what are the current and future options for supplying energy?

fuel

a substance with stored energy and can be released easily for heat or power

non-renewable fuel

fuel that cannot be replenished at the rate at which it is consumed

coal

non renewable fuel

• made from wood & plant material

• the longer left → the more energy

heavy pollutants

cheap

natural gases

non renewable fuel

• found in the earth’s crust

• formed with oil in muds that are low in oxygen & rich in organic matter

• extracted by driling → gas migrates to the surface for capture

• fracking process

high energy content & efficiency

leaks can cause explosions

petroleum/crude oil

non renewable fuel

• mixture of hydrocarbon molecules, mostly alkanes

• by itself has no fuel, needs to be seperated via distillation

high energy content

high carbon dioxide emissions

fossil fuels

non renewable fuel

• formed from the decomposition or buried dead organisms

renewable fuel

fuel that can be replenished at the rate at which it is consumed

biofuel

• fuel that is derived from plant materials (ie. grains, sugar cane, vegetable oil) and animal matter

• less impact on the enviroment

• plant materials used are produced via photosynthesis, removing CO₂ from the atmosphere

biodiesel

renewable fuel

• made from vegetable oil, animal fat or recycled resturant grease (triglyceride) and a small alcohol molecule (3x methanol)

  → produces 3x biodiesel + glycerol

  → process of transesterification

reduced pollutant

production requires land → deforestation

transesterification

• exchanging organic functional group of an ester with the organic group of an alcohol

biogas

renewable fuel

• fuel that is produced when organic matter (animal/food waste) is broken down in the absence of oxygen (anaerobic) / (fermentation of organic matter)

can be made from organic waste from farms

lower energy content & insufficient

anaerobic

the absence of oxygen

bioethanol

renewable fuel

• ethanol produced from plants (ie. starches and sugars) through catalysed fermentation, then distillation

  → seperate water

cheap and easy to produce

lower energy content

requires land to grow crops → deforestation

photosynthesis

6CO_2(g) + 6H₂O_(l) → C₆H₁₂O_6(aq) + 6O_2(g)

• endothermic

exothermic reactions

• if the total energy of the products is less than the total energy of the reactants, energy will be released from the system

  ie. CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂O_(l) + energy

respiration

• production of energy occuring in the mitochondria

• exothermic process - release of energy

• can be anaerobic or aerobic

cellular respiration

C₆H₁₂O_6(aq) + 6O_2(g) → 6CO_2(g) + 6H₂O_(l)

• aerobic

• exothermic

endothermic

• if the total energy of the products is greater than the total energy of the reactants, energy will be absorbed from the surroundings

  ie. CaCO_3(s) + heat → CaO_(s) + CO_2(g)

activation energy

• energy required to break bonds in reactants so that a chemical reaction can proceed

• all reactions require activation energy

secondary fuel

fuel that is produced from another energy source

fracking

process of pumping large amounts of fluid, mainly water, under high pressure into a drilled hole to break rock to release gas or oil

distillation

• process of separating the components of a liquid mixture through evaporation and condensation

strengths of renewable fuels

• sustainable & renewable

• carbon neutral

limitations of renewable fuels

• combustion of organic fuels is relatively inefficient

• deforestation for making biofuel

aerobic

prescence of oxygen

sustainable energy

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

hydrolysis

reaction when water is used to break chemical bonds

fats

• triglyceride

• broken down into glycerol & 3 fatty acids by hydrolysis

• oxidised in an exothermic reaction

fermentation

molecules are broken down anaerobically (anaerobic respiration)

anaerobic respiration

• called fermentation in plant & microorganisms

• occurs in tissues where there is a high demand for fast energy (ie. muscles), but shortage of oxygen to satisfy the energy needed

lactic acid

• by-product of anaerobic respiration

• can cause muscle soreness

fermentation of glucose/alcoholic fermentation

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (anaerobic respiration)

lactic acid fermentation

C₆H₁₂O_{6 (aq)} → 2CH₃CH(OH)COOH _(aq) (anaerobic respiration)

carbon neutral

carbon dioxide absorbed equals carbon dioxide released

specific heat capacity

energy needed to change the temp of 1g of a substance by 1°C

q=mc∆T

the spirit burner

• useful to compare fuels for energy

• inaccurate measures obtained due to heat loss to surroundings, underestimating the energy content

solution calorimetery

• any changes of enthalpy occurs directly in solution, usually water → more accurate ΔT measurements

• takes into account amount of heat absorbed by surroundings

• types of reactions used to burn fuels is limited

calibration factor

amount of energy required to change the contents of a calorimeter by 1 degree (J/°C)

• calibrating solution calorimeter involved measuring the amount of energy supplied & the corresponding temp change

• any changes of enthalpy occurs directly in solution, usually water → more accurate ΔT measurements

• takes into account amount of heat absorbed by surroundings

redox reactions

involved the transfer of electrons

reduction

gain electrons, reduce oxidation number

oxidation

lose electrons, increase oxidation number

oxidising agent/oxidant

allows for oxidation, itself reduces

reducing agent/reductant

allows for reduction, itself oxidises

basic solution (OH-)

KOHES (OH)

• add the same number of OH^- as to how many H^- added to both sides of the equation → neutralises H^- → becomes H₂O

KOHES

Key elements

Oxygen

Hydrogen

Electrons

States

heat loss & temp-time graphs

heat loss results to inaccurate ΔT values, and affecting ΔH values

• poorly insulated calorimeters will rise less in temp due to heat loss, and temp will fall after current is turned off

• welly insulated calorimeters will rise more in temp due to less heat loss, and temp will remain constant after current is turned off

viscosity

resistance to flow

• water = low

• honey = high

spontaneous reactions

reactions proceed on their own without the need for external supply of energy

internal circuit

movement of ions in solution

external circuit

movement of electrons (wire & electrodes)

electrodes

solids used to conduct electricity

electrolytes

liquids that can conduct electricity

purpose of the salt bridge

help maintains neutrality of solutions/charges

types of half cells

• metal ion-metal half cell

• solution half cell

• gas-non metal ion half cell

strengths of the electrochemical series

• determines relative strength of oxidising/reducing agents

• prediction whether a redox reaction will occur

• prediction of potential difference of the cell

limitations to electrochemical series

• does not tell us rate of reaction

• E⁰ only predicts reactions at SLC

fuel cells

type of galvanic cell

• requires constant supply of reactants

• oxygen always at the cathode

how fuel cells differ from primary galvanic cells

• fuel & oxygen supplied externally

• unreacted fuel & products are removed from the cell

• fuel cells don’t go flat, electricity generated for as long as reactants supplied (electrolyte does not run out)

• fuel cells are more efficient as there’s less energy transformations

primary galvanic cell

• convert chemical energy into electrical energy

• stored supply of reactants

• single use

• non rechargable

• 2 half cells

strengths of fuel cells

• keep maintaining electricity (no recharging required)

• less noise pollution

• products more environmentally friendly (hydrogen from biomass)

• convert chemical energy directly to electrical energy (more efficient)

limitations to fuel cells

• have to keep producing reactants

• more expensive

• hydrogen fuel cells mostly source hydrogen from fossil fuels

generating principles of fuel cells

• electrodes

  • porous

    → helps reactants diffuse through them

    → higher surface area means faster reaction

    → allow reactants to react with electrolyte

  • sometimes catalysts are embedded to help reaction speed up & take place at lower temperatures

  • reactant (fuel) + O₂ →

  • O₂ is mostly the oxidising agent

• operating temperature

  • higher temp → lower proportion chemical energy converted to thermal energy → more usable electrical energy (greater efficiency)

• electrolytes

  • type of electrolyte have impact on voltage output

  • name of fuel cell usually named after type of electrolyte

factors affecting efficiency of fuel cells

• electrodes

• temperature

• pressure

• humidity

• flow rate of reactant gases

challenges in production H_{2 (g)}

• hydrogen

• alcohol production

• using algae

problems with hydrogen

• storing hydrogen can be difficult (lightest element → must undergo compression)

• highly flammable & explosive → must be kept away from heat sources

• odorless, cannot be detected by humans

problems alcohol production

• maximising the conversion of organic matter to alcohol

• gas fermentation can use all biomass and available carbon, but low solubility of gases is a problem

problems using algae

• hard to harvest

how do fuel cells reduce energy waste

• using catalytic electrodes to ensure higher % of useful energy

• requiring fewer energy transformation

green hydrogen

• negative carbon emmissions

• from electrolysis, biomass, alcohol

hydrogen from electrolysis

• water decomposed into pure hydrogen & oxygen

• producing hydrogen gas from water (2H₂O_(l) → H_2(g) + O_2(g))

• expensive

hydrogen from alcohol

C₂H₅OH + H₂O → 2CO + 4H₂

CO + H₂O → CO₂ + H₂

• bioethanol used to produce H_{2 (g)}

• use of algae (as it rapidly absorbs CO₂, does not need much land & can be grown where land is unsuitable for food production)

hydrogen from biomass

C₆H₁₂O₆ + 2H₂O → 2CH₃COOH + 2CO₂ + 4H₂

• enzymes convert glucose

• crop residues & algae can be used

acidic solutions (H+)

KOHES

faraday’s first law

amount deposited, evolved or dissolved at the electrode is directly proportional to the quantity of electric current passed through the cell

faraday’s second law

to produce 1 mole of a substance, a whole number of moles of electrons (F) must be consumed