[Year 1] DF Flashcards
What are stereoisomers?
Isomers with the same structural formula but a different arrangement of atoms in space.
Why does stereoisomerism occur in alkenes?
The C=C (pi bond) cannot rotate and is rigid.
Thus you get E/Z isomerism.
When do you get E isomers?
When the atoms that are the same are on opposite sides.
When do you get Z isomers?
When the atoms that are the same are on the same sides.
What is electrophilic addition?
When alkenes are attacked by electrophiles due to their double bonds high electron density.
How do you show an electrophilic addition reaction?
- Curly arrow.
- From double bond to positive.
What are the reaction conditions to react to hydrogen gas with ethene?
150⁰C and Nickle catalyst
OR
RT and Platinum catalyst
How can we test for alkenes?
Decoloration of bromine water.
- Add bromine water to alkene.
- Brown-orange to colourless.
Why does the test for alkenes work?
- Bromine is polarised when it gets near alkene as the electrons in the C=C bond repels electrons in Br₂
- This make Bromine an electrophile.
What happends in the intermediate when testing for alkenes?
A carbocation is formed
Br⁻ is formed.
Draw the mechanism for the test for alkenes.
Google search answer.
FIRST
- Arrow from C=C to δ+ Br
-Arrow from Br-Br to δ- Br
INTERMEDIATE
- Br bond with C
- No more double bonds
- Carbocation shown by C⁺
- Bromide ion show by Br⁻ with outer electrons shown.
LAST
- 1,2-dibromoalkane drawn.
What happend as a result of the hydration of alkenes?
Alcohos produced.
What the reaction conditions in the hydration of alkenes?
Water must be gas.
300⁰C and 60atm.
Phosphoric acid catalyst (H₃PO₄).
Show the reaction for the hydration of ethene?
ethene + water(g) ⇌ ethanol
Other than hydartion how can alcohols be made?
Alkyl hydrogen sulfates with sulfuric acid being re-formed.
How are alcohols made with alkyl hydrogen sulfates?
- Cold water added to warm ethyl hydrogen sulfate. (hydrolysis)
How does the making of alcohols with alkyl hydrogen sulfates show sufuric acid is a catalyst?
Sulfuric acid is reformed.
H₂C=CH₂ + H₂SO₄ → CH₃CH₂OSO₂OH
CH₃CH₂OSO₂OH + H₂O → CH₃CH₂OH + H₂SO₄
How are halogenoalkanes formed?
Alkene + Hydrgen Halides.
Give an example of the mechanism to form halogenoalkanes.
use HBr and ethene
Google search answer.
FIRST
- Arrow from C=C to δ+ H
-Arrow from H-Br to δ- Br
INTERMEDIATE
- H bond with C
- No more double bonds
- Carbocation shown by C⁺
- Bromide ion show by Br⁻ with outer electrons shown.
LAST
- bromoethane drawn.
What happends when hydrogen halides react with unsymmetrical alkenes?
2 products made
Give an example of the mechanism between hydrogen halides and unsymmetrical alkenes?
(use HBr and Prop-1-ene)
Google search answer.
FIRST
- Arrow from C=C to δ+ H
-Arrow from Br-Br to δ- Br
INTERMEDIATE 1
- H bond with C
- No more double bonds
- Carbocation shown by C⁺
- Bromide ion show by Br⁻ with outer electrons shown.
[OR] INTERMEDIATE 2
- H bond with OTHER C
- No more double bonds
- Carbocation shown by C⁺
- Bromide ion show by Br⁻ with outer electrons shown.
LAST 1
- 1-bromopropane drawn.
[OR] LAST 2
- 2-bromopropane drawn.
Alkene monomers join to form _______.
Addition polymers.
What happens when monomers form an addition polymer?
The double bond is opened.
Draw the addition polymerisation of poly(propene)
Google search answer.
- Repeated unit drawn in brackets.
- The double bond breaks to form two single bonds extend beyond the brackets.
- the number, n, is shown outside of the brackets
What are proporties of poly(alkenes)?
- Saturated
- Non-polar
- Unreactive
(thus don’t degrade well in landfills)
Why are alkanes good fuels?
They can burn in oxygen completely.
They burn readily to produce large amounts of energy.
Longer chains = more energy
Show the equation fort he complete cobustion of butane?
C₄H₁₀(g) + 6.5O₂(g) → 4CO₂(g) + 5H₂O(g)
[Same for cycloalkanes, alkenes and alcohols]
What do greenhouse gases do to IR?
Absorb it.
Summarise the greenhouse effect?
- EM radiation from the sun reaches the earth and is absorbed.
- Some is re-emmitted as IR.
- These get absorbed by greenhouse gases and re-emmitted back down to earth.
List the greehouse gases?
Carbon Dioxide.
Water Vapour.
Methane.
Nitrous Oxide.
How have humans contributed to the enhanced greenhouse effect?
- Burnig fossil fules.
- Landfills.
When does incomplete combustion happen?
Burning with a limited oxygen supply.
What is produced when alkanes ar burnt incompletely?
Carbon monoxide.
Carbon particulate.
Show the equation fort he incomplete cobustion of butane producing carbon monoxide?
C₄H₁₀(g) + 4.5O₂(g) → 4CO(g) + 5H₂O(g)
[Same for cycloalkanes, alkenes and alcohols]
How can carbon monoxide be removed?
By using a catalytic converter.
What do unburnt hydrocarbons and the oxides of nitrogen contribute to?
Photochemical Smog in the toposphere.
How do the burning of fossil fules cause cause acid rain?
Burning of fossil fules prodes sulfur dioxide and oxides of nitogen.
This reactsd with water in the atmosphere to form sulfuric and nitric acid.
What is wet scrubbing?
Spraying alkiline CaCO₃ or CaO on acidic gases to neutralise them in flue gases.
What metals are found in catalytic converters?
Platinum.
Rhodium.
(Iridium or palladium).
What harmful gases are converted into what less harmful producs?
HARMFUL
- Carbon Monoxide
- Oxides of Nitrogen
- Unburnt Hydrocarbons
LESS HARMFUL
- Water Vapour
- Nitrogen
- Carbon Dioxide
Why is Solar, wind and wave energy nearly carbon neutral?
CO₂ emmited through manufacturing.
What is the product of a hydrogen fules cell?
Water.
What are the problems with hydrogen fule cells?
- Hydrogen is difficult to store and transport.
- Hydrogen is flamible.
- Hydrogen has a low enrgy:volume ratio.
Undert the same conditions what is simlar for gases?
They ocupy the same volume of space.
How do you work out the number of moles in a gas?
Volume (dm³)/Molar Gas Volume
What is standard temperature and pressure?
298K (25⁰C)
100kPa (101.3kPa)
What is the molar volume of gas at standard RTP
24dm³mol⁻¹
How would you work out the following question:
How much gas in cm³ is produced when 6.2g of Magnesium reacts with hydrochloric acid at r.t.p?
- Write out equation.
Mg + 2HCl → MgCl₂ + H₂ - Moles of Mg = mass/Mr.
- 2/24.3 = 0.255
- Using ratio work out mol of gas.
Mg:H₂ = 1:1 = 0.255:0.255 - Work out volume from Moles.
Vol = Mol x 24 = 0.255 x 24 = 6.12dm³ - Convert.
- 12dm³ = 6120cm³
How would you work out the following question:
Calculate the total volume of gas produced when 5.6dm³ of Nitrous Oxide (N₂O) decomposes.
- Write out equation.
N₂O → N₂ + 0.5O₂ - Sum moles of gas and express as ratio with reactant.
1: (1+0.5) = 1:1.5 - Express volume as ratio.
- 6:x
- work out x.
- 5 x 5.6 = 8.4dm³
What is the ideal gas equation and what do the values mean?
pV = nRT
p: pressure (Pa) V: Volume (m³) n: Moles (mol) R: Gas Constant (on data sheet) T: Temperatur (K)
How would you work out the following question:
Calculate the volume in cm³ of 0.36 moles of a gas at 100kPa and 298K.
- Rearagne pV=nRT.
V= (nRT)/p - Convert reqired units.
100kPa = 100,000Pa - Plug value into equation.
V = (0.36 x 8.31 x 298) / 100000 = 8.91x10⁻³m³ - Convert in needed.
- 91x10⁻³m³ = 8910cm³
How can we measure the volume of a gas?
Using a gas syringe.
ONLY is one gas is being produced.
What is the enthalpy change of a reation?
The heat change in a reaction at a constant pressure.
What is the symbol and units for enthalpy change?
ΔH
kJmol⁻¹
What is the symbol for enthalpy change in standard state under standard conditions?
ΔHᴼ
ᴼ =⦵
What enthalpy change does an endothermic reaction have?
+ΔH
What enthalpy change does an exothermic reaction have?
-ΔH
When is a reaction endothermic?
When more energy is needed to form bonds than break bonds.
When is a reaction exothermic?
When more energy is needed to break bonds than form bonds.
What is bond enthalpy?
The amount of energy neededto break 1 mole of a bond type in a molecule in the gaseous state.
Why might the bond enthalpy of a C-H bond be an averge?
Becasue bonds of the same type don’t all have the same amount of energy.
Enthalpy Change =
= Energy needed to break bonds - Energy needed to from bonds
What determids bond enthalpy in covalent molecules?
- Atractive forces between poative nulcei and negative electrons
- Rupulsive forces between both posative nuclei and between negative electrons being shared.
- The balence betweenm these opposing forcesd is called the bond length.
- The greater the electron density between atoms. The stronger the attractive force. Thus the atoms are pulled futher towards eachther.
- Leading to a shorter bond and a higher bond enthalpy.
Describe the change in bond enthalpy between:
C-C
C=C
C≡C
As you do down:
- Higher electron density shared.
- Thus shorter bond.
- Thus higher bond enthalpy.
What are the four types of enthalpy change?
in DF only
ᴼ =⦵
ΔᵣHᴼ = Standard enthapy change of reation.
ΔₙₑᵤₜHᴼ = Standard enthapy change of neutralisation.
Δ꜀Hᴼ = Standard enthapy change of combustion.
ΔfHᴼ = Standard enthapy change of formation.
What is the standard enthapy change of reation?
The enthalpy change of a reaction acording to the molar quantities in the equation under standard. conditions.
What is the standard enthapy change of neutralisation?
The enthalpy change when an acid and alkali react to form 1 mole of water, under standard conditions.
What is the standard enthapy change of combustion?
The enthalpy change when 1 mole of a substance is completely burned in oxygen to make CO₂ and H₂O, under standard condtions.
What is the standard enthapy change of formation?
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions.
What is Hess’s Law?
The total enthalpy change of a reaction is independent of the route taken.
How do you construct a Hess’s cycle for formation?
IF GIVEN REACTION DATA:
- Reactants → Products
with the arrow being Δ꜀H or ΔᵣH - Balance equations.
- Element in standard states below.
- Arrow from element to reactants and products (both going up) (these are ΔfH)
How do you construct a Hess’s cycle for combustion?
IF GIVEN COMUSTION DATA:
- Reactants/Elements → Products
with the arrow being ΔfH or ΔᵣH - Balance equations.
- Combustion broducts below (CO₂ + H₂O).
- Arrow from reactans/element and products to cobustion products. (both going down) (these are Δ꜀H)
What is calorimetry used for?
Used to work out the enthalpy change of combustion.
Describe the process of calorimetry?
- Weigh mass of fule.
- Set up metal can of water with thermomether over the fule.
- Add lid and wind shield to prevent heat loss and draught movign the flame.
- Once water has increased by a spesific amount weigh fule.
- plug data into q=mcΔT
What is the calorimetry formula?
q=mcΔT
q: energy loss or gained (J)
m: mass (g)
c: Specific heat capacity (4.18 for water)
ΔT: Change in temperature
How would you work out the following question:
100g of water was heated from 23⁰C to 57⁰C by 1.8g of ethanol. Calculate the energy transferred and hence the enthalpy change of the fuel.
- Pulg into q=mcΔT
q= 100 x 4.18 x 34
q = 14212J - Convert to kJ
14212J = 14.212kJ - Work out moles of ethanol with Moles = mass/Mr.
Moles of ethanol = 1.8/46 = 0.039 mol - Work out enthalpy change (energy change per mole).
[negative because it’s exothermic]
-14.212/0.039 = -364.4 kJmol⁻¹
How do catalyst effect the rate of reaction?
- Increases the rate of reaction by providing an alternative pathway that has a lower activation energy.
- The catalyst is chemically unchanged at the end of the reaction.
What is cracking?
Breaking down longer hydrocarbons into higher demand shorter hydrocarbons.
What are heterogeneous catalysts?
The catalyst is in a different state to the reactants.
Why are catalyst used in industry?
To lower the temperature needed for a reaction. Thus less energy is needed so less money is spent.
Speed up th reaction by providing an alternative pathway for the reaction to proceed.
What are the environmental benefits of using catalysts?
Lower temperatures and pressures means less energy is used so less CO₂/Polutatns are used/produced.
Less waste is produced as it allows you to use reactions with better atom economies.
What happens to substances on the surface of solid heterogeneous catalysts?
They are aDsorbed
Describe the reaction that occurs on solid heterogenoues catalsys.
- The reactants bond with the surface of the catalyst (adsorbtion).
- The bonds in th reactatns weaken and break to from readicals.
- The radicals react with eachother to make new substances.
- The new molecules are then released from the surface of the catalyst (desorption).
What can happen to a heterogeneous catalyst to mean it has a reduced effeciveness?
They can be poisoned.
E.g. Lead poisons platinum catalsyst in a catalytic converter in a car.
Waht does saturated mean?
No C=C bonds.
What is the general formula for alkanes?
CₙH₂ₙ₊₂
What is the general formula for cycloalkanes?
CₙH₂ₙ
Why are alkenes reactive?
They have a high electron density.
What are arenes?
A group of organic molecules with benzene ring structures.
What can be call compounds that are arenes?
Aromatic compounds.
opposite are aliphatic compound
How are electrons in benzene delocalised?
The electrons in the double bonds are not attach to any particular carbon.
Thus they are delocalised.
Shown by a circle in a 6 carbon skeleton.
What are the prefix/suffix’s for the following homologous series?
Alkanes Alkanes (branches) Alkenes Alcohols Arenes Halogenoalkanes Cyvloalkanes
Alkanes
-ane
Alkanes (branches)
alky-
Alkenes
-ene
Alcohols
-ol
Arenes
-benzene
Halogenoalkanes
fluoro-/chloro-/bromo-/iodo-
Cyvloalkanes
cyclo- -ane
What shape do alkanes form around a carbon?
Tetrahedral
- therfore they zig-zag.
What shape do alkenes form around a carbon=carbon bond?
Trigonal Planar
- therfore they zig-zag.
What is a sigma (σ) bond?
When two orbitals overlap, and align horizontally to give a single covalent bond.
What is a pi (π) bond?
The parallrl overlap of 2 p orbitals.
Why are π bonds weaker than σ bonds?
The electron density is spread out above and below the nuclei.
Thus the electrostatic attraction between the negative electrons and the posative nuclei is weaker.
This result is a weaker bond and bonf enthalpy.
What is the molecular formula fro ethane?
C₂H₆
What is the shortened structural formula for Butan-1-ol?
CH₃CH₂CH₂CH₂OH
What are the three types of structural isomerisms?
- Chain.
- Positional.
- Functional Group.
What is chain isomerism?
Same molecular formula but different arrangement of the carbon skeleton.
(Pentane and 2-methylbutane)
- Similar chemical properties.
- Different physical properties.
What is positional isomerism?
Same molecular formula but a different position of the functional group on the carbon skeleton.
(Pantan-1-ol and Pentan-2-ol)
- Different chemical properties.
- Different physical properties.
What is functional group isomerism?
Same molecular formula but a differnt functional group.
(Pent-1-ene and Cyclopentane)
- Different chemical properties.
- Different physical properties.
