Energy from Fuels

Define biofuels

Biofuels are produced from the fixation of carbon over a short period of time through photosynthesis.

State the equation of complete combustion of ethanol

C2H5OH (l) + 3O2 → 3H2O(l) + 2CO2 (g)

Describe the relationship between the oxygen content of a fuel and its specific energy

The more oxygen, the lower its specific heat capacity because oxygen has a low specific heat capacity.

What are two advantages of coal use over wood

It is the most abundant fossil fuel and has a high specific energy thus it can provide more energy than wood and it is more accessible.

Define the term energy density and what it means that a fuel has a high or low energy density

Energy stored per mass/volume usually in J/kg. High energy density contains a large amount of energy in a small amount of mass/volume (or relative to it) making it incredibly efficient as a fuel source while low energy density needs more of that substance to produce the same level of energy as high energy density substances.

Describe how the composition of fuels change as they are exposed to high pressure

Fuels in high pressure can shift with longer hydrocarbon chains into more lighter, gaseous fuels.

What are the advantages of using wood as a fuel source?

Wood is a renewable source and sustainable fuel.

Define sustainable fuel

Fuels produced from renewable sources (able to be replenished in human lifetime).

What is the difference of renewable and non-renewable fuels?

Renewable fuels are replenished in an average human lifespan while non-renewable fuels can not.

What harmful pollutants are produced when wood is burnt in an enclosed space?

Soot, hydrocarbons, and carbon monoxide are produced due to incomplete combustion because in an enclosed space there is not enough oxygen to combust all of the wood.

What are the differences of incomplete and complete combustion

Complete combustion occurs when there is sufficient amount of oxygen in the atmosphere to combust a substance to produce carbon dioxide and water whereas incomplete combustion occurs due to insufficient amount of oxygen in the atmosphere to combust a substance. This could be because the air is limited or the compound has a high percentage of carbon content. The byproducts are soot (C (s)) or carbon monoxide.

How does the structure of carbon dioxide cause greenhouse gas?

The covalent bonds between carbon and oxygen in carbon dioxide (CO₂) absorb infrared radiation (IR) or low-frequency radiation emitted by the Earth. This absorption occurs due to the way the bonds stretch and bend. When the bonds undergo asymmetric stretching, the carbon-oxygen bond length changes, the bond angle alters, and the molecule's polarity or dipole moment changes. As a result, some of the absorbed energy is re-radiated back towards the Earth's surface, contributing to the greenhouse effect.

State the equation of anaerobic respiration in yeast (fermentation)

C6H12O6 → 2C2H5OH + 2CO2

What are the conditions in order for glucose to undergo fermentation?

Absence of oxygen, below 40˚C in acidic environment because enzymes are needed to catalyze fermentation (too high = enzymes denature), can lower the pH which can help improve the efficiency of the fermentation process.

State the advantages of ethanol as a fuel source

Ethanol is renewable, produces lower emissions of carbon monoxide and nitrogen oxides, and decreases the country’s dependency on oil which contributes to the harmful greenhouse effect.

Disadvantages- It is not as energy-dense as gasoline, more ethanol must be produced, fermentation conditions must be met to produce ethanol

How do fuel cells work?

Fuel enters fuel cell at anode (positive end)
Molecules of fuel splits into protons/electrons by a catalyst
Electrolyte is substance that allows protons to pass through but prevents electrons to pass through
At cathode, oxygen from the air enters fuel cell
Electron travels around electrolyte through a external circuit (energy)
Protons that pass through the electrolyte combines with oxygen
Creates water (no carbon dioxide)

How is methanol used as fuel source?

Methanol is used as an alternative fuel in fuel cells. It has a high energy density and is easy to transport because it is a liquid at normal temperature and pressure. In a fuel cell, methanol is oxidized to form carbon dioxide (CO₂). This reaction with oxygen produces water (H₂O).
Electrons flow from the anode to the cathode through an external circuit, creating electricity.
Water is consumed at the anode and produced at the cathode.
This process generates clean energy with water as the only byproduct.

What are the advantages or disadvantages of fuel cells?

Advantages- High energy efficiency, minimal to no emission to atmosphere
Disadvantages- High cost, safety concerns since hydrogen is a highly flammable gas, limited infrastructure

State the advantages and disadvantages of using biofuel

Advantages- cheap and readily available, if crops/trees are replanted they become a renewable and sustainable source, less polluting than fossil fuels
Disadvantages- Competes with food crops for land and nutrients, uses fertilizers that can harm other organisms, lower specific energy

Define specific energy

Amount of energy stored in per unit mass (kg) in J/kg. Measures how much energy a substance holds/released. High specific heat = a high amount of energy can be used.

State the chemical equation of photosynthesis of glucose

6H2O + 6CO2 → C6H12O6 + 6O2

Define half equations

Equations that shows redox (oxidation or reduction) of 1 element in the form of electrons and ions. If an electron is lost = oxidized, if an electron is gained = reduced

Explain how the principle of conservation of energy applies to calorimetry experiments

Since energy can not be created nor destroyed, the energy that the substances absorbs is the same as the energy the substance gained. In a calorimetry experiment, when one substance (like a hot metal) releases heat, that heat is absorbed by another substance (like water). The heat the substance loses (the hot metal) is equal to the heat the water gains, assuming no heat is lost to the surroundings.

What are the significance of three greenhouse gases in causing global warming and climate change?

Carbon dioxide- Most significant contributer of greenhouse gases, stays in the atmosphere for a long period of time, traps heat in the atmosphere and re-radiates toward Earth causing climate change. Emitted by fossil fuels and combustion

Methane- More potent than CO₂ with a higher global warming potential (GWP), immediate impact is more intense as it last in the atmosphere for a shorter amount time than carbon dioxide. Emitted from fossil fuels and agriculture (livestock) and landfills.

Nitrous oxide- Has a much more higher GWP than CO₂ and has a long lifetime. Emitted by agricultural activities (fertilziers, animal manure) or combustion of vehicles.

State the formula for sulfur trioxide (precursor/reactant of sulfurous acid)

2SO2 (g) + O2 → 2SO3

State the formula for sulfurous acid

H2O (l) + SO2 (g) → H2SO3 (aq)

State the formula for nitrous acid

2NO (g) + O2 (g) → 2NO2 (g)

State the formula for nitric acid

H2O (l) + 2NO2 (g) → HNO2 (aq) + HNO3 (aq)

Why do larger hydrocarbons have the tendency to undergo incomplete combustion?

They require more oxygen for complete combustion due to larger size and carbon content, making them more likely to burn incompletely.

How are fossil fuels formed?

Organic matter of ancient plants and animals sink to the bottom of land or ocean under layers of sediment. Over millions of years the weight of the overlaying layers and Earth’s internal heat causes the organic matter to decompose and transform into fossil fuels.

How is coal formed?

Formed from plant matter in swamps that decays under heat and pressure over millions of years, resulting in a carbon-rich rock.

How is oil and natural gas formed

Formed from marine microorganisms that are buried, then transformed by heat and pressure into oil and gas.

State the advantages/disadvantages of coal

Advantages- Cheap, plentiful throughout the world. Longest lifespan compared to other fossil fuels, can be converted into liquid fuel/gases, safer than nuclear power, ash produced can be used to make roads, high carbon content = high energy density
Disadvantages- Contributes to global warming due to carbon dioxide, contributes to acid rain (SO2), mining is dangerous, waste leads to chemical pollution

State the advantages/disadvantages of crude oil/petroleum

Advantages- Easily transported in pipelines/tankers, convenient fuel for cars because it is volatile (plentiful) and it burns easily, high enthalpy density
Disadvantages- Limited lifespan and uneven world distribution (social implications), contributes to acid rain and global warming, transport leads to pollution, smog is a secondary pollution that is released, carbon monoxide produced from incomplete combustion in gasoline of combustion engines

State the advantages/disadvantages of natural gas

Advantages- higher specific energy, clean (produces fewer pollutants per unit energy), easily transported in pipelines and pressurized containers, does not contribute to acid rain
Disadvantages- limited supplies, contributes to global warming, risk of explosion from leaks
How does carbon content relate to incomplete and complete combustion?

Why is carbon monoxide dangerous?

It is a poisonous gas that binds to haemoglobin which limits the ability of the blood to transport oxygen around the body.

State 3 reasons why crude oil is used as an energy source

High specific energy. It is easier to transport and handle due to its liquid form. Easy to vaporize for combustion.

State three reasons why gas is preferred to oil

It is more efficient as it produces more thermal energy per unit of mass/higher specific energy, produces less carbon dioxide per unit of output energy.

State the equations of methanol fuel cell

Anode-
Cathode-
Overall-

State the equations of hydrogen fuel cell
Anode-
Cathode-
Overall-

How does methanol fuel cell differ from hydrogen fuel cells?

Methanol is liquid and easier to store, but releases CO₂. Hydrogen fuel cells emit only water but require hydrogen storage and purification.

Why is high activation energy considered a useful property of fuel?

It prevents spontaneous ignition, making fuels safer to store and transport.

Which species are the oxidizing/reducing agents in a combustion reaction?

The fuel (hydrocarbon) is the reducing agent (loses electrons), and oxygen is the oxidizing agent (gains electrons).

What are the main differences between a fuel cell and a primary (voltaic) cell?

Fuel cells continuously require fuel and oxidant and run longer. Primary cells are limited by the amount of reactants and cannot be recharged.