aqa as chemistry unit 2


Flashcards on aqa as chemistry unit 2 , created by jamie_m on 25/05/2015.
Flashcards by jamie_m, updated more than 1 year ago
Created by jamie_m almost 9 years ago

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Question Answer
Initiation in free radical subs production of free radicals - breaks homolytically - photochemical reaction
Propagation reaction between a free radical and a molecule to make another free radical
Termination (FRS) reaction between two free radicals making an unreactive molecule
Standard enthalpy of formation the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states, under standard conditions
why is the enthalpy of formation of oxygen gas zero? it is an element, in its standard state - can be applied to all other elements
Mean bond enthalpy Standard molar enthalpy change of bond dissociation is the energy required to break a specific covalent bond. This varies between compounds, so an average is used
Standard enthalpy change of combustion Enthalpy change when one mole of a compound is completely burnt in oxygen under standard conditions
Enthalpy change Heat energy change measured at constant pressure
Hess's Law the enthalpy change for a reaction is independent on the pathway taken from the reactants to products
Oxidation (in terms of electrons) loss of electrons
Reduction (in terms of electrons) gain of electrons
Oxidising power - trend in the halogens - decreases going down the group - want to gain electrons. This is shown by displacement reactions
Halide ions as reducing agents - increases going down the group - want to lose electron - larger = easier to lose electron
Halogens - Ionic radius increases going down the group, increasing reducing power
why is the ionic radius larger than the normal atom? (in negative ion) added electron repels others so radius gets larger
Disproportionation redox reaction in which the oxidation number of some atoms of a particular element increases and others of the same element decrease
conditions needed for elimination - no water present - hydroxide is dissolved in ethanol and mixed with haloalkane - hot - tertiary haloalkane
conditions needed for nucleophilic subs - presence of water - cold - primary haloalkane
geometrical isomer same structural formula but bonds are arranged differently in space
why are alkenes not used as fuels? their reactivity makes them useful for other purposes
electrophile - attracted to double bond - electron pair reciever - form carbocations
positive inductive effect alkyl groups e.g. CH3 or C2H5 have a tendency to release electrons
Electrophilic addition steps 1. formation of carbocation by electrophilic additon 2. rapid reaction with a negative ion
define: polymer - long chain molecule made from many monomers - forms a chain with a very high Mr
why do alcohols have higher melting and boiling points than alkanes of a similar Mr? addition of -OH means that there is hydrogen bonding between molecules
why are shorter chain alcohols soluble in water? hydrogen bonding means that hydrogen bonds can form between water and -OH
Temperature - the average kinetic energy of particles in a system - particles move faster, KE goes up and so does temp - temperature is independent of the number of particles present
Heat - total energy of all particles present - dependent of amount of substance present - flows from high to low temp
Specific heat capacity amount of heat needed to raise the temperature of 1g of substance by 1K
How does a flame calorimeter reduce heat loss? - spiral chimney is made of copper - flame is enclosed - fuel burns in pure oxygen, rather than in air
bond dissociation energy the enthalpy change required to break a covalent bond with all species in a gaseous state
Gangue unwanted materials from ores such as clay and rock
Ore an ore is a substance that contains enough metal for it to be economically viable to mine and extract
Roasting process of converting sulfide ores to oxides by heating in air
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