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Higher Chemistry Unit 1
Beschreibung
Highers Highers (Chemistry) Mindmap am Higher Chemistry Unit 1, erstellt von alltimeclara am 26/01/2015.
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higher chemistry
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highers
chemistry
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Zusammenfassung der Ressource
Higher Chemistry Unit 1
Reaction rates
Affected by
temperature
the average kinetic energy of the particles in a substance
an energy distribution diagram could be useful
only the particles in the shaded area have enough energy to collide successfully
concentration
increasing concentration causes more collisions
particle size
the bigger the surface area the faster the reaction
catalysts
speed up chemical reactions
two types
homogeneous
same physical state as reactants
heterogeneous
different physical state to reactants
ADSORB reactant molecules onto active site surfaces
catalytic poisons bond so firmly to active sites there are no sites for reactant molecules
form an alternative activated complex
therefore provides an alternative reaction pathway
catalysts in industry
iron
used in haber process to make ammonia
platinum
used in oxidation of ammonia to nitrogen dioxide in ostwald process
nickle
used to hydrogenate vegetable oils in the manufacture of margarine
zymase
used in brewing
vanadium oxide
used in contact process to make sulphuric acid
aluminium oxide
used in catalytic cracking
turns long chain alkanes into more useful short chain alkenes
enzymes
biological catalysts
large soluble protein molecules
works best at an optimum temperature and pH
optimum temperature in human bodies is 37*C
can be denatured (changes shape) at too high temperatures or pH's
collisions
may form an activated complex
for a chemical reaction to occur, reactant particles must collide
to increase reaction rate, number of successful collisions must be increased
Activation energy is the minimum kinetic energy needed for a successful collisiom
the difference between the energies of the activated complex and the reactants.
highly unstable dpecies formed during a reaction as old bonds break and new bonds form
the minimum energy needed to form an activated complex
Activated complex is the minimum energy needed to cause a chemical reaction
1/t
measured in s-1
Enthalpy
combustion
the energy released during complete combustion of one mole of oxygen
neutralisation
the energy change when an acid an alkali cancel each other out to form one mole of water
solution
the energy change when one mole of substance dissolves in water
heat intake/outtake
exothermic
gives out heat energy because energy is released to surroundings
products have LESS energy than reactants
ΔH is negative
endothermic
takes in heat energy because energy is absorbed from surroundings
products have MORE energy than reactants
ΔH is posit8ive
cannot be measured directly
we can only measure the change in energy
ΔH
potential energy diagrams
Patterns in the Periodic Table
elements in the same group have same number of outer electrons; similar chemical properties
as you go along a period , an additional proton is added to the nucleus
covalent radii
along a period atoms get SMALLER
increasing number of protons in nucleus attract the electrons more strongly pulling them inwards
down a group atoms get BIGGER
there are more electron shells
ionisation energy
INCREASE along a period
increasing nuclear charge makes it harder to remove electrons
DECREASES down a group
outer electrons are further from the nucleus and are screened from nuclear attraction y more inner electron shells
the energy needed to remove one mole of electrons from one mole of atoms
electronegativity
a measure of the ability to attract electrons in a bond
elements at the top right of the table are very electronegative
elements a the bottom left are the least electronegative
Bonding, Structure, properties
we can use electronegativity to make predictions about the bonding between atoms
IONIC = very different electronegativites
COVALENT = very similar electronegativities
POLAR = fairly different electronegativites
metalls
delocalised outer electrons are free to leave the metal atoms
elements
nonmetals
pure covalent bonding, atoms have identical electronegativities
structure
discrete covalent
sulphur
S8
phosphorus
P4
intermolecular/intramolecular
intermolecular
hydrogen bonding
polar bonds formed between hydrogen and fluorine, nitrogen or oxygen
strongest of the intermolecular bonds
raises the boiling point
bonding BETWEEN molecules
van der waals forces
molecules become temporarily polar due to a momentary lack of symmetry in the electrons
intramolecular
bonding WITHIN molecules
covalent bonding
The Mole
relative formula mass
contains 6.02x10^23 particles
volume
approximately 24L unless stated otherwise
Calculations
enthalpies
combustion
ethanol
solution
nutralisation
PPA's
PPA 1
effect of concentration on reaction rate
H2O2 + 2H(+) + 2I(-) ----> 2H2O + I2
sharp colour change
starch turns black to blue
PPA 2
effect of temperature on reaction rate
5(COOH)2 + 6H(+) + 2MnO4(-) ----> 2Mn(2+) + 10CO2 + 8H2O
acidified potassium permanganate = purple to colourless
all experiments identical except for twmperature
evaluation
dry beakers to avoid affecting concentrations
accurate experiment not possible at room temperature due to gradual colour change
PPA 3
enthalpy of combustion of ethanol
Medienanhänge
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