Initial Rate Experiments Flashcards
Define initial rate of reaction
The rate of reaction at the start of the reaction
Describe the initial rates method(3)
– Time how long it takes for set amount of product to form at beginning of the reaction
– Use this data to calculate initial rate of reaction
– Repeat experiment several times changing initial concentration of one of the reactants
What are the three things you have to assume when planning initial rates exepriment?
– The concentration of the other reactants aren’t changing significantly (by having all of the reactants present in excess)
– Temperature stays constant
– Reaction has not proceeded too far when you take measurement
How do you calculate initial rate of reaction?
Initial rate = amount of reactant used a product formed/Time
How do you estimate the initial rate of reaction from the concentration time graph?
Draw a tangent to the curve at t=0 and measure gradient
What is the equation for an iodine clock reaction?
H2O2(aq) + 2I^-(aq) + 2H^+(aq) –> 2H20(l) + I2(aq)
Describe iodine clock reaction experiment(4)
– Small amount of sodium thiosulfate solution and starch added to excess hydrogen peroxide and iodide ions in acid solution
– Sodium thiosulfate added to mixture reacts instantaneously with any iodine
- Once all sodium thiosulfate is used up, remaining iodine and solution will cause starch indicator to turn solution blue black (this is the end point)
- Varying concentration of iodide ions or hydrogen peroxide will give different times of the colour change
How do you clock reactions work?
Measures how time taken for set amount of product to form changes as concentration of a reactant varies
What is the purpose of starch in iodine clock reactions?
An indicator which turns blue black in the presence of iodine
What is good about clock reactions?
– Has an observable and point (the colour change) which tells you when the desired amount of product is formed
