Yr 12 sac 1
what is a fuel
a substance that can undergo a reaction to release energy (typically oxidation/combustion)
what is renewable
substance that can be replenished at the same rate at which is it consumed
fossil fuels origins
carbon based
biomass trapped in anaerobic enviro for millions of years (microorganisms)
Brown coal
less efficient that black coal (more water in it)
closer to surface
12MjKg-1
black coal
made at a higher temp/pressure than brown
thus more energy dense
17-24MjKg-1
Fossil fuel power stations process
chem potential energy
then heat energy
then kinetic energy in steam then turbine
electrical energy in dynamo
are fossil fuel power stations efficient/why
no, due to several transformations in energy efficiency is quite low
Natural Gas
formed in oilfields
mostly methane (CH4) due to plant life, thus simple
Petrol make up
roughly 8 (4-12) carbons in length (non-polar)
mostly alkanes, some alkenes and cyclic hydrocarbons
44-44MJKg-1
Diesel makeup
roughly 18 (12-24) carbons in chain
44-46MJKg-1
but less volatile
thus diesel engines more efficient than petrol
Biofuels
made of biomass
renewable
THEORETICALLY carbon neutral
less impact on Global warming
what is Biogas
up to 65% methan, also has CO2 (bad)
animal waste decomposing in anaerobioc enviro (cow farts)
Methane from biomass
refined from biogas (biomethane)
done through upgrading (removal of other gasses)
Hydrogen energy
142 MJKg-1 (much higher than petrol)
but hard to store/use, thus isnt used
Biodiesel
diesel alternatice as from triglycerides (plant/animal fat/oil)
it is diesel + carboxylic group
triglycerides
can be broken down into biodiesel through transesterification
this means adding heat, alcohol and catalyst
this breaks it up into three separate things with OCH3 on the end
what do triglycerides look like
refer to online or book now please
Bioethanol
common substitue for petrol in engines
produced from fermentatio of starch/sugars
12-18% ethanol produces
then distilled (separated by bp) to 99.8%
factors relevant in renewability
energy effficiency/out put
economic cost/benefit
environmental considerations
sustainability
energy efficiency equation
((energy obtained in desires form)/(energy available before conversion)) x100 (bc percent)
Negatives of biofuel
large volumes of water needed
inefficient energy source
requires large amount of arable land
What is Enthalpy
(H)
the total energy locked in a substance
can be measured as change in energy (triangleH)
Equation for Enthalpy
(triangleH)=(enthalpy of products)-(enthalpy of reactants)
What is the heat of combustion in enthalpy
change in enthalpy when substance burns in air (O2), which is always exothermic
If the value of change in enthalpy is negative
reaction is exothermic
if the value of change in enthalpy is positive
reaction is endothermic
when should KJg g-1 be used
when the substance is not pure, ie a mixture as it cannot be measured per mol
What is the general esterification equation
please look this up now
R-C(=O)-[O-H+H]-O-R -> R-C(=O)-O-R+H2O
carboxylic acid + alcohol -> ester + water
Define sustainability
we meet our required energy needs in the future without impacting our quality of life too much
How do u name an ester
alcohol + yl, carb. acid +oate (-oic acid)
What state are alcohols?
liquid not aq
What harmful gases do fossil fuels release
small amounts of so2 nox, biofuels release less
Why dont we have a hydrogen economy when the kj released by h is so higher than petrol and is clean
we cannot currently use it for most of our energy needs due to (Equipment has to be made, takes up a lot of space doesnt exist in large pure quantities)
what are the 2 types of fatty acids
saturated ( only c-c bonds) and unsaturated (c=c bonds)
how r triglycerides made
condensation reaction between glycerol and 3 fatty acids
How is glucose obtained
through the catalysed hydrolysis of glycogen and starch
What type of reaction is photosynthesis
redox endothermic
photosynthesis balanced eq
6co2(g) +6h2o= c6h12o6 + 6o2
anarobic respiration eq for animals
c6h12o6= 2ch3ch(oh)cooh (aq) lactic acid+ energy
anarobic fermentation eq for yeast
c6h12o6= 2c2h5oh (aq) ethanol+ 2co2 (g)
what is glucose stored as and how is it reconverted into glucose
glycogen, reconvert via hydrolysis
how do fatty acids give energy to the body
via oxidation
why are some amino acids essential
bc we dont make them ourselves and must come from diet
what is accuracy
how closely a measured experiment is to the true value
what is precision
the reproducability of a result (how close they are to each other)
what is repeatability
the ability for the same person, using the same instruments, method and setup to achieve consisten results
what is resolution
the smallest change in quantity that can be detected by the measuring instrument
What is uncertainty
half of the smallest scale of measuring on a given instrument
What is validity of measurement
the extent to which an experiment or measurement actually measures what it is intended to measure (does it directly address the aim/hypothesis)