RATES OF REACTIONS Flashcards
4 ways rate can be measured in experiments
The change in pH of a reaction
amount of mass lost
Volume of gas produced
Colorimeter can measure colour change
How to use a colorimeter to measure rate
measure the absorbance and plot a calibration curve of known concentrations of your coloured reactant
can then use the graph to find out unknown concentrations of the reactant
How can rate be found from a graph
it is the gradient of the straight line, or the gradient of the tangent to a curve at a certain time
How to calculate initial rate of reaction
The gradient of the tangent at 0 minutes
How can clock reactions be monitored
prepare the reaction on top of a black cross on a piece of paper
time how long it takes for the cross underneath to no longer be visible, known as the end point
4 assumptions to clock reactions
the temperature of the reaction remains constant
the concentration of reactions doesn’t change significantly during the reaction
reaction has not proceeded too far when the end point is seen
overall we can say the rate remains constant during the time period we are measuring
Iodine clock experiment ionic equation and explanation
H2O2(aq) + 2H+(aq) + 2I-(aq) –> 2H2O(l) + I2(aq)
sodium thiosulfate and starch to excess hydrogen peroxide
sodium thiosulfate reacts immediately with the iodine that is produced, until the sodium thiosulfate runs out, then starch reacts with starch to give a deep blue black colour
Rate equation format and units
Rate = k[A]a[B]b
rate = mol/dm3/s
k = units vary depending on concentration
What is a zero order reactant
one that a change in concentration has no effect on rate
What is a first order reactant
one that a changes in concentration has a proportional effect on rate
What is a second order reactant
one that a change in concentration has a squared proportional change on rate
if it doubles, the rate will be quadrupled
What happens to k when the temperature changes
Increase in temp means an increase in k
decrease in temp means decrease in k
how does k change with different rates
the larger the value of k the faster the rate of reaction
What is the half life of a reactant
time taken for half of the reactant to be used up
half life of first order reactants
half life is independent of concentration so each half life will be the same length
