Developing Fuels

Question 1

What is a π bond?

Answer 1

π bond is the sideways overlap of adjacent p orbitals above and below bonding atoms, there is restricted rotation (C=C bond)

Question 2

What is a sigma bond?

Answer 2

The overlap of s orbitals between the two atoms, there is free rotation around the single sigma bond (C-C bond)

Question 3

State the conditions for standard conditions

Answer 3

298K, 1M, 1 atm

Question 4

Define Enthalpy change

Answer 4

The heat energy change under constant pressure

Question 5

Why are alkenes more reactive than alkanes?

Answer 5

π bonds have lower bond enthalpy than sigma bonds, so require less energy to break them and react with another species.
C=C double bond is an area of high electron density, making it susceptible to attack by electrophiles.

Question 6

Will the ∆H of an exothermic reaction be + or - ?

Answer 6

Exothermic ∆H= -

Endothermic ∆H= +

Question 7

How does mean bond enthalpy relate to the strength and length of a bond?

Answer 7

Lower bond enthalpy means a weaker and longer bond.

Question 8

Define enthalpy change of reaction.

Answer 8

The enthalpy change when quantities of substances in standard states react completely under standard conditions.

Question 9

Define enthalpy change of formation.

Answer 9

The enthalpy change when 1 mol of a substance is produced from its constituent elements under standard conditions.

Question 10

Define enthalpy change of combustion.

Answer 10

The enthalpy change when 1 mol of a substance is burned completely in oxygen under standard conditions.

Question 11

Define enthalpy change of neutralization.

Answer 11

The enthalpy change when solutions of acid and alkali react together under standard conditions to produce 1 mol of water.

Question 12

Equation linking energy change, specific heat capacity…

Answer 12

q = mc∆T
Energy change (q) = mass x specific heat capacity x temp. change

Question 13

Define specific heat capacity

Answer 13

The energy required to raise 1kg of a substance by 1K without change of state.

Question 14

State Hess’ Law

Answer 14

The total enthalpy change of a reaction is conserved regardless of the route taken.

Question 15

What is the role of catalysts?

Answer 15

Catalysts speed up the rate of reaction by lowering the activation energy by providing an alternate reaction pathway

Question 16

What are heterogeneous catalysts?

Answer 16

Catalysts in a different state or phase than the species in the reaction

Question 17

How does a heterogeneous catalyst work?

Answer 17

A solid heterogeneous catalyst adsorbs molecules onto the active site on the surface, increasing proximity and weakening covalent bonds in the molecules, allowing the reaction to occur more easily and faster.

Question 18

What is catalyst poisoning?

Answer 18

When impurities in the reaction mixture bind to the catalyst’s surface, blocking the adsorption of molecules, reducing the activity of the catalyst.

Question 19

What is cracking?

Answer 19

The process of converting long chain hydrocarbons into shorter, useful hydrocarbons by breaking carbon-carbon bonds (often producing alkenes as well).

Question 20

Explain the two processes of cracking.

Answer 20

Thermal cracking uses high pressure and temp., catalytic cracking produces aromatic compounds as hydrocarbon vapor is passed over a heated catalyst often at lower temp. (720K) and regular pressure.

Question 21

Why are hydrocarbons (alkanes) good fuels?

Answer 21

They release a lot of energy and, with sufficient oxygen, fully combust.

Question 22

Explain what incomplete combustion is. What are the products?

Answer 22

If oxygen is insufficient, incomplete combustion occurs. Products vary, can include C, CO, CO2, + H2O depending on oxygen levels.

Question 23

Explain why CO is dangerous.

Answer 23

It is a toxic, odorless gas which replaces oxygen in red blood cells, starving brain & organs with oxygen, leading to suffocation.

Question 24

What are the other byproducts of alkane combustion, and how are they harmful?

Answer 24

Nitrogen and sulfur oxides react with water in clouds to produce acid rain, damaging buildings, lakes and wildlife.
Carbon particulates of unburnt fuel can cause respiratory problems and global dimming.

Question 25

What is a catalytic converter and what is it used for?

Answer 25

This involves a rhodium catalyst to convert harmful particulates (CO, NOx, etc.) into stable products such as H2O and CO2.

Question 26

Define a hydrocarbon.

Answer 26

Compounds containing only carbon and hydrogen atoms.

Question 27

Define functional group.

Answer 27

A specific group of atoms or bonds within a compound that is responsible for the characteristic chemical reactions of that compound (i.e. alcohol -OH)

Question 28

Define homologous series.

Answer 28

A family of hydrocarbons with similar chemical properties who share the same general formula (i.e. CnH2n - alkene). (Increase in boiling point as chain length increases).

Question 29

What is the difference between aliphatic and aromatic compounds?

Answer 29

Aliphatic compounds are straight or branched carbon chains.

Aromatic compounds contain benzene rings.

Question 30

Explain the naming system for alkanes.

Answer 30

Stem - longest carbon chain prefixes: 1(meth-), 2(eth-), 3(prop-), 4(but-), 5(pent-), etc.
Functional group suffix: alkane (-ane), alkene (-ene), alcohol (-ol), cycloalkane(cyclo-)
Halogen prefix: F(Fluoro-), Cl(Chloro-), Br(Bromo-), I(Iodo-)
Side chain alkyl groups C chain number: 1(methyl), 2(ethyl), etc.
Side chain number given from closest to first C
More than one side chain/functional group prefix: 2(di-), 3(tri-), 4(tetra-), etc.
E.g. 2,2-dimethylpropane

Question 31

Describe the structure of a benzene ring.

Answer 31

Benzene (C6H6) is a ring of 6C each bonded to one H, with a ring of delocalized electrons

Question 32

What is a saturated and unsaturated compound?

Answer 32

Saturated: Contain C-C single bonds only
Unsaturated: Contain C=C double bonds, triple C bonds, or an aromatic ring.

Question 33

What is an alkene?

Answer 33

An unsaturated hydrocarbon with at least one C=C double bond, part of a homologous series of CnH2n.

Question 34

Explain the naming system for alkenes.

Answer 34

Identify longest C chain with C=C bond, counting closest to C=C bond, following prefix rule like alkanes
Suffix of 1-ene, 2-ene, etc. wherever double bond is.
Side chains prefix like alkanes
E.g. 4-methylhex-1-ene

Question 35

What is the order of priority of alkene naming suffixes?

Answer 35

(Highest to lowest): Carboxylic acid (-anoic acid), aldehyde (-al), ketones (-one), alcohol (-ol), alkene (-ene), haloalkane (-ane)

Question 36

What is an electrophile? Give examples of common electrophiles.

Answer 36

An electron acceptor that is attracted to areas of high electron density.
E.g. HBr, Br2, H2SO4

Question 37

Describe a test for the presence of alkenes.

Answer 37

Bromine water changes color from orange-brown to colorless when an alkene is present, as the C=C bonds ‘open up’ to accept Br atoms, becoming a saturated dibromo compound.

Question 38

What is an electrophilic addition reaction?

Answer 38

The reaction mechanism showing how electrophiles ‘attack’ alkene C=C double bonds

Question 39

Describe the electrophilic addition reaction of alkene with Br2.

Answer 39

As Br2 approaches alkene, π bond electrons repel electron pair in Br-Br bond, inducing a dipole, Br2 becomes polar and electrophilic. The intermediate has formed, with a C+ carbocation. Br bonds with carbon, forming dibromoalkane.

Question 40

What is Markownikoff’s Rule?

Answer 40

Bromine will be added to carbon with fewest Hydrogens attached to it. Because

Question 41

What are the 4 main types of electrophilic addition reactions?

Answer 41

1) Hydrogenation: using a nickel catalyst, producing an alkane
2) Halogenation: producing a monohaloalkane
3) Halogenation: producing a dihaloalkane
4) Hydration: producing an alcohol under high temp. (300-600ºC) and high pressure (70atm) with concentrated phosphoric acid (H3PO4) catalyst.

Question 42

What is a stereoisomer?

Answer 42

A compound with the same structural formula but a different spatial arrangement of atoms and bonds.

Question 43

What is an E and Z isomer?

Answer 43

E isomer is when H atoms are on alternating sides.

Z isomer is when H atoms are on the same side.

Question 44

What is a nucleophile?

Answer 44

An electron pair donor, it is electron rich so attracts electrophiles.

Question 45

Explain how E/Z isomerism arises.

Answer 45

Due to limited rotation of π bond in C=C double bond, so H atoms are either on alternating or the same sides.

Question 46

Explain how E/Z isomerism affects physical properties of compounds.

Answer 46

Z isomers have H atoms on the same side, which have a partial + charge, creating a polar compound.
E isomers have alternating side H atoms, creating a non-polar compound.

Question 47

State the ideal gas equation

Answer 47

pV = nRT
p = Pressure in Pa
V = volume in m3
T = temperature in K
n = moles
R = gas constant = 8.314 J/K/mol