chem Flashcards
what trend is there in atomic radius as we move left to right across a period? why?
decreases
increased nuclear charge which pulls electrons closer
what trend is there in 1st ionisation energy as we move left to right across period three? why?
increases
increased nuclear charge means more energy needed to remove electrons
what are the chemical formulae of phosphorus, sulphur and chlorine
P4
S8
CL2
as we move across period three why is the 1st ionisation energy of S lower than P despite an increase in nuclear charge
Sulphur has 2 of its 3p electron paired, while phosphorus does not. the paired electrons repel.
what type of structure does phosphorus, sulphur and chlorine have
molecular
which element in period two, lithium to neon would have the highest 2nd ionisation energy
lithium
because the electron is being removed from the 1s sub shell which is closer to the nucleus and experiences less shielding so is harder to remove an electron
why are 2nd ionisation energies greater than 1st ionisation energies?
takes more energy to remove an electron from a positive ion
as we move across period 3 why is the 1st ionisation energy of Al lower than Mg despite an increase in nuclear charge?
electron being removed from higher energy sub-shell. 3s in Mg and 3p in Al
what trend is there in melting and boiling point within period 3? why?
increases Na-Al as the charge of positive metal ions increases.
for the non metals strength of van der waals forced, governed by size of molecules mean S>P>Cl>Ar
Si has highest as its giant covalent
write an equation for the first ionisation energy of E
E(g) -> E+(g) + e-
what type of structure does silicone have
macromolecular
why does temp not increase while a substance is melting or boiling
the energy is absorbed as the bond weakens
what effects the strength of a permanent dipole-dipole force
the bigger the difference in electronegativity between a bonding pair the greater the diploe so the greater the force
starting with the weakest, name the 3 types of intermolecular attraction
van der waals
permanent dipole-dipole
hydrogen bonding
what can we say about the polarity of bonds between different elements
they will be polar to different extents depending on the elements
what are giant covalent bond held together by
covalent bonds
what can we say about the polarity of bonds in elements
they are not polar
what are molecular crystals held together by
intermolecular force hold molecules together covalent bonds hold the atoms within molecules together
what is a dative covalent bond
a shared pair of electrons, where both have been supplied by one atom
what is meant by a polar bond
where the charge is not symmetrical, so one area is more positive and one area is more negative
what causes permanent dipole-dipole forces
attraction between molecules with permanent dipoles
what causes a hydrogen bond
when hydrogen covalently bonds to N,O,F. the H can be shared with this or a lone pair of another electron
what are ionic crystals held together by
electrostatic attraction between oppositely charged particles
what are the four types of crystal structures
ionic, metallic giant covalent and covalent
where do we find van der waals and what effects its strength
found in all atoms and molecules. the more molecules the bigger the force
how do we convert cm3 to dm3
divide by 1000
if we make a change to conc. temp. or pressure how will the equilibrium respond
it will move to reduce the disturbance
why might a compromised temp be used
a high temp will decrease the % of product at equilibrium
a low temp will mean that equilibrium is reached to slowly to be economically viable
other than yield why might a compromise pressure be used
cheaper
why do haber process plants run at a higher temp and lower pressure that would produce the maximum conversion
high temp = faster
low pressure = less expensive
ammonia
NH3
what is 80% of ammonia used to make
fertilisers
define molecular mass
the average mass of a molecule compared to 1/12th the mass of an atom od C-12
what equation links moles, conc, and volume
n=cxv/1000
define relative atomic mass
the average mass of an atom compared to 1/12th of the mass of C-12
what effect does a catalyst have on the position of equilibrium
none
write an ionic equation to summarise NaOH+HCL -> NaCL=H2O
H+(aq) + OH-(aq) -> H2O (l)
what is the difference between dynamic equilibrium and equilibrium
equilibrium means hat the conc. of reactants and products are unchanged, addition of the word dynamic means the reaction is still preceding while the situation exists
what is methanol used for
motor fuel
starting material
what is ethanol made from ethane used for
making cosmetics, drugs, inks, detergent
give the chemical reaction for the hydration of ethane to form ethanol
C2h4 + h2o -> c2h5oh
what is the equation for calculating % yield
(actual yield/ theoretical) x100
how do you convert from empirical formula to molecular formula
work out mass of the empirical and molecular formula. divide empirical by molecular. multiply the number by each element in the empirical formula
what is an equilibrium mixture
the mixture of chemicals found in a dynamic equlibrium
what is the equation used to calculate % economy
molecular mass of desired product/sum of all molecular masses x100
what is empirical formula
the simplest ratio of atoms of each elements in a compound
what is a reversible reaction
a reaction which can proceed in either direction between reactants and products
in the context of heterogeneous and homogeneous what is a phase
different physical state
what are the two catalysts what do they mean
homogeneous- same phase
heterogeneous- different phase
how do catalyst work
they provide an alternative route for the reaction, with a lower activation energy
what effect do catalysts have on the position of equilibrium for reversible reactions
none
what is the meaning of the term catalyst
something that alters the rate of a chemical reaction, but is not used up in the reaction
what does increasing the conc. increase the rate of reaction
makes collisions more likely
why does temp have such a big impact on rate
temp increases the number of particles with energy above the activation energy
on a M-B distributions, where is the average energy in reletion to the most probable
right
do most collisions between particles result in a chemical reaction why
no
they may not have enough energy or the wrong orientation
five factors that effect rate reaction
temp conc pressure surface area catalyst
what is the catalyst in a catalytic converter in a honeycomb shape
to provide a much greater surface area
define activation energy
minimum amount of energy to start a reaction and break bonds
do any particles in a gas have 0 energy
no
what are zeolites
minerals with a very open pore structures that ions or molecules can fit into. they are used as catalysts
what does collision theory tell us
that reactions can only occur when collisions take place between particles that have enough energy
what effect to catalyst have on enthalpy change for reactions
none
what does the prefix ‘di’ mean
two of them
what does the production of greenhouse gases contribute towards
global warming
why do we crack hydrocarbons
to produce smaller molecules that are higher in demand
what is empirical formula
the simplest whole number ratio in which atoms in a compound combine together
what greenhouse gas, does burning fossil fuels release into the atomosphere
CO2
what does a negative sigh infront of delta H mean
forward reaction is exothermic
name a catalyst used in a catalytic converter
platinum or rhodium
give the equation for the reaction of carbon monoxide with hydrogen to form methanol
CO + 2H2 -> CH3OH
how do you convert concs. from gdm-3 to moldm-3
divide by molar mass
what is meant by agravados constant
number of partials in a mole.
how does fractional distillation work
crude oil is heated, it is hotter at the bottom and coolest at the top vapours pass up the tower through tray with bubbles caps. when they arrive at a tray that is sufficiently cool they condense into a liquid where they are piped off
what are the 1st six prefixes of organic molecules
meth eth prop but pent hex
where do we collect shorter chain hydrocarbons from in a fractionating tower
near the top
where we have more than one functional group, how do we decide which one to write first
functional groups go in alphabetical order
what does cracking do to the c-c bonds in alkanes
breaks them
what do we call a hydrocarbon with a =
alkene
when writing out names of molecules, where do we put a hyphen
between names and numbers
what problems might carbon produced by incomplete combustion have on health and the environment
asthma, damages lungs and global diming
what do we call the thick residue that collects at the bottom of the fractioning tower
tar/ bitumen
what is meant by displayed formula
a formula of a compound drawn out so that every carbon atom and every bond is shown
what homologous series is petroleum mainly made of
alkanes
what are the conditions and main products of thermal cracking
high temp
high pressure
high percentage of alkenes
what issues are there with burning a fuel that contains sulfur
sulphur dioxide will be produced that causes acid rain
what amount of energy do most particles have? how can we find this from a M-D distribution
an intermediate amount of energy at the peak of the curve
what are functional group isomers
where isomers have different functional groups
what are the 3 types of structural isomers
chain, position, functional group
what are positional isomers
where the functional group in isomers is attached to the main chain at different points
how is sulphur dioxide removed from flue gases
using CaO
this reacts with the SO2 to produce CaSO4 which is used as plaster
where must a reaction be in order for a dynamic equilibrium to be reached
a closed system
what can we say about the proportion of reactants and products at equilibrium
any ratio not 50;50
how do we remove the pollutants produced by the internal combustion engine
using a catalytic converter
when moving left to right across period 3, what exceptions are there for the trend in increasing 1st ionisation energy? why?
aluminium- electron removed by 3p
sulphur- two electrons in 3p so repulsion occurs
what are alkanes
saturated hydrocarbons
what two products are produced by the complete combustion of hydrocarbons
carbon dioxide and water
what is meant by molar volume
1 mole of any gas takes up 24000 of space at room temp and pressure
what is meant by homologous series
a set of organic compounds with the same functional group
what is meant by functional group
an atom or group of atoms in an organic molecule which is responsible for the characteristic reactions of that molecule
what is meant by structural formula
a way of writing out an organic formula in which bonds are not shown but each carbon atom is written separately with the atoms or groups attached to it.
what is structural isomerism
where molecules have the same molecular formula, but a different structural formula
what are the conditions and main products of catalytic cracking
slight pressure
high temp
zeolite catalyst
what are chain isomers
where the hydrocarbon chain in isomers is arranged differently
what products would we expect from the incomplete combustion of a hydrocarbon
carbon monoxide and water
what is le chateliers principle
if a system in equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance
in practice what conditions are used for producing methanol from carbon dioxide and hydrogen
500K
10,000kPa
what is the equation for the Haber process
N2 + 3H2 2NH3
what temp and pressure is used in most plants for the haber process
20,000kPa
670K
what do we call the process of reactants sticking to the surface of a catalyst
adsorption
which catalyst is used in the production of ethanol from ethene
phosphoric acid absorbed on silica
in practice, what conditions are used to produce ethanol from ethene
570K
6500kPa
what do we call the process of breaking away from the surface of a catalyst
desorption
what type of structure does argon have
atomic
what happens to the total area under a M-B distribution curve when the temp is changed
no change
what causes Van Der Waals forces
caused by instantaneous dipoles. these occur because in any instant electrons are not spread evenly and more will be in one another.
what do we call a hydrocarbon with a group 7 element attatched
halo- alkane
what can we say about a reaction in dynamic equilibrium
in a closed system, the rate of the forward and reverse reactions are the same so conc. is same
what are alkanes mainly used for
fuels
what happens to the boiling point of alkanes as chain length increases
increases
name 3 greenhouse gases
CO2
methane
water vapour
in terms of electrons, what is oxidation and reduction
Oxidation is loss of electrons
Reduction is gain of electrons
what does an oxidising agent do in terms of electrons
accept electrons
what does a reducing agent do in terms of electrons
donate electrons
what is the oxidation state of hydrogen
+1 except in metal hydrides where it is -1
what is the oxidation state of Group 1
always +1
what is the oxidation state of Group 2
always +2
what is the oxidation state of Group 3
always +3
In the thermite reaction Fe2O3 + Al -> Fe + AlsO3. what is oxidised and what is reduced
Fe is reduced from +3 to 0
Al is oxidised from 0 to +3
what are the 3 nucleophiles used in nucleophilic substitution reaction
Hydroxide
Cyanide
Ammonia
why is excess ammonia used in nucleophillic substitution reaction
to reduce the chance of the amine taking part in further substitution reactions
what are elimination reactions
when haloalkanes can react with hydroxide ions in an alternative mechanism. instead of producing an alcohol we produce an alkene
what happens if you react sodium/potassium hydroxide with a haloalkane
both nucleophillic substitution and elimination reactions.
how do you favor an elimination reaction
> concentrated NaOH/KOH
ethanol as solvent
high temp
how do you favor nucleophillic substitution reaction
> more dilute NaOH/ KOH
water as solvent
Low temp
what do the hydroxide ions act as in elimination reactions
a base
what do the hydroxide ions act as in nucleophillic substitution reactions
a nucleophile
what is critical for E/Z isomerism to exist
A must not = B and C must not = D
E isomerism
> trans
> opposite look like a Z
Z isomerism
> cis
> next to look like a E
what do electrophillic addition reactions happen with
> Halides eg HBr and HI
Bromine
H2SO4
what is a reducing agent
electron donor
what is an oxidising agent
electron acceptor
give to features of a reaction at equilibrium
> rate of forward = rate of backwards
> net. conc is the same
deduce what happens to the equilibrium when…
> the equilibrium will move to the (left/right)
because the (forward/backwards) reaction is …
to oppose the change (of…)
What will happen to the equilibrium if the pressure is increased
move to the side with the fewest moles of gas
what will happen to the equilibrium if the temp is increased
it moves to the side that is endothermic
what will happen to the equilibrium if a catalyst is added
nothing
how do you work out half- equations
FEW-H~
what are the 3 stages of free radical substitution reactions
1] initiation
2] propagation
3] termination
Initiation
UV light causes homolytic fission and one elctron goes to each atom
what is a free radicals properties
very reactive
high energy
propagation
Cl* + CH4 -> CH3* +HCL
or
CH3* + Cl2 -> CH3Cl + Cl*
> if you start with a * you end with an *
Termination
Cl* +Cl* -> Cl2 or CH3* + Cl* ->CH3Cl or CH3* + CH3* -> CH3CH3
Ozone
O3
what does the Ozone exist in
a natural equilibrium with O2
Why are CFC’s bad
they form Cl free radicals when exposed to UV in the upper atmosphere
> CFCl3 -> Cl* + CFCl2
these free radicals react with the Ozone
what are the two propagation steps in the CFC reaction with the ozone
1] O3 + Cl* -> ClO* + O2
2] ClO* + O3 -> 2O2 + Cl*
what is the overall reaction for the CFC reaction with the ozone
2O3 -> 3O2
what can we say the Cl* does to the ozone layer
catalyses the conversion of ozone into O2
primary alcohols
1 C bond
O-H at the end
secondary alcohols
2 C bonds
O-H at chain
tertiary alcohols
3 c bonds
O-H at branch
primary alcohols are oxidised to…
aldehydes (CH2C=OH + H2O)
secondary alcohols are oxidised to…
ketones (CH3C=OCH3 + H2O)
an Aldehyde is oxidised to…
a carboxillic acid
what can we say about carboxillic acids and Ketones
they do not easily oxidise further because it would require a C-C bond to break rather than a H-C bond
