Developing fuels Flashcards
What is the equation for moles in a gas at room temp?
Moles = volume (dm3) / 24
What is the equation for moles in a gas not at room temp?
Pv = nRT
P = pressure (Pa)
v = volume (m3)
n = moles
R = gas constant (8.314 J K-1 mol-1)
T = temperature (K)
What are the conversions to get the units in the ideal as equation?
Pressure
KPa to Pa x1000
Volume
cm3 to m3 / 1x10-6
dm3 to m3 / 1x10-3
Temperature
+273
What is enthaply change?
(delta H)
the heat energy transfered in a reaction at constant pressure the units are KJ mol -1
What is the symbol for standard conditions and what are they?
25 degreese C
100 KPa
Is enthaply change for exo and endo thermic reaction + or -?
Exothermic -
Endothermic +
Is bond making/ breaking endo or exo?
Bond making = exothermic
Bond breaking = endothermic
What is the equation for average bond enthalpy?
Total energy absorbed to break bonds - total energy released in making bonds
What are the average bond enthalpies in the data book and why aren’t they accurate?
The energy needed to break one mole of bonds in the gas phase, averaged over many different compounds
A single bond e.g O-H is measure in many differernt compounds like water, carboxylic acids etc and they will all be different for differernt molecules even though its the same bond
What is bond length?
The distance between the two nuclei in a covalent bond where the attractive and repulsive forces balance out
How does both length affect bond enthalpy?
The stronger the attraction between the atoms, the higher the bond enthalpy and the shorter the bond length
Define the standard enthalpy change of reaction/ formation/ combustion/ neutralisation
Reaction = the enthalpy change when a reaction occurs in the molar quantities show in the equation under standard conditions
Formation = the enthalpy change when one mole of a compound it made from its elements under standard conditions
Combustion = the enthalpy change when one mole of a substance is completley burned in oxygen under standard conditions
Neutralisation = the enthalpy change when an acid and an alkali react to form one mole of water
What is Hesses law?
The total nehtalpy change of a reaction is always the same no matter the route taken
How do you draw a Hess cycle for enthalpy of formation numbers?
The equation on the top with the reactants going to the products
Elements in their normal states at the bottom
Arrows drawn from the bottom up
Elements formation numbers are always 0 (elements aren’t made)
How do you draw a Hess cycle for enthalpy of combustion numbers?
The equation on the top with the reactants going to the products
Combustion products on the bottom (CO2 and H2O balanced)
Arrows drawn from the top down
How do you draw a Hess cycle for enthalpy of reaction numbers?
The equation on the top with the reactants going to the products
ATOMs on the bottom e.g 2H and 2Cl not H2 and Cl2
Numbers will be average bond enthapies
Arrows drawn from top down
Work out like normal
Draw an energy level diagram for an exo and endothermic reaction
The less enthalpy a substance has the ____ stable it is
more
What is an intermediate?
They are formed halfway through a reaction
Usally very unstable
What is calorimetry?
It finds out how much heat is given out by a reaction by measuring the temperature change of water
How do you do an experiment using calorimetry to find the enthalpy change of combustion of a flammable liquid?
1) Burn the liquid as fuel
2) As the fuel burns it heats the water. You can work out the heat absorbed by the water if you know the mass of water, the temp change and the specific heat capacity of water (4.18)
How do you do an experiment using calorimetry to find the enthalpy change of reaction in a solution (neutralisation)
1) Add a known volume of acid to an insulated container and measure the temp
2) Add a known volume of alkali and measure the temp change
3) You can work out the heat given out by the reaction using q = mc∆T
What is the equation for enthalpy change in solution?
q = mc∆T
q = heat lost or gained (J)
m = mass of water (g)
c = specific heat capacity of water (4.18)
∆T = change in temp
What is a catalyst?
Increases the rate of reaction by providing an alternate
reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction
What is catalysis?
Speeding up a chemical reaction by using a catalyst
What are hetero/ homogeneous catalysts?
Heterogeneous = catalysts are in differernt states from their reactants
Homogeneous = catalysts are in the same states as their reactants
How do solid heterogeneous catalysts work?
Reactant molecules arrive at the surface and bond with the solid catalyst (adsorption)
The bonds between the reactants atoms are weakend and break up. This forms radicals and they get together and make new molecules. These detach from the catalyst (desorption)
Why are benzene rings stable?
The double bond electrons are delocalised around the carbon ring
Describe what a sigam bond is and how its made?
Single bonds
Is formed when two orbitals overlap in a straight line in the space between two atoms
This gives the highest possible electron density between the two positive nuclei so they are very strong covalent bonds
What is a pi bond?
A double bond is made of a sigma and pi bond
A pie bond is formed when two p orbitals overlap sideways
Pi bonds are weaker than sigma bonds
What is…
general formula
molecular formula
shortened structurual fomual
structrual formula
skeletal formula
?
general formula - describes any member of a family of compounds e.g Cn H2n+1OH for all alchohols
molecular formula - actual number of atoms of each elements in a molecule e.g C4H10
shortened structurual fomual - shows the atoms carbon by carbon with the attached hydrogens and functional groups e.g CH3CH2CH2OH
structrual formula - shows the atoms arranged in space and the bonds between them
skeletal formula - ^^^OH
What is structural isomerism?
The atoms are connected in different ways but have the same molecular formula
What is E/Z isomerism?
Restricted rotation around the C=C
A type of stereoisomerism
E (trans) isomer - when the groups are opposite sides to each other
Z (cis) isomer - when the groups are on the same side as each other (zusammen)
If the two groups are single H atoms use E/Z
If they are not e.g CH3 or Br use cis/trans
Describe addition polymerisation
(conditions and reagents too)
The double bond in an alkene opens up and joins monomers to make polymers
Conditions - nickel catalyst at high temp and pressure or a platinum catalyst at room temp and pressure
Reagent - hydrogen
How do you test for C=C bonds?
Shake with organe bromine water and it will turn colourless
Bromine is being added across the double bond to from a dibromoalkane
Describe electrophillic addition
The double bond opens up in a alkene and atoms are added to the carbon atoms
It happens because the double bond has lots of electrons and is easilly attacked by electrophiles
What is an electrophile?
Electron pairs acceptors e.g H+ or NO2+
Draw and describe the mechanism between ethene and bromine
Electrophillic addition
1) The double bond repels the electrons in Br2 polarising it
2) Heterolytic fission of Br2 - the closer Br gives up its bonding electrons and sticks to the C atom
3) A positivley charged carbocation is formed as an intermediate
4) The Br- bonds to it forming dibromoethane
How can you make alchohols
Reacting alkenes with water and H2SO4 catalyst
Alchohols are produced by hydrating alkenes in the presence of acid catalyst
What do you get when you burn an alkane completley
CO2 and steam (H2O)
Releasing huge amounts of energy (exothermic)
What is the green house effect?
The earth natrually radiates infrared radiation
Green house gasses (water vapour, CO2 and methane) in the atmosphere absorb some of it keeping the earth warm
What is produced in incomplete combustion?
CO
What is the effect of CO on human health?
They are chemically similar to O2 so bind to haemoglobin sites in RBCso less oxygen can be carried around the body
What are some pollutants from burning fuels and what are their side effects?
Unburnt hydrocarbons and oxides of nitrogen (produced when the high pressure and temperature in the car cause N2 and O2 in the air to react) contribute to smog
Hydrocarbons and nitrogen oxides react in sunlight to form ozone causing photochemical smog which can cause respiratory problems
Sulfur dioxide leads to acid rain caused by burning fossil fuels that contain sulfur which forms sulfur dioxide (gas) which dissolves in the moisture in the air making sulfuric acid
Particulates cause health issues (respiratory/ cardiovascular/ eye irritation)
How is pollution from burning fossil fuels being treated?
Sulfure dioxide from industial exhausts is removed using calcium oxide
Patriculates are removed using wet scrubbers and from car exhausts using filters
Catalytic converters - reduced CO, unburnt hydrocarbons, sulfur dioxide and nitrogen oxide from vehicles
What are some examples of renewable fuels?
wind, solar, wave, biofuels
What are biofuels?
Fuels made from living matter
bioethanol - ethanol is made by fermentation of sugar from crops
biodiesel - made by refining renewable fats and oils
biogas - breakdown of organic waste matter
What are the advantages and disadvantages of biofuels?
A
carbon neutral
Made from waste that would go to landfill
D
Car engines have to be modified to use
Lots of land needed to crop crops which won’t even be used for food
What are the advantages and disadvantages of hydrogen fuel?
Hydrogen gas can be burned or used in a fuel cell (converts H2 and O2 into water producing electricity)
A
Water is the only waste product
Hydrogen is abundant - can be extracted from sea water
Carbon neutral (depending on how the hydrogen is gained)
D
Requires energy to extract hydrogen from sea water
Difficult to transport and store
Highly flammable and has to be liquified which requires more builidngs and energy
