CHEMISTRY EVERYTHING

Fuel

a substance with stored energy that can be released relatively easily for use as heat or power.

Why are H+ ions required in oxidation reactions?

Oxidation reactions using oxidising agents like MnO₄⁻ require H⁺ ions to provide hydrogen for water formation and balance oxygen atoms during reduction.

The acidic environment also increases the oxidising strength of MnO₄⁻, allowing it to be fully reduced to Mn²⁺ rather than MnO₂.

Renewable Fuels

Recourses that can be replaced by natural processes within a relatively short period of time

Examples of Renewable Fuels

Bioethanol, Biogas, Biodiesel.

Examples of Non-Renewable Fuels

Coal, Crude Oil, Natural Gas.

Fossil Fuels

Combustible blackish sedimentary rock, consisting primarily of carbon, found underneath the Earth, formed from dead plant matter that has been subjected to high temp and high pressure over millions of years.

Natural Gas

Composed of ~80% methane, ~20% other hydrocarbons, used for heating and electricity.

Fracking

the process of obtaining natural gas that is found with coal or shale deposits.

Coal Seam Gas (CSG)

Natural gas obtained from reserves found under the earth, specifically from coal or shale deposits.

Crude Oil (petroleum)

Mixture of hydrocarbons (alkanes, cycloalkanes); refined to petrol and diesel.

sustainable

the ability to meet present needs without compromising the ability of future generations to meet their own needs

Carbon Neutral

refers to the recycling of carbon, the carbon released as a greenhouse gas (CO₂) is approximately the same amount absorbed during the process of fuel creation.

Enhanced greenhouse effect

a consequence of increased greenhouse gas concentrations in the atmosphere due to human activities.

Biofuels

A renewable fuel source derived from biological matter.

Bioethanol

Produced when glucose from plant matter is fermented.

Production of bioethanol

1. fermentation of glucose

   • glucose is obtained from plants (sugarcane, wheat)

   • enzymes catalyse the fermentation process to produce ethanol

2. distillation

   • fermentation produces a solution that is 10%v/v ethanol (ethanol needs to be separated from water to produce a useful fuel)

   • solution is heated so ethanol gas (BP~78ºC) is collected top of the column while water stays at the bottom

   • ethanol collected and dehydrating agents are used to remove remaining traces of water

     REQUIRES SIGNIFICANT QUANTITY OF ENERGY TO BOIL → not carbon neutral

%v/v

refers to how much of a particular liquid is dissolved in a 100 mL solution.

Biogas

Combustible, renewable fuel produced when animal waste or other organic material rots in the absence of oxygen.

• consisting mainly of CH4 and CO2

Biodiesel

Derived from triglycerides in vegetable oils or animal fats via transesterification.

Viscosity

The measure of a fluid’s resistance to flow

Photosynthesis

The chemical process undertaken by plants to convert light energy into chemical energy.

• endothermic

Cellular Respiration

The process of using glucose produced by plants to produce energy in the cells of organisms.

Glucose

One of the main fuels that is used to power the organisms, classified as a monosaccharide.

Enthalpy (H)

The total chemical energy contained in a substance.

Change in enthalpy (∆H) + why does it occur?

The measurement of the difference in enthalpy between products and reactants, indicating energy absorbed or released during a chemical reaction.

• occurs because bond breaking absorbs energy and bond formation releases energy, resulting in an overall enthalpy change.

Activation energy

The minimum amount of energy required for a reaction to occur

Exothermic reaction

• net release of energy to the surroundings

• enthalpy of the products is smaller than that of the reactants.

Endothermic reaction

• net absorption of energy into the system

• enthalpy of the products is greater than that of the reactants.

Thermochemical equations

Chemical equations that display both the chemical reaction and the change in enthalpy.

Heat of combustion

The heat released when 1 mole of fuel undergoes complete combustion, measured in kJ/mol or kJ/g.

Incomplete combustion

Occurs when the supply of oxygen is limited, producing water, carbon monoxide, and/or carbon.

Bond enthalpy

The average value of enthalpy per mole required to break a given bond in the gas phase, indicating the difficulty of breaking a bond.

Oxidisation

The loss of electrons, also defined as the gain of oxygen according to IUPAC.

Standard conditions (SLC)

• 1M

• 298 K (25ºC)

• 100 kPa

Calorimetry

An experimental technique used to determine the heat of combustion by measuring temperature changes.

Chemical reaction

A process that involves the transformation of reactants into products, accompanied by energy changes.

Calibration Factor (CF) + purpose

The energy required to increase the temperature of a set quantity of water within a calorimeter by 1ºC.

• energy is needed to heat the water and the internal components of the calorimeter

• Without calibration, the enthalpy value obtained will always be less than the true value for a given calorimeter using a fixed quantity of solution.

What are the limitations of HPLC?

• no info on the functional groups of any compounds

• retention time is not unique (some compounds have very similar retention times)

• dependence on reference standards - without a calibration curve, it is difficult to assign peaks

Dissolution

The process where a solute in a gaseous, liquid, or solid phase dissolves in a solvent to form a solution.

Ways to decrease energy loss in calorimetry

• Placing a lid on the beaker

• insulating the beaker

• ensuring sufficient oxygen is present

Solution Calorimeter

A calorimeter where the reaction takes place in solution.

Limiting Reagent

The chemical that is fully consumed in a chemical reaction and limits the amount of product that can be made.

Excess Reagent

The chemical that remains after the limiting reagent has been fully consumed, determining the quantity of products.

What is the relationship between temperature and volume?

Temperature is proportional to volume. T*V = constant
e.g. double the temperature means volume also doubles

Reduction

The gain of electrons, gain of hydrogen, or loss of oxygen.

Conjugate Redox Pair

Two chemical species where one is the product of either oxidation or reduction from the first chemical.

Galvanic Cell

A type of electrochemical cell in which chemical energy is converted into electrical energy.

Fuel Cell

A type of galvanic cell that continuously generates electricity through a spontaneous redox reaction

Electrode

The site of oxidation and reduction in an electrochemical cell.

Salt Bridge

A component that allows for the movement of ions and prevents charge build-up in half-cells.

Inert Ions

Ions that do not participate in redox reactions and do not form precipitates with common ions in solution.

Spontaneous reaction

Occurs when an oxidising agent reacts with a reducing agent, with the oxidising agent sitting higher than the reducing agent on the electrochemical series.

Standard hydrogen electrode

The half-cell against which Eº values are determined, with an Eº value arbitrarily assigned as zero.

Principles + design features of galvanic cells

• Two half-cells – each contains an electrode in contact with an electrolyte solution of its own ions.

• Electrodes –

  • Metals often act as electrodes (e.g., Zn, Cu).

  • If no solid conducting metal is present (e.g., for gases or ions only), an inert electrode like platinum or graphite is used.

• Salt bridge (or porous separator) – completes the circuit by allowing ion migration to maintain electrical neutrality, without direct mixing of solutions.

• External circuit – a wire connecting the electrodes, allowing electron flow from the anode (oxidation site) to the cathode (reduction site).

• Direction of electron flow – always from the anode (negative electrode) to the cathode (positive electrode).

Porous electrodes

Have larger surface area to increase cell efficiency and rate of chemical reaction, allowing gaseous reactants to spread more evenly.

Biofuels VS Fossil fuels

• Biofuels are often described as carbon neutral because the carbon dioxide released during combustion almost neutralises the carbon dioxide absorbed by plants during photosynthesis.

• however extra CO2 is emitted during cultivation, processing and transport

• Fossil fuels result in a net increase in the CO2 being released into the atmosphere

Advantages and disadvantages of fuel cells

advantages:

• More efficient than combustion engines due to direct conversion of chemical energy into electrical energy.

• quieter

• bioethanol is closer to carbon neutral than fossil fuels (assuming question asks for ethanol fuel cell vs combustion engine powered by fossil fuel)

• produce less greenhouse gases

disadvantages:

• safety concerns associated with storage and transport of fuels

• High production costs (expensive catalysts, hydrogen via electrolysis using renewables)

• Most hydrogen today comes from fossil fuels (steam reforming of natural gas) → not fully “green”.

• Infrastructure limitations makes large-scale adoption difficult.

Production of Hydrogen Gas

• steam reforming

• electrolysis of water: is a process that uses electricity to split water into hydrogen and oxygen gas. → NO CO2 PRODUCED

uses and limitations of electrochemical series

USES

• identifies which species is more likely to be oxidised or reduced

• used to deduce overall equations

• determine maximum cell voltage under SLC

LIMITATIONS

• Only accurate at SLC and when 1 M concentration solutions.

• no information about rate of reaction is provided.

• no info on extent of reaction

common design features of a fuel cell

• Two electrodes

  • Anode: site of fuel oxidation

  • Cathode: site of oxidant reduction

  • Often porous and coated with a catalyst (like Pt) to increase ROR

• Electrolyte / ion-exchange membrane

  • Allows only certain ions (e.g., H⁺ in PEM fuel cells, OH⁻ in alkaline fuel cells) to pass between electrodes.

  • Prevents fuel and oxidant mixing directly.

• Porous electrodes

  • Provide large surface area and good diffusion for gaseous reactants.

• Continuous reactant supply

• External circuit

• Separator / membrane layer

  • Keeps fuel and oxidant apart but allows ionic conduction, maintaining charge balance.

Open System

A system in which matter and energy can be exchanged with the surroundings.

Closed System

A system in which only energy is exchanged with the surroundings.

Collision Theory

1. there must be sufficient kinetic energy to overcome the activation energy barrier.

2. particles must collide with the correct orientation

example question: why don’t all reactions happen instantaneously?

Extent of Reaction

refers to how much of product that will be present, typically at equilibrium.

• aka, the ratio of products to reactants.

Rate of Reaction

the change in concentration of the product/reaction per unit time.

Surface Area Effect

Increasing the surface area increases the number of particles exposed and able to collide per unit time, resulting in more successful collisions.

Concentration Effect

Having a larger concentration results in many reactant molecules available for collisions.

Temperature Effect

If the temperature increases, the proportion of reactant molecules that have sufficient energy to react successfully increases.

It also increases the amount of kinetic energy between particles, thus increasing the frequency of collisions, hence rate of chemical reaction.

Catalysts

Catalysts reduce the activation energy by providing an alternative pathway for the reaction to occur.

• this allows a greater proportion of collisions to exceed the activation energy barrier, speeding up the rate of reaction.

• not consumed in a reaction

• allow reactions to be carried out at a lower temperature

Irreversible Reactions

Reactions where the products are not able to collide with themselves to reform the reactants, e.g., combustion reactions.

Reversible Reactions

Reactions where the products can collide with themselves to return to the reactants, e.g., redox reactions.

• indicated by double arrow

Dynamic Equilibrium

Occurs in a closed system at a fixed volume where the rate of the forward reaction equals the rate of the backward reaction.

Equilibrium Law

When a chemical reaction is at equilibrium, the ratio of the concentration of products to reactants will always be a specific value at a set temperature.

DO NOT include liquid water in equilibrium expression when other reactants are aqueous solutions

Le Chatelier's Principle

States that the system will shift equilibrium to partially oppose any change made.

High Temperature Effect

Increases the reaction rate but may reduce yield of products in exothermic reactions.

Low Temperature Effect

Favorable for product yield in exothermic reactions but slows the rate of reaction significantly.

Principles and operating conditions of electrolytic cells

Electrolysis: non-spontaneous redox reaction driven by an external direct current power source.

• Electrons are forced into the cathode and drawn from the anode

• Products form at the electrodes and may need to be removed as they form to:

  • prevent spontaneous reverse reactions,

  • improve efficiency,

  • enable product collection (e.g., Cl₂ gas removal).

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Common design features

1. Power source

   • Supplies sufficient voltage to overcome the reaction’s non-spontaneity and cell resistance.

2. Electrodes

   • Must conduct electricity and be chemically suited to the reactions.

   • Inert electrodes (e.g., graphite, platinum) when electrode material should not react.

   • Active electrodes (e.g., Cu in copper refining) when electrode itself participates in the reaction.

3. Electrolyte

   • Must provide mobile ions to carry charge.

   • May be molten (e.g., molten NaCl) or aqueous solution (e.g., NaCl(aq)).

   • Choice of state affects products (water may compete as a reactant in aqueous solutions).

4. Membranes

   • Physical barriers (e.g., diaphragms, membranes) can prevent products from mixing.

   • To facilitate the flow of ions to the cathode to complete the circuit

Anhydrous

A term describing a substance that contains no water.

Applied voltage

The voltage that must exceed the predicted value from the electrochemical series for a reaction to occur.

Molten electrolytes

Electrolytes in a liquid state used when water is a stronger oxidizing agent than the ions present.

Electroplating

The process of coating an object with a thin layer of metal to protect a more reactive layer or to retouch a worn surface.

Faraday's first law of electrolysis

States that the mass of a substance produced at an electrode is directly proportional to the total electric charge (Q) passed through the electrolyte.

Charge (Q)

Measured in coulombs (C), it represents the total electric charge passed through the electrolyte.

Faraday's second law of electrolysis

States that to produce 1 mole of a metal, a whole number of moles of electrons must be consumed.

Nature of Electrodes

Some materials have lower conductivity or reactivity. Inert electrodes (like Pt) don't participate in reactions but must still conduct electrons well.

Features and operating principles of a secondary cell

General operating principle

• Discharge (galvanic)

• Recharge (electrolytic)

Common design features

1. Electrodes

   • Must undergo reversible redox reactions (so products formed on discharge can be converted back on recharge).

   • Stable, durable, able to withstand repeated cycling.

2. Electrolyte

   • Allows for the movement of charged ions

   • Can be liquid, gel, or solid (but not ionic solid because ions cannot move freely)

1. External circuitry

   • Allows electrons to flow during discharge to a device.

   • During recharge, connects to a DC power supply that pushes current in the opposite direction.

Requirements to be able to recharge a secondary battery

• The discharge reaction must be reversible

• the products of the discharge reaction MUST remain in contact with the electrodes

• the products of the discharge reaction MUST NOT participate in side reactions

• a voltage greater than the discharge reaction must be applied during recharge

Pros & Cons & solutions of Hydrogen Fuel

Advantages:

• Hydrogen has a high energy density

• the only product of hydrogen combustion is water.

• less GHG emissions

Problems/disadvantages

• Process requires constant energy source, and renewable energy is not always used

• Highly flammable and leaks easily

• Hydrogen gas products take up a lot of space (not compressed) making it hard to store.

• Expensive

• green hydrogen via electrolysis requires a lot of energy

solution:

• Stored in containers that can maintain high pressure and very low temperatures.

• Produce hydrogen where it’s used (e.g. at refuelling stations) to avoid long-distance transport.

• use renewable energy or obtain hydrogen from artificial photosynthesis

PEM electrolysis

Polymer electrolyte membrane.

Concept: Uses a solid polymer electrolyte (proton-exchange membrane) that allows H⁺ ions to pass but blocks gases (O₂, H₂).

• Powered by renewable energy sources (like solar or wind energy)

• Innovation: compact design, fast response, high purity hydrogen.

• REQUIRES POROUS ELECTRODES

Advantages of innovation:

• High efficiency when powered by renewables.

• Modular, scalable, suitable for decentralised hydrogen production.

• Produces green hydrogen with no carbon footprint.

Disadvantages:

• Cost: Expensive catalysts (Pt, Ir) and membranes

• Energy input: Still needs significant electricity input.

Artificial photosynthesis

Concept: Mimics natural photosynthesis using catalysts to directly harvest sunlight for water splitting.

• Water oxidation catalyst at the anode generates O₂ and protons.

• Proton reduction catalyst at the cathode reduces H⁺ to H₂.

• uses photoelectrodes

Equations (acidic medium):

• Water oxidation (anode):
  2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e⁻

• Proton reduction (cathode):
  4H⁺(aq) + 4e⁻ → 2H₂(g)

• Overall:
  2H₂O(l) → 2H₂(g) + O₂(g)

Advantages of innovation:

• Directly couples sunlight to chemical fuel (no need for external solar cells).

• Potential for highly sustainable, low-cost hydrogen production.

• Could provide distributed hydrogen production using abundant inputs (sunlight + water).

Disadvantages:

• high development cost

• Catalysts and photo-absorbing materials often degrade quickly when exposed to sunlight, oxygen, and water.

• low efficiency (currently)

homologous series

A family of hydrocarbons where each successive molecule differs by a -CH2- unit

Saturated

all covalent bonds between carbon atoms are single bonds

structural isomers

same chemical formula, bonded in different arrangement

Cyclohexane

a saturated cyclic alkane with the formula C6H12

addition reaction

addition of a smaller molecule to make a single product

polymer

structure made up of repeating monomers

degree of unsaturations

Refers to how many hydrogen atoms a molecule contains compared to the maximum possible number for that number of carbon atoms.

• (C=C bonds)

benzene

has formula C6H6

phenyl group:

• A substituent group derived from benzene by removing one hydrogen atom.

• Formula C₆H₅–.

• must be attached to another group, cannot exist on its own

Why do tertiary alcohols not oxidise?

• The carbon bearing the –OH group is bonded to three other carbons, so it has no C–H bond available to break.

• oxidation requires removal of that hydrogen

Transesterification reaction

A chemical reaction between vegetable oils/animal fats and an alcohol using a catalyst.