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chemistry > reactivity 1.3 > Flashcards

reactivity 1.3 Flashcards

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1
Q

3 things combustion (burning) reactions need

A

fuel, oxygen AND a source of ignition/trigger

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2
Q

why are combustion reactions exothermic?

A

because they occur with the generation of heat and light (in the form of flame)

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3
Q

all metals can _______, but not all metals can ________

A

oxidize, combust

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4
Q

some metals will only combust if they have what?

A

high surface area (i.e. they are finely divided as filings or a powder)

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5
Q

does copper combust? why or why not?

A

no because no flame is formed when it is directly heated in air

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6
Q

what do s-block metals form as they undergo combustion?

A

basic (pH wise) ionic oxides

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7
Q

what is the standard example of more reactive metals that combust in air?

A

magnesium, which burns with a bright white flame

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8
Q

two metals that combust but do not form typical oxides (metal & what they form)

A

sodium forms sodium peroxide Na₂O₂
iron forms iron(II, III) oxide, Fe₃O₄

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9
Q

what do p-block non-metals form when they undergo combustion?

A

acidic covalent oxides

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10
Q

why are many organic compounds used as fuels?

A

because they release relatively large amounts of energy when combusted

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11
Q

why do organic compounds not usually undergo spontaneous combustion?

A

their combustion reactions have a high activation energy

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12
Q

organic compounds commonly used as fuels x2

A

hydrocarbons - esp alkanes AND alcohols

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13
Q

define complete combustion?

A

when fuels (i.e. hydrocarbons/alcohols) are burnt in excess oxygen. all C and H will be oxidized (products CO2 and H2O)

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14
Q

qualities of lower alcohols x2

A

burn with an almost invisible flame AND make good fuels

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15
Q

how can ethanol be produced sustainably?

A

via fermentation of sugars

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16
Q

why do cars that run on ethanol require bigger fuel tanks/to fill up more often?

A

ethanol’s energy density is lower than gasoline

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17
Q

two benefits of blending ethanol with gasoline/diesel

A

increases energy density AND makes it safer in case of a fire (easier to see flames)

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18
Q

in a bunsen burner how is complete combustion characterized? x2

A

by a blue AND non-luminous flame

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19
Q

incomplete combustions products x2

A

water AND carbon monoxide or carbon

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20
Q

in a bunsen burner how is complete combustion characterized? x1

A

yellow flame

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21
Q

why is carbon monoxide dangerous? x5

A

colourless, odorless, toxic, poisionous AND binds to haemoglobin in the blood (so it limits its capacity to transport oxygen)

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22
Q

with a very reduced supply of oxygen, in what form will carbon be produced?

A

soot

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23
Q

how can the production of soot can be used to distinguish between different organic compounds?

A

compounds with a higher % of carbon content tend to undergo incomplete combustion and produce more soot in the process

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24
Q

fossil fuels contain _____

A

hydrocarbons

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25
Q

coal advantages x6

A

Relatively cheap

Abundant

Long lifespan (compared to other fossil fuels)

Can be converted into liquid fuels and gases

Relatively safe

Products from the combustion of coal have other uses, e.g. ash can be used to make roads

26
Q

oil advantages x4

A

Easy to store and transport in pipelines and tankers

Impurities can be easily removed

Releases a lot of energy per kg( Known as high energy / enthalpy density)

Easily processed (Fractional distillation and cracking are used to produce other useful chemicals, e.g. shorter-chain alkanes and alkenes)

27
Q

natural gas advantages x4

A

Cheapest of the fossil fuels

Easy to store and transport in pipelines and pressurised containers

Large amounts of energy per unit mass (Known as high specific energy)

Relatively clean (Complete combustion of natural gas happens with a blue flame producing minimal to no harmful compounds)
(Does not contribute to acid rain)

28
Q

coal disadvantages x5

A

Combustion produces large amounts of pollution (Carbon dioxide, Sulfur dioxide, Particulates)

Associated with Global warming, Acid rain, Global dimming / visual pollution

Difficult to transport

Issues around mining (Destruction of habitats, Noise pollution, Health of miners, Safety issues)

Potentially radioactive

29
Q

oil disadvantages x5

A

Combustion produces large amounts of pollution (Carbon dioxide, Sulfur dioxide, Carbon monoxide)

Associated with Global warming, Acid rain, Global dimming / visual pollution, Photochemical smog

Uneven worldwide distribution

Oil spills affecting habitats

Safety issues around drilling

30
Q

natural gas disadvantages x5

A

Combustion produces large amounts of pollution (Carbon dioxide)

Associated with Global warming

Expensive and time-intensive to produce

Expensive to store

Safety issues around storage in pressurised containers

31
Q

order of specific energy of different common fuels x8 (low to high)

A

wood, coal, ethanol, biodisel, crude oil, diesel, gasoline, natural gas

32
Q

4 things that happen as the hydrocarbon chain increases

A

increased carbon content (more C/CO/CO2 produced)

stronger LDF = less volatile hydrocarbon

releases less energy per unit mass of fuel

more likely that incomplete combustion will take place

33
Q

why does volume of CO2 fluctuate within a year?

A

photosynthesis removes CO2 from the atmosphere

34
Q

define greenhouse gas

A

a gas that absorbs radiation emitted from the Earth’s surface, trapping it in the atmosphere so that it is not lost to space

35
Q

4 examples of greenhouse gases

A

CO2, methane, nitrous oxides, water vapour

36
Q

sources of atmospheric carbon dioxide

A

Combustion of wood and fossil fuels

Respiration of plants and animals

Thermal decomposition of carbonate rocks

The effect of acids on carbonates

37
Q

steps of the greenhouse effect x4

A
  1. shortwave radiation from the sun strikes the Earth’s surface it is absorbed and re-emitted from the surface of the Earth as infrared radiation
  2. The infrared radiation passes through the atmosphere where some thermal energy passes straight through and is emitted into space
  3. But some infrared radiation is absorbed by greenhouse gases and re-emitted in all directions
  4. This reduces the thermal energy lost into space and traps it within the Earth’s atmosphere, keeping the Earth warm
38
Q

3 main biofuels

A

bioethanol, biodiesel, biogas

39
Q

what are organic compounds (used for biofuels) produced from?

A

biological carbon fixation

40
Q

how is bioethanol produced?

A

via photosynthesis (fermentation of glucose)

41
Q

what is biodiesel made from?

A

renewable vegetable oils (Natural triglyceride oils are converted to esters of methanol, which makes them less viscous)

42
Q

how does transesterification work?

A

the triglyceride is converted into the less viscous fatty acid methyl ester (FAME) using methanol (acid protonates carbonyl group) (alkali deprotonates alcohol/methanol)

43
Q

what is more commonly used to catalyse the reaction in transesterification?

A

an alkaline catalyst such as NaOH / KOHAcids and alkalis

44
Q

is transesterification reversible?

A

yes

45
Q

what is biogas?

A

a renewable fuel that is released when organic matter, such as food or animal waste, is broken down by microorganisms in the absence of oxygen

46
Q

what does biogas contain?

A

mainly methane and CO2 BUT can also have small amounts of hydrogen sulphide & other chemicals

47
Q

advantages of biofuel x4

A

Carbon neutral, renewable and sustainable if crops / trees are replanted

Reduce greenhouse emissions / pollution

Biodiesel and biogas can reduce the amount of waste going to landfill sites as the waste can be used to produce them

Biofuel production could provide money for less developed countries as they have the space to grow the crops required

48
Q

define fuel cell

A

an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode

49
Q

disadvantages of biofuel x4

A

High costs (Conversion of engines and machinery to run on biofuels instead of petrol / diesel AND Harvesting and transportation)

Many developed countries don’t have the space to be able to produce enough plants to make biofuels because the land is needed for food production (This can lead to deforestation in an effort to meet the demand)

Removes nutrients from the ground / uses large amounts of fertilizers and pesticides

Biofuels typically have lower specific energy than fossil fuels

50
Q

how do fuel cells work?

A

As the fuel enters the cell it becomes oxidised which sets up a potential difference or voltage within the cell

51
Q

different _____ and ______ can be used to set up different types of fuel cells

A

electrolytes AND fuels

52
Q

what is an important fuel cell

A

hydrogen-oxygen

53
Q

a hydrogen fuel cell consists of …. x4

A

a reaction chamber with separate inlets for hydrogen and oxygen gas

an outlet for the product - water

an electrolyte of aqueous sodium hydroxide

a semi-permeable membrane that separates the hydrogen and oxygen gases

54
Q

advantages of hydrogen fuel cells x4

A

Water is the only reaction product, so fuel cells present obvious environmental advantages over other types of cells

The reaction is the same as hydrogen combusting in oxygen, but since the reaction takes place at room temperature without combustion, all the bond energy is converted into electrical energy instead of heat and light

There are no harmful oxides of nitrogen produced, which are usually formed in high-temperature combustion reactions where air is present

Fuel cells have been used on spacecraft, where the product can be used as drinking water for astronauts

55
Q

disadvantages of hydrogen fuel cells x5

A

Hydrogen is a highly flammable gas and the production and storage of hydrogen carries safety hazards

Very thick walled cylinders and pipes are needed to store hydrogen which has economic impacts

The production of hydrogen is a by-product of the crude oil industry, which means it relies on a non-renewable, finite resource

Until a cheap way is found to make hydrogen, its widespread use in fuel cells will be limited

Hydrogen has high energy density, that is, the amount of energy contained in 1g of the fuel is high compared to other fuels, but because it is a gas, its energy density per unit volume is low which means larger containers are needed compared to liquid fuels

56
Q

one difference between fuel cells and other cells

A

the fuel cell operates continuously as long as there is a supply of hydrogen and oxygen; the energy is not stored in the cell.

57
Q

how is a methanol fuel cell different from a hydrogen fuel cell?

A

the methanol fuel cell uses methanol as the course of hydrogen ions and produces carbon dioxide and water while releasing energy (the fuel or source of hydrogen ions, H+, is methanol rather than hydrogen)

58
Q

a methanol fuel cell contains … x4

A

a reaction chamber with separate inlets for methanol and oxygen

outlets for the carbon dioxide and water products

an electrolyte, typically a proton exchange membrane

a semi-permeable membrane that separates the hydrogen and oxygen gases

59
Q

how to find the overall reaction of a hydrogen fuel cell based on two half equations?

A

The overall reaction is found by combining the two half equations and cancelling the common terms

60
Q

how to find the overall reaction of a methanol fuel cell based on two half equations? x3 steps

A

Multiplying the O2 equation by 1.5

Combining the two half equations

Cancelling the common terms

61
Q

advantages of methanol fuel cells over hydrogen fuel cells x5

A

Methanol is easier to store and transport than hydrogen

The fuel cell does not require high pressure or temperature

The membrane has a longer lifespan as it is operating in an aqueous environment

Methanol has a greater energy density (energy per unit volume) than hydrogen

Methanol can be produced from renewable resources through fermentation (This means that methanol is cleaner than hydrogen because its production has less impact on the environment in terms of greenhouse gases.)

62
Q

disadvantages of methanol fuel cells over hydrogen fuel cells x6

A

Methanol is very toxic and highly flammable

Methanol is most commonly made from non-renewable fossil fuels

The fuel cell produces a lower voltage / lower power per unit mass of the cell

The fuel cell has a low efficiency because methanol can pass through the available membrane materials

The reaction at the anode requires a more highly efficient catalyst that contains expensive precious metals, usually ruthenium and palladium

The fuel cell produces the greenhouse gas, carbon dioxide

chemistry (8 decks)

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