of alcohols

They hydrogen bonding that occurs with alcohols gives them a very high boiling point and low volatility. Solubility decreases as the chain length increases as a larger part of the alcohol is made up of a non-polar HC chain. The HC chain does not form H bonds with water.

How is ethanol produced?

The fermentation of sugar

C6H12O6 ---------------> 2CH3CH2OH + 2CO2

using yeast, no oxygen and 37 degrees C

This is used by the drinks industry and in biofuels

Reacting ethene with steam and H3PO4 catalyst

CH2=CH2 + H2O -----> CH3CH2OH

How are alcohols used?

Alcoholic drinks

Sterilizing

Solvents

Biofuels

Fuel dditives

Chemical Feedstocks

How do you classify alcohols?

Primary - The -OH group is attached to a C atom with no, or one alkyl group

Secondary - The -OH group is attached to a C atom bonded to two alkyl groups

Tertiary - The -OH group is attached to a C atom bonded to three alkyl groups

What do alcohols combust to form?

CO2 and H2O

What is the oxidising agent that is used for the oxidation of alcohols?

Acidified potassium dichromate

What is the colour change in the dichromate?

Orange ---> green

What kind of alcohol is oxidised to produce an aldehyde, carboxylic acid and ketone?

Primary is oxidised to form an aldehyde and then refluxed to form a carboxylic acid

Secondary is oxidised to form a ketone

Tertiary doesn't oxidise

What is reflux?

the continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry

How is an ester produced?

Alcohol + Carboxylic acid ------> Ester + Water

It uses concentrated Sulfuric acid.

An ester is formed from the removal of a water molecule ( H from the alcohol and OH from the carboxylic acid)

How is an alkene formed from an alcohol?

Dehydrating the alcohol using concentrated sulfuric acid and heat

C4H10O ---------> C4H8 + H2O

The removal of water molecules from adjacent C atoms. This is an elimination reaction

What kind of reaction is the hydrolysis of halogenoalkanes?

nucleophilic substitution

Describe a nucleophilic substitution reaction

The C--X bond is polar and the hot aqueous NaOH disassociates to form a Na+ ion and OH- ion. The OH- is attracted to the delta positive C atom. The electrons in the C---X bond are repelled by the OH- ion so the bond breaks and forms a C---OH bond and an X- ion and Na + ion.

What is a nucleophile?

An electron pair donor

Explain the rates of hydrolysis of primary halogenoalkanes in terms of relative bond enthalpies of carbon - halogen bonds

Down the halogen group, bond enthalpies are less so the C-X bond is weaker making it more reactive as the bond is more easily broken.

What is chloroethene and tetrafluoroethene used for?

PVC and PTFE ( teflon)

Why are halogenoalkanes good aerosols?

They have a low boiling point so evaporate at room temperature. They have a low reactivity, volatility and are non toxic

How do CFCs cause environmental damage?

CFC's don't break down in the lower atmosphere. They are broken down in the stratosphere by UV light to produce free radicals CL . which catalyse the breakdown of O3.

What is the role of green chemistry in minimising damage to the environment with regard to CFCs

They promote biodegradable alternatives to CFCs such a hydrocarbons and HCFCs, they use CO2 as a blowing agent. They banned the use of CFCs

What happens to covalent bonds when they absorb infra-red radiation?

The bonds vibrate

How do breathalysers work?

They measure ethanol in the breath by analysis using infra-red spectroscopy

How can you use Mass Spectrometry to determine the relative isotopic mass or a substance?

The Mr of the M+ ion is the last peak on the chart

How is Mass Spectrometry used as a method for identifying elements?

It is used in the Mars space probe and in monitoring levels of environmental pollution, such as lead.

What is a mass spectrum essentially?

It is a fingerprint of the molecule that can be identified by a computer using a spectral database

What is the enthalpy change for an exothermic and endothermic reaction?

exothermic - A negative enthalpy change

endothermic - A positive enthalpy change

What kind of typical reactions are exothermic and endothermic reactions?

exothermic - oxidation such as the combustion of fuels and the oxidation of carbohydrates such as glucose in respiration. Making brine. All neutralisation reactions

endothermic - Thermal decompositions ( limestone) Photosynthesis and cracking. All of these require the input of heat to start the reaction

Draw the 2 enthalpy profile diagrams of endothermic and exothermic reactions

Define activation energy

Activation energy is the energy needed to start a reaction. It provides energy to break bonds.

What are standard conditions and why do we need them?

Temp 25 degrees c

pressure 1 atmsophere

conc. 1.0 mol/dm3

You can only compare reactions if they conditions are the same

Define enthalpy change of reaction

It is the enthalpy change when the molar quantities of reactants shown in the equation for the reaction, react under standard conditions to give the products of their standard states

Define the enthalpy change of formation

It is the enthalpy change when one mole of compound in its standard state, is made from its elements in their standard states under standard conditions

Define enthalpy change of combustion

It is the enthalpy change when one mole of a substance burns completely in oxygen gas to form products in their standard states under standard conditions

What is the equation to calculate energy change?

Q = m x c x delta T

m is the mass of the solvent

c is the specific heat capacity

delta T is the change in temperature

What makes a reaction endothermic or exothermic?

A reaction is endothermic when the energy released from forming new bonds is less than the energy required to break the existing bonds.

A reaction is exothermic when the energy released from forming new bonds is more than the energy required to break the existing bonds.

Define average bond enthalpy

The energy required to break one mole of a particular type of bond in gaseous molecules under standard conditions. The average of X--Y bond enthalpies measured in different compounds.

Define Hess's law

The total enthalpy change for a reaction is the same for any reaction route, provided that the starting and finishing conditions are the same

What is the effect of concentration on the rate of reaction?

Increasing the concentration increases the rate of reaction because there are more particles in the same volume therefore collisions are more probable and so more frequent. It has no effect on probability of success.

What is the affect of an increase in pressure of a gas on the rate of reaction?

The higher the pressure, the faster the rate of reaction as the same number of particles are now in a smaller volume so collisions are more probable and so more frequent. It has no effect on the probability of success

How is a catalyst useful in a reaction?

It speeds up a reaction without being consumed by the overall reaction

Explain how catalysts work

Catalysts affect the conditions that are needed, often requiring lower temperatures and reducing energy demand and CO2 emissions from burning of fossil fuels.

They enable different reactions to be used with better atom economy and with reduced waste

They are often enzymes, generating very specific products and operating effectively close to room temperatures and pressures

Some have great economic importance e.g. iron in ammonia productions.

Explain using enthalpy profile diagrams, how a catalyst speeds up a reaction

A catalyst allows a reaction to proceed via a different route with a lower activation energy, giving rise to an increased reaction rate.

Explain the Boltzmann distribution and its relationship with activation energy

The graph describes the distribution of energy between the particles in a liquid or gas system. The average energy corresponds to T. The Area is the total number of particles in the system. The smaller area indicates the number of particles that have Ea.

Describe the effects of temperature on the Boltzmann distribution curve

The lower the temperature, the curve shifts to the left and is higher and less molecules have the activation energy. They higher the energy the curve shifts to the right and is lower and more particles have the Ea. The area under the curve must stay the same because the total number of particles in the system does not change.

When does a dynamic equilibrium exist?

When the rate of the forward reaction is equal to the rate of the reverse reaction

State le Chatelier's principle

Any change in the conditions of an equilibrium system will result in a shift of the equilibrium position in the direction that opposes that change.

Why is important for industry to compromise between chemical equilibrium and rate of reaction?

If the temperature needs to be low to have a high yield, the reaction will be too slow so a medium temperature is needed.

What are the limitations of radical substitution in synthesis?

products are difficult to predict as the reactions are hard to control as eg for methane and chlorine you could get CH2Cl2 as well as normal products when substitution proceeds further. Therefore atom economy is potentially low.

What kind of bonds is infra-red radiation absorbed by?

C=O, O-H and C-H bonds in H2O, Co2 and CH4

What two factors affect the greenhouse effect of a given gas?

The gas's atmospheric concentration and its ability to absorb infra-red radiation

Why must we control global warming?

Global Warming causes climate change, which threatens habitats and weather systems all over the world.

What are the ways in which chemists minimise climate change resulting from global warming?

They provide scientific evidence to governments to verify that global warming is taking place

They investigate solutions to environmental problems such as carbon capture and storage.

They monitor progress against initiatives such as the Kyoto protocol

What is carbon capture and storage?

Capturing CO2 and pumping it into air reserves deep under the sea that used to be used for oil drilling. It is then stored in these large cavities. Injection of CO2 into stable geological structures such as oil and gas fields, unminable coal beds and deep saline formations.

How is the ozone sustained?

Ozone is continuously being formed and broken down in the stratosphere by the action of ultraviolet radiation.

O2 + O --> O3

O2 + uv light ---> O

O3 + uv light ---> 2O2