chap 2- developing fuels Flashcards
what is the volume of one mole of gas at room temp and pressure
24dm^3
what is room temp and pressure
298K and 100kPa
what is the formula for working out the number of moles in a volume of gas at RTP
no of moles = volume (dm3) / 24 or
volume in cm3 / 24,000
what is the ideal gas equation
PV = nRT pressure (Pa) volume (m3) R= 8.314 JK-1 mol -1 temperature (K)
how can you use a gas syringe to measure gas volume
attach gas syringe to opening of reaction vessel and it’ll show the total volume of gas produced in a reaction. Doesn’t show the difference between different gases
what types of reactions are bond making and bond breaking
bond making is exothermic as energy is released when bonds are formed
bond breaking is endothermic as you require an input of energy to break a bond
what is average bond enthalpy
the energy needed to break one mole of bonds in the gas phase, averaged over many different compounds
why does a double bond have a greater bond enthalpy than a single bond between the same elements
it is a shorter bond and electron density is greater as more electrons are shared but in a smaller area
what is standard enthalpy change of reaction
the enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions
what is standard enthalpy change of formation
the enthalpy change when one mole of a compound is formed from its elements in their standard states, under standard conditions
what is standard enthalpy change of combustion
the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
what is hess’ law
the total enthalpy change of a reaction is always the same regardless of the route taken
how do you find enthalpy change using a calorimeter
burn a flammable liquid (fuel) that will heat the water and if you know the mass, temp change and specific heat capacity of the water you can work out heat absorbed
how do you work out enthalpy change of neutralisation using a calorimeter
add a known volume of acid to an insulated container and measure the temp
add known vol of alkali and record temp rise while stirring
use Q=mc delta T to work out the heat needed to raise the temp of the solution formed
define a catalyst
a catalyst increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy. It is chemically unchanged at the end of the reaction
define catalysis
speeding up a chemical reaction by using a catalyst
what is a heterogeneous catalys
a catalyst thats in a different physical state to the reactants
how does a reaction happen on a solid heterogeneous catalyst
reactant molecules arrive at the surface and bond with the solid catalyst (adsorption)
the bonds between the reactants atoms are weakened and break up this forms radicals. the radicals get together and make up new molecules
the new molecules detatch from the catalyst
what are radicals
atoms or molecules with unpaired electrons
what happens if a catalyst is poisoned
they no longer work. the poison clings to the catalysts surface more strongly than the reactant does. so the catalyst can’t get involved in the reaction
what are cycloalkanes
saturated hydrocarbons with a ring of carbon atoms. general formula CnH2n
what is benzene
(C6H6) a cyclic alkene with 6 carbons and 3 double bonds. the double bond electrons are delocalised around the carbon ring
what is the difference between aliphatic compounds and aromatic compounds
aromatic compounds are also called arenes and have a benzene ring structure
aliphatic compounds are all other organic compounds eg alkanes and alkenes
what is the general formula for alcohols
CnH2n+1OH
what is a sigma bond
formed when 2 orbitals overlap in a straight line giving the highest possible electron density between the 2 positive nuclei so sigma bonds are usually very strong
what is a pi bond
formed when 2 p orbitals overlap sideways. weaker than a sigma bond
what is a double bond always made up of
a sigma bond and a pi bond
what is a stereoisomer
have the same shortened structural formula but a different arrangement in space
what is an electrophile
electron pair acceptors. attracted to places where there are lots of electrons
why does electrophilic addition happen
because the double bond has got plenty of electrons and so can be attacked by electrophiles
how is ethanol made
by hydrating ethene with steam at 300c and 60atm in the presence of phosphoric (v) catalyst
when are oxides of nitrogen produced
when the high pressure and temperature in a car engine cause the nitrogen and oxygen in the air to react together
what happens to unburnt fuel molecules from an engine
they come out as unburnt hydrocarbons
how is ground level ozone produced
when unburnt hydrocarbons and oxides of nitrogen react in the presence of sunlight
what is photochemical smog
made up partly by ground level ozone. it can irritate eyes, aggravate respiratory problems and cause lung damage
what are particulates
tiny particles of liquid suspended in the air
can settle in the lungs and cause decreased lung function and airway irritation also contribute to cardiovascular problems
