Developing Fuels

Question 1

Standard conditions?

Answer 1

RTP stands for ‘room tempreture and pressure’.

Temp - 298K (25 degrees celsius),

Pressure - 100kpa,

If aq solutions are used, conc must be - 1 mol dm-3

All chemicals must be in standard states - states they would be under standard conditions.
E.g. Carbon must be a solid, hydrogen must be a gas and water must be liquid.

Question 2

Formula for working out number of moles at RTP?

Answer 2

number of moles = volume in dm3 / 24,

or,

number of moles = volume in cm3 / 24000.

E.g. how many moles are there in 6.0dm3 of oxygen gas at RTP?
6 / 24 = 0.25 mol.

Question 3

How to work out gas volumes using a balanced equation?

Answer 3

You can work out the amount of gas produced in a reaction using the balanced equation.

This can be done before an experiment, to see how large the apparatus needs to be.

E.g. what volume of gas is produced when 16g of sodium is reacted with excess water at RTP?

Excess water means all the sodium will react.

2Na + 2H2O —> 2NaOH + H2

Ar Na = 23
Moles = mass / ar.
16g / 23 = 0.696

From equation, we know 2 moles of Na produces 1 moles of H2.

So 0.696 / 2 = 0.348 of H2.

So volume of H2 = 0.348 x 24 = 8.35dm3 (use volume in dm3 = moles x 24dm3).

Question 4

10dm3 of methanol vapour is burned in 12dm3 of oxygen. What volume of each reactant and product will be present at constant temperature and pressure?

2CH3OH + 3O2 + 2CO2 + 4H2O?

Answer 4

2CH3OH + 3O2 + 2CO2 + 4H2O

From the equation, we know that 2 moles of methanol react completely with 3 moles of oxygen.

This means that 10dm3 of methanol reacts completely with (10 / 2 = 5. 5 x 3 = 15dm3 of oxygen.

Methanol is therefore in excess in the reactants.

12dm3 of oxygen reacts completely with (12 / 3 = 4. 4 x 2 = 8dm3) of methanol, so 2dm3 of methanol is left over.

2 moles of methanol produces 2 moles of CO2 and 4 moles of water vapour. Therefore, 8dm3 of methanol will produce (8 / 2 = 4. 4 x 2 = 8dm3) of CO2 and (8/2 = 4. 4 x 4= 16dm3) of water vapour.

So once the reaction is complete, there will be 2dm3 of methanol, no oxygen, 8dm3 of carbon dioxide and 16dm3 of water vapour.

Question 5

Ideal gas equation?

Answer 5

This is used to find the number of moles in a certain volume at any temperature and pressure (not just RTP).

pV = nRT.

p - pressure (Pa)
V - volume (m3)
n - number of moles
R - 8.314 (J K-1 mol - 1) (gas constant is on data sheet)
T - temperature (K).

Question 6

Conversions?

Answer 6

K = Celsius + 273

1cm3 = 1x10-6 m3

1dm3 = 1 x10-3 m3

Jmol-1 / 1000 = KJmol-1

1cm3 = 1g

Question 7

How to use a gas syringe?

Answer 7

Attach gas syringe to the opening of a reaction vessel (usually a bung in a conical flask(.

This will show total volume of gas produced.

If more than one gas is given off, it won’t show how much of each there is. So you can work this out using balanced equation like on previous flashcard.

Really vigorous reactions can blow the plunger out so be careful.

Question 8

Enthalpy change?

Answer 8

When chemical reactions happen, some bonds are broken and some are made. This causes a change in energy.

Enthalpy change (🔺H) is the heat energy transferred in a reaction at a constant pressure. Units of delta H are KJ mol-1.

You can find the enthalpy change through experiments or in data books (usually under standard conditions).

You write 🔺H with a little circle next to it to show enthalpy change under standard conditions.

Question 9

Enthalpy definition?

Answer 9

Heat energy stored in a chemical system (chemical potential energy).
It can’t be measured directly.

However, we can measure energy absorbed/released to surroundings.

Question 10

Exothermic and endothermic?

Answer 10

Exothermic - give out energy so the 🔺H is negative.

Oxidation is usually exothermic (like combustion of methane and oxidation of carbohydrates).

Endothermic - take in energy so the 🔺H is positive.

The thermal decomposition of calcium carbonate is endothermic and the main reactions of photosynthesis are SLO endothermic.

Question 11

Calculating enthalpy changes?

Answer 11

You need energy to break bonds - this is endothermic.

Energy is released when bonds are made - this is exothermic.

The enthalpy chnage is the overall effect of these two. If you need more energy to break bonds than I’d released when bonds are made, the 🔺H is positive.

Stronger bonds have higher bond enthalpies.

Enthalpy change of reaction = totally energy absorbed to break bonds - total energy released by making bonds.

Average bond enthalpies are published in data books to help calculate them. You might be asked to work enthalpy out by getting a small chart with the bonds and then the average bond enthalpies and a balanced equation.

Question 12

Calculate the overall enthalpy change for this reaction: N2 + 3H2 —> 2NH3.

N—-N = 945kJ mol-1
H-H = 436KJ mol-1
H-N = 391KJ mol-1

Answer 12

The amount of bonds broken is the reactants.

So 1 N—-N bond is broken = 945
3 H-H bonds are broken = 1308.
Add them = 2253.

Then the amount of bonds formed is the products.

So 6 N-H bonds are formed = 2346.

2253 - 2346 = -93 so the reactions is exothermic.

Question 13

Average bond enthalpies are not exact?

Answer 13

Water has two O-H bonds but the amount of energy needed to break each of them are different.

Average bond enthalpies are actually the energy needed to break one mole of bonds in the gas phase, average over many different compounds.

Question 14

How is bond enthalpy related to bond length?

Answer 14

In covalent molecules, the positive nuclei are attracted to the shared electrons.

There isn’t just an attraction between the nuclei and the shared electrons. The two positively charged nuclei also repel each other, as do the electrons.

The distance between the two nuclei is the distance where the attractive and repulsive forces balance eachother.

The stronger the attraction between the atoms, the higher the bond enthalpy and the shorter the bond length. If there’s more attraction, the nuclei are pulled closer.

So, double bonds have a greater enthalpy and shorter length. Triple bonds have an even greater enthalpy and shorter length.

Question 15

Enthalpy profile diagram?

Answer 15

Reactants have high enthalpy and products have a lower enthalpy = enthalpy change is exothermic. Heat is lost to surroundings.

Reactants have low enthalpy and products have a higher enthalpy = enthalpy change is endothermic. Heat is lost from surroundings.

🔺H is the arrow from the products to the reactants.

Activation energy (Ea) is the little bump on the graph. This is required to break the bonds in the reactants and so the reaction can proceed. 
E.g. a match doesn’t strike on its own. 

The less enthalpy a substance has, the more stable it is.

Question 16

Determining the 🔺H of a reaction using calorimetry?

Answer 16

Insulated beaker (polystyrene cup with lid on and thermometer in).

We measure the temperature of the solution inside the cup.

E.g. Mg + CuSO4 —> MgSO4 + Cu

The Mg is in excess because we are measuring the temperature chnage of the solution (CuSO4) and we need to make sure the CuSO4 is fully reacted.

Record the cm3 and concentration of the solution your measuring the temperature change of.

Work out moles (m = c x v).
Record the initial temperature of the solution.
Add the Mg in excess.
Record the highest temperature produced.
Work out the change in temperature.

Use calculation: q = mc🔺T
The m should be 100, I think.

Then rearrange the equation.
🔺T = -q / mol (-q is used for exothermic and q is used for endothermic).

Question 17

Finding the enthalpy change of a reaction with two solutions?

Answer 17

In a neutralisation reaction, you will be given 2 aq solutions to react.

Record concentrations and volumes of both the solutions.

Work out moles.

Use a closed, polystyrene cup and thermometer. Closed system.

Record the initial temperatures of both the solutions. Record maximum temperature when you react the solutions together.

Record the change in temperature.

Use calculation: q = mc🔺T
Mass of solution should be combined mass of both the solutions (50).

Then rearrange the equation: 🔺H = -q / mol (-q is used for exothermic and q is endothermic).

Question 18

Determining the enthalpy change of combustion using calorimetry?

Answer 18

Insulated beaker (metal can or glass beaker). There should be a lid on.

Inside should be a known vol of water. We use density to calculate mass of the water.

Record temperature of water.
Record mass of the thing being burnt. Burn the thing under the metal can/glass beaker. The mass of the water will drop because it’s being evaporated.

Record new mass of thing being burnt and temperature of water.

Record change in temperature and change in mass of the thing being burnt.

Use calculation: q = mc🔺T
M is just the amount of grams.

Then use 🔺T = -q/q / mol.

Question 19

Standard enthalpy change symbols?

Answer 19

Standard enthalpy change of a reaction is 🔺rH(circle) - this is the enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions.

Standard enthalpy change of formation is 🔺fH(circle) - this is the enthalpy change when 1 mole of compound is formed from its elements in their standard states, under standard conditions.

Standard enthalpy change of combustion 🔺cH(circle) - enthalpy chnage when 1 mole of substance is completely burned in oxygen under standard conditions.

Question 20

Enthalpy change equation?

Answer 20

q = mc🔺T

q = energy in joules
m = mass of solution that we recorded temperature change of (in g)
c = specific heat capacity (energy needed to raise temperature of 1g of solution by 1 degrees Celsius). 
🔺T = temperature change.

Question 21

Why is our value lower than the book value for 🔺H?

Answer 21

Heat loss.

Possibility of an incomplete combustion.

Non-standard solutions man have occurred (thermometer may not be accurate).

Question 22

Working out standard enthalpy change of reaction?

Answer 22

🔺Hr(circle),

Question 24

Determining the enthalpy change of a neutralisation reaction?

Answer 24

You’ll be given an equation. Make it an ionic equation and balance it.

Record the initial temperature of the acid.
Record vol and conc of both of the solutions too.

Work out moles.

Put them both in a polystyrene cup (inside of a glass beaker).

Record the max temperature reached of the acid once the alkali has been added.

Work out the chnage in temp. If the chnage is temp is small, use a higher concentration of the acid and alkali.

Use calculation: q = mc🔺T (q should always be in KJ).

And then use 🔺T = -q/q / mol.

Question 25

What compounds burn to give carbon dioxide?

Answer 25

When you burn an alkane completely in plenty of oxygen, you get CO2 and water (in the form of steam).

CH4 + 2O2 —> CO2 + 2H2O

Combustion of alkanes is very exothermic and therefore, alkanes make great fuels.

Cycloalkanes, alkenes and alcohols react in a similar way. The products are also carbon dioxide and water.

Question 26

Combustion of cycloalkanes, alkenes and alcohols?

Answer 26

Cycloalkanes: C4H8 + 6O2 —> 4CO2

Alkenes: C4H8 + 6O2 —> 4CO2 + 4H2O

Alcohols: CH3OH + 1,1/2O2 —> CO2 + 2H2O

These are exothermic - can be used for fuels too.

Question 27

Carbon dioxide is a green house gas?

Answer 27

The earth naturally radiates infrared radiation into space.

Some greenhouse gases (water vapour, CO2 and methane) absorb some of this radiation, keeping the earth warm. This is called the greenhouse effect.

Burning carbon-based fuels increased the CO2 in the atmosphere, this is the ‘enhanced greenhouse effect’ also known as global warming.

This causes the earth to earn up slowly - huge problem. Has effects like melting of poplar ice caps.

Controlling this global warming is not easy.

Question 28

Carbon monoxide formation?

Answer 28

If there’s not enough oxygen, organic compounds combust incompletely and you get carbon monoxide instead of carbon dioxide.

Alkanes: CH4 + 1,1/2O2 —> CO + 2H2O

Cycloalkanes, alkenes and alcohols equations r all the same but with CO in place of CO2.

Question 29

What is smog?

Answer 29

Engines don’t burn all the fuel molecules. Some of them come out as unburnt hydrocarbons.

Oxides of nitrogen (NOx) are produced when high pressure and temperature in a car engine cause the nitrogen and oxygen in the air to react together.

The hydrocarbons and nitrogen oxides react in the presence of sunlight to form ground-level ozone (O3).

This is a component of photochemical smog, which irritates eyes, aggravated respiratory problems and can cause lung damage.

Question 30

How is acid rain made?

Answer 30

Burning Gossy me fuels that contain sulfur causes acid rain.

The sulfate brine to produce sulfur dioxide gas which then enters the atmosphere, dissolves in the moisture and then is converted to sulfuric acid.

This same process occurs when oxides of nitrogen (NO) escape into the atmosphere - nitric acid forms.

Acid rain destroys trees and vegetation, and corrodes buildings. Kills fish too.

Question 31

Particulates cause health issues?

Answer 31

Any tiny particles of liquid suspended in the air (such as acid droplets in rain) are particulates.

Sold particles like carbon, are also produced burning fossil fuels in vehicles and power stations.

These can settle in peoples lung and cause problems such as decreased lung function and irritation in the airways.

They also contribute to cardiovascular problems which lead to heart attacks and strokes.

Question 32

Fossil fuels are renewable?

Answer 32

The three fossil fuels (coal, oil and natural gas) are major fuels.

They’re relatively easily extracted and produce large amounts of energy when burnt.

There’s a finite amount of them.

Oil will be the first to go - and get more expensive because of it.

It’s not sustainable to keep using fossil fuels.

Question 33

How to manage issues with fossil fuels?

Answer 33

• Cause health issues and global warming.
• Transport, industry and power generation are biggest sources of air pollutants.

To reduce these issues, we:

• Particulates are removed from power station flue gases using calcium oxide. Flue gases are the emissions from industrial exhausts and chimneys.
• Particulates are removed from power stations using wet scrubbers (capture them in water droplets) and from other car exhausts using filters.
• Catalytic converters reduce CO, unburnt hydrocarbons, sulfur dioxide and nitrogen oxide from vehicles.
• Oxygenates are now added to petrol to reduce CO - they help the fuel to fully combust.
• Carbon dioxide emissions are high because our electricity comes from burning fossil fuels and cars are increased on roads.
• We can also develop new fuels.

Question 34

Methods to reduce pollution?

Answer 34

• Governments can change laws to reduce pollution. E.g. UK sulfur and NO emissions from power stations have been reduced as laws have been tightened.
• New vehicles are not allowed to pollute above a certain level, and the yearly MOT includes an emission test. Catalytic converters have been compulsory since 1992 in UK.
• Governments can tax pollution more highly. E.g. raising taxes on fuel or high polluting engines.
• People can make fewer car journeys, take public transport, etc.

Question 35

Renewable fuels?

Answer 35

Wind, solar and wave power,

Biofuels,

Hydrogen.

Question 36

Wind, solar and wave power?

Answer 36

Renewable and carbon neutral (dont add to greenhouse gases or other pollution into the atmosphere).

CO2 is given out though.

Weaknesses:

• they’re not reliable because we rely on wind or sun.
• takes a lot of wind turbines, solar pancake or wave energy collection to even get a fraction of energy currently supplied by fossil fuels.

Question 37

Biofuels?

Answer 37

Fuels made from living matter over a short period of time.

Bioethanol - ethanol made by fermentation of sugar from crops such as maize.

Biodiesel - refining renewable fats and oils such as vegetable oil.

Biogas - breakdown of organic waste matter.

These fuels produce CO2 when they’re burnt, bits it’s CO2 that the plants absorbed while growing so they’re carbon neutral.

But CO2 is given out while refining and transporting the fuel as well as making the fertilisers and powering agricultural machinery used to grow and harvest crops - so are they really carbon neutral?

Biodiesel and biogas can also be made from waste that would otherwise go to landfill.

Weaknesses:

• Switching from fossil fuels to biofuels in transport means that the petrol car engines would have to be modified to use fuels with high ethanol concentration.
• The land used to grow crops for fuel can’t be used to grow food - developed country’s like the Uk will create a huge demand as they try to find fossil fuel alternatives. Poorer developing countries could use this as a way of earning money - this means they won’t grow enough food to actually eat.

Question 38

Hydrogen as fuel?

Answer 38

Hydrogen gas can either be burned in a modified engine, or used in a fuel cell.

A fuel cell converts hydrogen and oxygen into water which produces electricity.

Water is the only waste product.

Hydrogen can be obtained from seawater - but this takes energy to extract it. This is why it’s more accurate to think of hydrogen as an energy carrier rather than an energy source.

The method used to extract hydrogen determines how environmentally friendly the fuel is - if the energy is renewable, then hydrogen as fuel will be carbon neutral (except for the carbon emitted).

Weaknesses:

• Transporting and storing hydrogen is hard cause it’s flammable and it needs to be liquified due to the low energy to volume ratio of hydrogen gas.
• This also means building a whole new fuel supply infrastructure (chemical plants to produce the hydrogen fuel, a network of refuelling stations).

Question 39

How to choose an energy strategy?

Answer 39

We need more energy cause the population is growing and climate chnage is a huge issue. More countries are becoming richer too and they want energy sources.

The UK needs to make decisions about whrtr to get energy from.

The UK needs to ensure ‘energy security’ - make sure that they have enough clean, affordable energy. This is difficult because there’s increasing competition for available supplies as countries become more industrIal, which means higher prices.

Also hard because supplies are disrupted due to various political issues (such as unstable or unfriendly governments or terrorism).

Question 40

How does the UK ensure energy security?

Answer 40

• Encourage public and industry to become more energy efficient.
• Continuing to use our coal, oil and gas reserves.
• Creating financial incentives to reduce CO2 emissions (for example, carbon capture and storage technology reduces CO2 emissions - burgs CO2 before it reaches atmosphere). Financial incentives make it more attractive for business to develop this kind of technology (pay for each tonne of carbon they emit).
• Use more renewable energy.
• Encourage research of nee energy sources.

The decisions could be different for different countries. E.g. Brazil has few oil restocked but it does have large amounts of land and a good climate so biofuels could be a good idea.

Question 41

How is carbon monoxide poisonous?

Answer 41

It is produced in the incomplete combustion of carbon-based fuels (mainly in car engines).

It’s poisonous.

CO are chemically and physically similar to oxygen molecules. This means they bind with the same sites on haemoglobin molecules.

CO is better at binding to haemoglobin than oxygen, so less oxygen can be carried around the body. This means that if people breathe in too much CO, they can die from internal suffocation.

Question 47

Hess’s law?

Answer 47

The law says that the total enthalpy change of a reaction is always the same, no matter which route is taken.

This law is handy for working out enthalpy chnage that you cannot find directly by doing experiments.

Diagrams are called enthalpy cycles and sometimes called Hess cycles. They show all the routes.

On a reaction and products diagram, the enthalpy chnage for both reactions will be the same, even if there is an intermediate involved. This is shown in the video you watched.

Question 47

Catalysts?

Answer 47

A catalyst increases the rate of reaction by providing an alternative pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction.

Catalysis - speeding up a chemical reaction using a catalyst.

They are usually remade at the end of a reaction.

Iron in the Haber process:
N2 + 2H2 <> 2NH3

For is on the double arrow.

Question 47

Catalysts are used in cracking?

Answer 47

Short chain hydrocarbons tend to be more useful than longer ones and so cracking breaks them down. To smaller ones (including alkenes).

Hexadecane C16H34 —> C7H14 + C9H20 (heptane and nonane).

The products of cracking are read on and the same molecule can give different cracking products.

Without a catalyst, the cracking process requires extremely high temperatures and pressures which is so expensive.

Hydrocarbon vapour is passed over a heated solid catalyst, cracking takes place at a lower gempteyirr and pressure (around 450 degrees).

Question 47

Heterogeneous catalysts?

Answer 47

They’re in a different physical state from the reactants.

E.g. catalyst is a solid and reactants r liquids.

Examples:

• Iron is used in Haber process as a catalyst. Iron is solid and hydrogen gas and nitrogen gas are reactants.
• Platinum is catalyst used in catalytic converters - which sit queue to in a car exhaust and stop pollutants from coming out.

Without catalytic converters, cars spew out stuff like CO and oxides of nitrogen and unburnt hydrocarbons. When the sun shines on NO and hydrocarbons, low level ozone forms.

CC’s get rid of them by changing them to harmless gases like water vapour and nitrogen, or less harmful ones like CO2.

Question 47

How do reactions occur on heterogeneous catalysts?

Answer 47

Solid heterogeneous catalysts provide a surface for a reaction to take place on.

1. Reactant molecules arrive at the surface and bond with the solid catalysts. This is called adsorption.
2. The bonds between the reactants atoms are weakened and break up. This forms radicals - atoms or molecules with unpaired electrons. These radicals then get together and make new molecules.
3. The new molecules are then detected from the catalyst. This is desorption.