topic 9 + 16 kinetics 1 and 2 Flashcards
effect of changing conc of reactants on rate
- increase conc = more particles per unit volume
- more frequent successful collisions
- increased rate
effect of changing pressure of reactants on rate
- same no. particles per smaller unit volume
- more frequent successful collisions
- increased rate
effect of changing temperature of reactants on rate
- increases KE of reactants
- move faster
- more frequent successful collisions
- more collisions have energy >= Ea
effect of changing SA of reactants on rate
- increased SA
- more particles able to react per unit volume
- more frequent successful collisions
- increased rate
activation energy
minimum amount of energy needed by reactant particles for the reaction to take place
endothermic
take in energy
exothermic
release energy
activation energy in endothermic
LARGER than exo
successful collision is
- collision in the correct orientation
- energy greater than or equal to activation energy
meausring rate of reaction (mass of gas lost)
- use a BALANCE
- LIMITATION: gas must be dense enough or change in mass is too small to measure [look at mr]
measuring rate of reaction (volume of gas produced)
- gas syringe
- collection over water [as long as gas not water soluble]
measuring rate of reaction (concentration changes)
-take a sample at a certain point
- quench
- titrate
measuring rate of reaction (disappearing cross)
limitation: subjective, only 1 piece of data for analysis
initial rate graph tangent
at time = 0
what does the Maxwell-Boltzmann curve show
distribution of energies of particles at a certain temperature
higher temp on boltzmann curve
- peak lower and to the right
- above initial
how does a catalyst work
- increase rate of reaction by providing an alternative pathway with a lower activation energy
homogeneous catalyst
- catalyst in the same phase as the reactants (same state)
heterogeneous catalyst
- catalyst in a different phase to the reactants (different state)
how to show effect of catalsyt on maxwell boltzmann curve
move activation energy line to the left (more particles have Ea)
5 ways of measuring rat eof reaction
- mass lost
- volume of gas produced
- colorimetry
- pH change
- changes in electrical conductivity
first order reactant
rate DIRECTLY PROPORTIONAL to conc of reactant
fractional order
reaction involves multiple steps
0 order
changing conc of reactant has no effect on rate
- not in rate equation
2nd order
rate directly proportional to SQUARE of conc of chemical
overall order
add together the orders of each reactant
units of rate
mol/dm3/s
colorimetry for coloured precipitates
not allowed
rate determing step
slowest step in the reaction
uses reactants in equation
arrhenius equation
k = Ae^(-Ea/RT)
r
ideal gas constant
8.31J/(mol*k)
Ea unit in equation
J/mol
graph for arrhenius
1/Temperature [k] (x axis)
ln k (y axis)
gradient arrhenius
m = -Ea/R
rate of reaction defintion
rate of decrease of concentration of reactants
overall order of reaction defintion
sum of the powers to which concentration terms are raised in the ocerall rate equations
why can you not use just stoichiometric equation to determine order
the rate equation only includes the species involved in the rate equation
give a reason why the rate equation shows the reaction cant happen in one step
- x molecules in stoichiometric but less in rate
- collisions with 2+ particles unlikely
apparatus to remove samples for quenching
volumetric pipette
why can you use volume of titre - initial volume of titre on y axis for graph
volume is proprotional to concentration of reactant
purpose of putting ice in flask before titrating
- quenches reaction
- slows it down significantly, or reaction would continue produicng x product
OR NO
- reaction slow
- no catalyst used
unit of gradeint
K
why is Ea so high
- lots of energy required for reaction to start
- to break the strong bonds
- shows a slow rate of reaction
purpose of phenol in experiment
- reacts with bromine
- when finished, excess bromine bleaches indicator, allowing a point to minotor progress if reaction
why is total volume of reactant kept constnat (think serial dilution)
so that volume reactant is proprotional to concentration
graph of conc v 1/time
assumption needed to use 1/time for rate?
- progress point happens early in reaction
- where [reactant] against time is almost linear
- so that the tangent is the same as change in conc/time (rate)
if incorrect volume measured, should this be discarded?
NO
- plot at correct point on graph
- ensure total volume still constant
why measure into boiling tube from burette before reaction mixture
- burette too slow to add
- start time inaccurate
changes to procedure to get overall rate equation
- repeat, varying [other reactatns]
- keeping all other values constant
labels on maxwell boltzmann curve
x axis = energy, E
y axis = proportion of particles with energy
why does a catalyst have no effect on the products in the reaction
- increases the rate of the forwards and backwards reactions
how to check a catalyst works and isnt used up
- filter solid
- dry
- reweigh (constant)
- repeat to see if rate still decreased
why is a hetergenous solid catalyst good for a gas reaction
provides a surface for the reaction
why is initial rate graph method flawed
- harder to draw the tangent for initial than it is for max
why is volume of gas a bit higher in high temperatures
vol gas exapnds at high temperatres
graph time (x axis) conc (y axis) how to find rate
tangent at t=0
increasing pressure effect on heterogeneous catalysts
- little effect
- reactin occurs on surface
- active sites already saturated with reactants
when can you use change in volume of gas to investigate rate
- CHANGE IN NUMBER OF MOLES OF GAS
WHATW CHANGES THE RATE CONSTANT
temperature
arrhenius GRAPH
- used to find activation energy
- 1/t on x axis, ln k on y axis
purpose of sodium hydrogen carbonate in propanone iodine reaction
- neutralises H+
- quenches reaction
suggest why in an exothermic reaction the rate might be anomolously higher ?
- exothermic reaction
- heat released
- increases ke, more frequent successful collisions with e>= ea
