rate - initial method Flashcards
what is initial rate
the instantaneous rate at the start of a reaction when t=0
what to make sure when doing a clock reaction
not too much time has passes since the start of the reaction - otherwise 1/t not proportional to rate
what are the 2 equations for the iodine clock reaction
H2O2 (aq) + 2I- (aq) + 2H+(aq) → I2 (aq) + 2H2O (l)
2S2O32- (aq) + I2 (aq) → 2I- (aq) + S4O62- (aq)
how can you tell the end of the reaction in iodine clock
blue-black colour of iodine in starch is seen
errors
inaccurate timing of the appearance of the blue colour
adding starch slightly increases the volume which effects the concentrations of the reactants and thus the amount they change over time
what is the disappearing cross experiment
sodium thiosulphate reacts with hydrochloric acid
solid sulfur forms which causes the solution to become opaque
equation for disappearing cross
Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + SO2 (g) + S (s)
how can you turn this into a Arrhenius plot
plot 1/t against ln(1/t)
gradient - activation energy
what is a clock reaction
a reaction in which the conc of a reagent quickly changes after a certain time period – causing a colour change
control variables for clock reaction
volume of reactants
volume of starch + thiosulfate
conc of all the reagents - except iodide ions
temperature
