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Chemistry Unit 2 > Unit 2 > Flashcards

Unit 2 Flashcards

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1
Q

What is the empirical formula?

A

The simplest whole number ratio of the number of atoms of each element in a molecule.

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2
Q

What is the molecular formula?

A

The actual number of atoms of each elements present in a molecule.

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3
Q

What is the general formula?

A

The simplest algebraic formula to represent any member of a homologous series.

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4
Q

What is a structural Formula?

A

gives minimal data e.g. CH3CH2CH(OH)CH3

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5
Q

What is a displayed formula@

A

shows all the bonds and atoms present.

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6
Q

What is structural isomerism

A

They have the same molecular formula but have different structural and displayed formulas.

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7
Q

What is stereoisomerism?

A

Compounds with Same structural formula but different arrangement of atoms in space.

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8
Q

What is the Fuctional group.

A

It is a group of atoms found in a compound that are responsible for the characteristic reactions of that compound.

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9
Q

How do you calculate percentage yield?

A

Actual Yield divided by theoretical Yield.

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10
Q

Why might the yield be less that 100%?

A
  • Not all the distillate evaporated.
  • When recrystallising, not all the crystals crystallised from the solution.
  • The reaction did not go to completion.
  • The reciever was not cooled, therefore not all the distillate condensed.
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11
Q

How do you calculate atom economy.

A

molecular mass of desired product divided sum of molecular masses of all products.

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12
Q

Explain Radical substitution.

A

CH4+Cl2====>CH3Cl+HCl

Initiation
Cl2===>2cl* split by uv homolytic fission

Propogation
CH4+Cl====>CH3+HCl
CH3+cl2=====>CH3Cl+Cl chain reaction continues

Termination
CH3+CH3====>C2H6
Cl+CH3=====>CH3CL

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13
Q

Why is petrol a good fuel?

A
  • Its vapour mixes easily with air/oxygen and ignites at low temperature.
  • As a liquid it is easily transported and easy to store
  • it leaves little or no residue after it has burned.
  • When it burns it releases alt of energy.
  • the structures of the hydrocarbons can be changed so it burns more steadily and smoothly.
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14
Q

How are the components of crude oil seperated?

A

Fractional distillation

  • components of crude oil is seperated on a fractioning column on the basis of their different boiling points.
  • The heavier fractions, with high boiling points condense first and come off lower down the column.

Cracking
*cracking uses high temperature and a catalyst to break up longer chains into alkenes and either more useful shorter alkanes (used as fuels) or hydrogen. This is a form of thermal decomposition.

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15
Q

How is the octane number reduced?

A

Straight chain alkanes ignite prematurely and cause knocking.

  • Use a cataly to convert straight chain alkanes into branched chain alkanes.
  • High temp and catalyst used to convert straight chain alkanes into cycloalkane and hydroger.
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16
Q

Give examples of alternative fuels.

A
  • Biogas made from the anaerobic digestion of waste material, such as animal manure and dead plants.
  • Biodiesel produced from vegetable oil, is a substitute for diesel.
  • alcohols such as ethanol can be made from weat corn and sugar.
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17
Q

Explain the shape and bonding of Alkenes?

A

The sigma bond lies along the axis between the C=C bond.
The pi bond lies above and below the plane of the flat alkene molecule.
The pi bonds do not contribute to the shape, therefore trigonal planar and bond angle is 120degrees.

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18
Q

Explain the reactions of alkenes?

A

The pi bonds produce two regions of high electron density in the molecule, this attracts positive ions or even induces dipoles in some molecules.
*They undergo electrophilic addition.

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19
Q

What is an electrophile?

A

Electron pair acceptor.

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20
Q

How do you get rid of the double bond?

A

H2, Nickel catalyst and heat

CH3CH=CH===>CH3CH2CH3

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21
Q

How do you convert an alkene into an alcohol?

A

Steam, acid catalyst and heat and high pressure

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22
Q

What is the test for alkene?

A

Add bromine water in the dark, the bromine changes from orange to colouless as an addition product is formed.

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23
Q

How are addition polymers formed?

A

Alkenes are monomers,

Ziegler natta catalyst, heat and high pressure.

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24
Q

What are the problems with polymers.

A

They are non polar strong bonds therefore unreactive and persist in the environment causing a litter problem.

  • chemists are now developing biodegradable polymers e.g isoprene in baby nappies.
  • The best way to deal with them is to recyle them, however they are difficult to sepeate. and are of lower quality.
  • Burning them produces toxic products, e.g CO, HCL, is removed by passing the wase gases as spray towers.
  • waste plasics are being used as fuels, can be cracked to give new alkenes.
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25
Q

Explain the physical properties of Alcohol.

A
  • Lower than expected volatility( higher than expected boiling point) because of the strong hydrogen bonding.
  • Short chain alcohols are very soluble in water as they can form hydrogen bonds with water.
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26
Q

Why are alcohols good fuels

A

Availability, ease of use and storage makes alcohols good fuels.

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27
Q

Explain the elimination/dehydration of water reaction.

A

acid catalyst and heat used to remove water molecule and produce alkene and water.

CH3CH2OH======>C2H4+H20

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28
Q

How are esters made?

A

Alcohol + Carboxylic acid======> ester + water

Heat Acid catalyst used e.g H2SO4

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29
Q

What is the test for alcohols?

A

add potassium dichromate goes orange to blue-green.

30
Q

Explain the industrial production of alcohol.

A

*Fermentation of sugars using Yeast
C6H12O6=====>2C2H5OH+2CO2

*Hydration of ethene
ethene, steam 300degrees and high pressure acid catalyst

31
Q

What are the main uses of alcohols?

A
  • Methanol is used to make bakelike and perspex and is used as an additive to improve combustion or fuel.
  • Ethanol used as a solvent for several organic chemicals, fuel for cars in many countries, as a beverage and in the preperation of esters.
32
Q

What reactions do halogenoalkanes mostly undergo?

A

Nucleophilic substitution.

33
Q

What is a nucleophile?

A

Electron pair donor.

34
Q

What is the least reactive and stongest halogenoalkane?

A

C-F

35
Q

What are some uses for halogenoalkanes?

A

CFC’s were once used as refigerants and in fire extinguishers, they are stable and unreactive.

Unsaturated halogenoalkanes can be used to make polymers.e.g. chloroethene

36
Q

How do you compare the reactivities of halogenoalkanes?

A

1add AgNO3 in ethanol at 50 degrees.
2Add few drops of comparable halogenoalkanes.
3*The mixture goes cloudy,the faster the reaction the more reactive. Iodine is quickest therefore bond enthalpy determines the rate of hydrolysis.

37
Q

Why are CFC’s not used any longer?

A

It was discovered that it leads to the depletion of the ozone, now HFC’s are used instead,the C-F bonds are so strong that they do not break, even in the ozone layer.

38
Q

What are some uses of HFC’s?

A
  • Refigerants
  • Fire extinguishers( unreactive so do not burn easily, denser that air so sink and smother fire)
  • Dry cleaning ( good solvent for grease and fats)
39
Q

What does infrared spectroscopy enable us to do?

A

It helps determine the compounds structure.

  • different compounds absorb at different frequencies in the inrared region of the spectrum.
  • Wavenumber is the reciprocal of wavelength.
40
Q

What does mass spectrometry enable us to do?

A

It helps distinguish between isomers.
*positive ions and radicals are producen, the positive ions are detected and analysed according to their mass/charge ratio.

41
Q

What is Enthalpy?

A

The heat energy stored in a chemical system.

42
Q

What in endothermic?

A

Heat energy is gained from its surrounding so deltaH is positive.

43
Q

What is exothermic?

A

Heat energy is lost to its surroundings so deltaH is negative.

44
Q

What are the X and Y axis of an enthalpy profile diagram.

A

X is Course of reaction

Y is Enthalpy

45
Q

What are the standard conditions?

A

Pressure: 100KPa
Temp: 298 Kelvin
Conc of solutions: 1 mol/dm^3

46
Q

What is the equation for calculating enthalpy change in solution?

A

q=mcdeltat

47
Q

What is the standard enthalpy change of formation?

A

Enthalpy change when 1 mole of a compound is formed from its constituent elements.in their standard states, under standard conditions.

48
Q

What is the standard Enthalpy change of combustion?

A

Enthalpy change when 1 mole of a compound completely reacts with oxygen, under standard conditions.

49
Q

What is the standard Enthalpy change of Reaction?

A

The enthalpy change that accompanies a reaction under standard conditions in their molar quantityies.

50
Q

What is average bond enthalpy?

and Why are they calculated

A
  • The average enthalpy change required to break 1 mole of a type of bond by homolytic fission in a gaseous species.
  • Covalent bonds have different strengths., for polyatomic molecules the bond energy for successive broken bonds differ.
51
Q

How do you calculate enthalpy change from average bond enthalpies?

A

(delta H reacrtion)= (delta H reactant)-(delataH product).

52
Q

State hess’ law?

A

For any chemical change the enthalpy change is the same regardless of what route is taken.

53
Q

What is a catalyst?

A

A substance that increases the rate of reaction without being changed or consumed.

54
Q

What is a dynamic Equilibrium?

A

Forward and backward reactions are taking place at equal rates.
*they happen in a closed system.

55
Q

What is la chattliers principle?

A

When a chemical system is subject to change the position of equilibrium shifts to oppose the change.

56
Q

What effect do these have in a dynamic equilibrium?

  • increase temp
  • Increase pressure
  • Increase reactant conc
A
  • Favour the endothermic direction
  • Favour the side with the least moles.
  • Favour the product side.
57
Q

Why is there a compromise between yield and recation rate?

A

Sometimes reaction rate is favoured instead of yield.

58
Q

What is the greenhouse effect?

A

The warming of the earths surface by infrared radiation that is absorbed by gases and then reemitted .
*a steady state system exists in which the rate at which the earth absorbs energy is equal to the energy radiated back into space.

59
Q

What is a greenhouse gas?

A

A gas that lets infrared radiation through but prevents the radiation from leaving.

60
Q

Give examples of some bonds that absorb radiation?

A

C=O O-H C-H

61
Q

What is the greenhouse factor?

A

The ability to absorb infared radiation on a scale where CO2 is 1.

62
Q

Explain global warming?

A

The earths climate is getting warmer due to increased furning of fossil fuels, deforestation increasing CO2 levels.
*Many belive the earths ecosystem will not be able to cope.

63
Q

What are Carbons sinks and how is CO2 removed from the atmosphere?

A

Carbon sinks are natural ways to remove CO2 from the atmosphere and trapping it.

  • Plants remove CO2 by photosynthesis, phytoplankton remove dissolved CO2.
  • CO2 reacts with water hence the seas can act as atmospheric sinks.
  • CO2 is converted into CaCO3 by zooplankton in the oceans, when these die they sink to the bottom of the ocean, thus removing CO2.
64
Q

What are some consequences of Global warming?

A
  • Melting of the polar ice caps will cause an increase in sea levels, therefore dissaperance of huge lands inhabited by humans.
  • CO2 dissolved in water creates an acidic solution which could dissole CaCO3 on coral reefs.
  • More severe weathers due to higher temp. eg hurricanes flooding and storms.
  • desertification of arid regions.
65
Q

How can CO2 emission be reduced?

A

1* reduce use of fossil fuels, use renewable fuels.
2* Carbon capture and storage in power plants.
*CO2 from power stations is seperated from other gases,
compressed and then pumped into deep geological, e.g exhausted gas or oil fields, the CO2 is dossolve onto the coal surface.
*Ocean storage
*The CO2 can be reacted with metal oxides to form solid metal carbonates.

66
Q

How does the ozone absorbe harmful UV rays?

A

UV
O3====>O2+O*
O*+O2====>O3

67
Q

Explain the chemicals that cause the depletion of the ozone?

A

CFC’ produce cl, which catalyses the breakdown of the ozone.
High temp in jet engines and thunderstorms break N=N in N2,
N2 +O2====>2NO

68
Q

What do catalytic converters do?

A

They remove many polutants form waste gases.

  • They have a ceramic honeycomb with a large surface area coated with a solid catalyst (Platinum, Palladium and Rhodium)
  • The reactants form weak bonds for adsorption and desorption. they weaken bonds of the pollutents so a reaction can take place.
69
Q

How many types of converters are there?

A

2
Oxidation for diesel engines
three way catalysts for petrol engines they react with eachother.

70
Q

Green chemistry criteria

A
  • less steps should be favoured
  • renewable energy should be used.
  • Catalysts should be used
  • environmentally friendly solvents
  • Reactions with high atom economy, addition reactions over substitution.
71
Q

Explain some of the roles of international agreements for a greener economy.

A

*Montreal- Bans use of CFCs
*Kyoto limits production of green house gases
*

Chemistry Unit 2 (1 decks)

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