18 Kinetics Flashcards
what are the main factors that affect the rate of a chemical reaction
temperature concentration pressure surface area catalysts
rate of reaction
change in concentration ( of any of the reactants or products) with unit time
rate of a and b
a/b = change in concentration / time
initial rate
t=0
also at the start you know all the concentration
bromine and methodic acid
Br2 + HCO2H. —– 2Br- +2H+ + CO2
starts brown and ends colourless
colorimeter can be used used to measure the decreasing concentration of bromine
rate expression
a mathematical expression showing how the rate of a chemical reaction depends on the concentration of varies chemical species involved
only includes the species that affect the rate for reaction
rate constant
K
different for every reaction and varies with temperature
order of reaction
In the rate expression, this is the sum of the powers to which the concentrations of all the species involved in the reaction are raised ( e.g. add up all the powers)
plotting a graph of rate against time
horizontal line
rate is unaffected
zero order
plotting a graph of rate against time
sloping straight line through the origin
order 1
plotting a graph of rate against time
not a straight line
order greater than 1
can find out if it is two by plotting the rate against concentration squared and if this is a sloping straight line through the origin then the order is 2
iodine clock reaction
used to measure the Arte of reaction between hydrogen peroxide and potassium iodide in acidic conditions to from iodine
reaction can be times by adding a known number of moles of sodium thiosulfate to the reaction mixture along with some starch
effect of temperature on k
small change in temperature produces large change in reaction rates. ( rough rule is that for every 10k rise in temperature the rate of reaction doubles )
increase in temperature = increase in rate of reaction (k)
why the rate constant depends on temperature
temperature is a measure of the average kinetic energy of particles
particles will only react together if their collision have enough energy to start bond breaking ( activation energy)
as the temperate increase a greater proportion of molecules have enough energy to react.
Arrhenius equation
K = A e^(-Ea/RT)
