Rate Equations Flashcards
What is the rate of reaction?
- how fast reactants are converted in products
What does rate of reaction depend on?
- concentrations of the reactants
- rate constant
What is the equation for total order?
= m + n
What is the definition of zero order
- the concentration of this species has no impact on rate
- shown graphically as a horizontal line
- Rate = K
What is first order?
- the concentration of the species and rate are directly proportional
- doubling concentration doubles the rate
- rate = K[A]
What is second order?
- rate is proportional to the concentration squared
- doubling the concentration will increase the rate by four
- rate=k[A]2
What does the Arrhenius equation show?
- That the rate constant (k) and temperature are related exponentially
What is the Arrhenius equation?
What is the overall rate determined by?
- the slowest step of the reaction
- therefore rate equation contains all species involved in the stages up to and including rate determining step
How can rate equations be determined experimentally?
- by monitoring concentration of a reaction mixture over time
How can a concentration-time graph be used to find the rate
- by drawing a tangent at t=0
- only time where exact concentration is known
How do you get a set of data for concentration and ror
- repeat at varying concentrations
- plot rate against concentration graph
What is the decomposition of hydrogen peroxide equation
2H2O2 -> 2H2O + O2
What is the method for the decomposition of hydrogen peroxide reaction
- Using a measuring cylinder, measure 5cm3 of 20 volume H2O2 into conical flask
- Using a measuring cylinder, measure out 45cm3 of water and add to conical flask
- Weight on approximately 0.25g of MnO2 into weighing boat
- Add the MnO2 to the conical flask, insert the bung and start stopwatch
- Record volume of gas every 15 seconds for 3 minutes, until 50cm3 of oxygen is produced
What does the hydrogen peroxide decomposition reaction do?
- using a continuous method to help determine the order of reaction with respect to a given reagent
What are limitations of the hydrogen peroxide reaction?
- changes in oxygen are hard to calculate (less accurate) - use reactants with higher concentration
- misreading volume, use a weighing balance instead
- o2 is soluble
What is the equation of iodine and propanone?
- I2 + CH3COCH3 -> Ch3COCH2I + H+ + I-
- only reacts in the presence of an acid catalyst (Hcl)
How do we use absorbance to calculate rate?
- as the reaction of iodine and propanone proceeds the brown colour fades as iodine is used up
- absorbance is proportional to the concentration of the iodine (beer lambert law)
What is the method of the calorimetry practical
- Calibrate calorimeter with curette full of distilled water
- Set the filter to blue light for maximum absorption
- Measure out 2cm of HCl, 5cm I2 and 10cm of H2O into small beaker
- Add 5cm3 of propanone, swirl immediately and transfer to cuvette
- Start calorimeters and record absorbance every 10 seconds
What is the rate equation for the calorimetry reaction?
- rate=k[H+][CH3COCH3]
What graph is used to determine rate in the calorimetry experiment
- absorbance over time
- proportional to concentration over time
What reaction occurs in the quenching reaction?
- CH3COCH3 + I2 -> Ch3COCH2I + HI
Quenching ionic equation:
- H+ + HCO3- -> CO2 + H2O
Titre equation:
- I2 + 2S2O32- -> 2I- + S4O62-
How are samples quenched?
- poured into sodium hydrogen carbonate solution
- neutralises acid catalyst
What are other methods used to quench a reaction?
- rapid cooling
- dilution
What is the procedure for quenching?
- place 30cm3 of sodium hydrogen carbonate solution into fixed conical flasks
- fill burette with sodium thiosulfate solution
- mix equal parts of propanone and sulfuric acid into a conical flask. Measure out 50cm of iodine solution. Mix reactants and immediately time reaction
- after 1 min, withdraw 10cm3 of mixture using pipettes. Run contents into one conical flaks and titrate until pale yellow. Add starch solution and titrate until colourless.
- repeat every 3 mins
- plot titre against time
What is the equation of hydrogen peroxide reacting with iodide ions?
H2O2 + 2H+ + 2I- -> I2 + 2H2O
Write the equation for iodine and thiosulphate ions
I2 + 2S2O32- -> 2I- + S4O62-
Why is a blue-black colour appear?
- further iodine produced in the reaction which has not been reacted are detected by starch indicator
As the same number of moles of thiosulphate ions are added to each reaction…
- The appearance of blue-black colour represents the extent of the reaction
- so initial rate of reaction is proportional to 1/t
What is the iodine clock procedure?
- use pipettes and brunettes to mix all reactants in conical flask except hydrogen peroxide
- use burette to measure 10cm3 of hydrogen peroxide
- pour h2o2 into conical flask and swirl - start stopwatch
- record time for blue colour to appear
- repeat
1/time taken = rate
What are three experiments to measure initial rates?
- disappearing cross
- doing the same reaction at 10 different conc, 10 times
- iodine clock
