developing fuel Flashcards
ideal gas equation
pressure x volume = moles x ideal gas constant x temperature
units for ideal gas equation
pressure - pascals
volume - meters cubed
temperature - kelvin
conversion to pascals
atm x 1.01 x10^5 = Pa
kPa x10^3 = Pa
conversion to meters cubed
cm^3 x10^-6 = m^3
dm^3 x10^-3 = m^3
conversion to Kelvin
C + 273 = K
type of bonds in a single C-C bond
a sigma bond
electrons are arranged in an area of increased electron density between the carbon atoms
the orbitals for the two bonding electrons overlap in a straight line
type of bonds in a C=C double bond
a pi and a sigma bond
pi bond has two areas of negative charge and high electron density, above and below the σ bond
pi bond is weaker than a sigma bond
enthalpy meaning
The energy change from start to finish in a chemical reaction is its enthalpy
exothermic reaction meaning
energy released from system to the surroundings, increase in surroundings temperature, negative enthalpy
endothermic reaction meaning
energy absorbed from surroundings to system, decrease in surroundings temperature, positive value
standard conditions
1 atm pressure
298 K temperature
1.0 moldm-3 concentrations
units of enthalpy
kJmol-1
change in enthalpy symbol
delta H
enthalpy change of reaction
delta r H
the enthalpy change that accompanies a reaction under standard conditions
enthalpy change of combustion
delta c H
the enthalpy change when one mole of a substance is burnt completely in excess oxygen under standard conditions (in standard states)
enthalpy change of formation
delta f H
the enthalpy change when one mole of a compound in its standard state is formed from its constituent elements in their standard states under standard conditions
enthalpy change of neutralisation
delta neut H
the enthalpy change when one mole of H+ ions reacts with one mole of OH- ions to form one mole of water under standard conditions
calculating enthalpy change of combustion through experiment
method : calorimetry
1. measure 100 cm3 water into metal calorimeter
2. measure initial temperature of water
3. weigh + record initial mass of spirit burner
4. set up apparatus as shown, heat water, while stirring, until temperature stops changing
5. extinguish fuel by placing lid and reweigh spirit burner
6. record max temperature of water
calculating enthalpy change of combustion experiment calculations
a. q = m c deltaT
q (J) = mass of water x s.h.c x change in temp
b. n(fuel) = mass / Mr
c. enthalpy change of combustion = -q (kJ) / mol fuel
units = kJmol-1
enthalpy profile of exothermic reaction
reactants above products
enthalpy profile of endothermic reaction
products above reactants
bond enthalpy definition
the energy required to break one mole of the stated bond in a gaseous state, under standard conditions
bond enthalpy equation
bond enthalpy = bonds broken - bonds made
bond breaking is
endothermic
bond making is
exothermic
% error calculation
% error = ( (theory - experiment) / theory) x 100
finding precision of apparatus
half the smallest division of apparatus (unless digital, then don’t halve)
if a difference in two readings, double the precision error
finding the % uncertainty
(precision / reading) x 100
hess cycle to find enthalpy change of formation
use enthalpy change of combustion
enthalpy change of formation = + enthalpy combustion of reactants - enthalpy combustion of products
hess cycle to find enthalpy change of reaction
use enthalpy change of formation
enthalpy change of reaction = - enthalpy change of reactants + enthalpy change of products
catalyst purpose
- increase rate of reaction but are chemically unchanged at the end of the reaction
- provide an alternative pathway of lower activation energy
homogeneous catalysis
reactants and catalyst in the same state
heterogeneous catalysis
reactants and catalyst in different state
mechanism of heterogeneous catalysis
- reactants diffuse towards catalyst surface
- reactants adsorb onto catalyst surface (weakens bonds and lowers activation energy)
- weaker bonds in the molecule break
- new bonds in molecules form (new products form on catalyst surface)
- products desorb from the catalyst surface
catalyst poison definition
A substance that stops a catalyst from properly functioning
cracking definition
the process of making one larger organic molecule into two or more smaller ones
cracking conditions
very high temperatures and pressures
catalytic cracking
alkane is heated and the vapour is passed over a hot zeolite catalyst
makes more branched products, better fuel
thermal cracking
alkane vapour is mixed with steam and heated to a very high temperature
makes more short alkenes, makes straight chain fuels
what are particulates
small particles of solids or liquids produced by volcanoes or burning fuel. can cause damage to animals and humans
cause of photochemical smog
unburnt hydrocarbons from car engines
what is CO + its dangers
carbon monoxide
from incomplete combustion
toxic gas
can cause photochemical smog
dangers of CO2
contributes to the greenhouse effect
dangers of nitrous oxides
produced through combustion of fuels in air
creates photochemical smog and acid rain
dangers of sulfur oxides
produced by volcanoes and burning of fuels with sulfur impurities
lead to acid rain and are toxic
dangers of acid rain
corrodes limestone and causes damage to life
dangers of photochemical smog
reduces visibility and causes respiration problems
methods of removing pollutants
- catalytic converter
- Sulfur oxides can be removed by reacting them with calcium oxide
catalytic converter process
converts pollutants to safer molecules
saturated hydrocarbon meaning
contains only single C-C bonds
unsaturated hydrocarbon meaning
contains double C=C bond(s)
benzene features
- a hydrocarbon (C6H6)
- in a closed ring shape
- ## It has three double bonds, but the p electrons are delocalised around the whole ring so it reacts slightly differently to other hydrocarbons with double bonds
aromatic definition
A compound containing at least one ring of a planar flat molecule with delocalisation (such as benzene)
aliphatic definition
compound with no rings
homologous series definition
a group of compounds with the same general formulae but different molecular formulae
general formula for alcohols
Cn H2n+1 OH
general formula for alkanes
Cn H2n+2
general formula for alkenes
Cn H2n
general formula for cycloalkanes
Cn H2n
complete combustion of a hydrocarbon
hydrocarbon + oxygen -> carbon dioxide + water
incomplete combustion of a hydrocarbon
hydrocarbon + O2 -> H2O + CO + C
polymers definition
long molecules made from smaller monomers
copolymers definition
polymers consisting of multiple types of monomers
addition polymers conditions
high pressure and catalyst
addition reaction meaning
two or more molecules join, breaking a double bond to form a single product
electrophile definition
electron pair acceptor (to form covalent bonds)
has partial positive charge
testing for unsaturation
Add a few drops of low concentration bromine water to the sample and shake
if solution unsaturated, solution will turn colourless
structural isomer definition
the same molecular formula as another isomer but a different structural formula (so it has the same number of atoms, but in a different arrangement)
E/Z isomerism criteria
- C=C or ring (prevents rotation)
- two different groups on each C in the C=C bond
E isomer
opposite
hydrogen atoms are on opposite sides of double bond
aka trans isomers
Z isomer
same
hydrogen atoms are on the same side of double bond
aka cis isomers
features of biofuel
- produced from plant / animal materials
- burning them still releases CO2
- if the plants/trees used to produce them are replanted, the new ones ‘reabsorb’ this CO2 with photosynthesis
features of hydrogen as a potential fuel
- created through electrolysis of water
- combustion only produces only water
- less energy dense than petrol
- nitrous oxides still produced at high temperatures
