Rate Equations

Question 1

What is the rate of reaction?

Answer 1

• how fast reactants are converted in products

Question 2

What does rate of reaction depend on?

Answer 2

• concentrations of the reactants
• rate constant

Question 3

What is the equation for total order?

Answer 3

= m + n

Question 4

What is the definition of zero order

Answer 4

• the concentration of this species has no impact on rate
• shown graphically as a horizontal line
• Rate = K

Question 5

What is first order?

Answer 5

• the concentration of the species and rate are directly proportional
• doubling concentration doubles the rate
• rate = K[A]

Question 6

What is second order?

Answer 6

• rate is proportional to the concentration squared
• doubling the concentration will increase the rate by four
• rate=k[A]2

Question 7

What does the Arrhenius equation show?

Answer 7

• That the rate constant (k) and temperature are related exponentially

Question 8

What is the Arrhenius equation?

Answer 8

Question 9

What is the overall rate determined by?

Answer 9

• the slowest step of the reaction
• therefore rate equation contains all species involved in the stages up to and including rate determining step

Question 10

How can rate equations be determined experimentally?

Answer 10

• by monitoring concentration of a reaction mixture over time

Question 11

How can a concentration-time graph be used to find the rate

Answer 11

• by drawing a tangent at t=0
• only time where exact concentration is known

Question 12

How do you get a set of data for concentration and ror

Answer 12

• repeat at varying concentrations
• plot rate against concentration graph

Question 13

What is the decomposition of hydrogen peroxide equation

Answer 13

2H2O2 -> 2H2O + O2

Question 14

What is the method for the decomposition of hydrogen peroxide reaction

Answer 14

1. Using a measuring cylinder, measure 5cm3 of 20 volume H2O2 into conical flask
2. Using a measuring cylinder, measure out 45cm3 of water and add to conical flask
3. Weight on approximately 0.25g of MnO2 into weighing boat
4. Add the MnO2 to the conical flask, insert the bung and start stopwatch
5. Record volume of gas every 15 seconds for 3 minutes, until 50cm3 of oxygen is produced

Question 15

What does the hydrogen peroxide decomposition reaction do?

Answer 15

• using a continuous method to help determine the order of reaction with respect to a given reagent

Question 16

What are limitations of the hydrogen peroxide reaction?

Answer 16

• changes in oxygen are hard to calculate (less accurate) - use reactants with higher concentration
• misreading volume, use a weighing balance instead
• o2 is soluble

Question 17

What is the equation of iodine and propanone?

Answer 17

• I2 + CH3COCH3 -> Ch3COCH2I + H+ + I-
• only reacts in the presence of an acid catalyst (Hcl)

Question 18

How do we use absorbance to calculate rate?

Answer 18

• 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)

Question 19

What is the method of the calorimetry practical

Answer 19

1. Calibrate calorimeter with curette full of distilled water
2. Set the filter to blue light for maximum absorption
3. Measure out 2cm of HCl, 5cm I2 and 10cm of H2O into small beaker
4. Add 5cm3 of propanone, swirl immediately and transfer to cuvette
5. Start calorimeters and record absorbance every 10 seconds

Question 20

What is the rate equation for the calorimetry reaction?

Answer 20

• rate=k[H+][CH3COCH3]

Question 21

What graph is used to determine rate in the calorimetry experiment

Answer 21

• absorbance over time
• proportional to concentration over time

Question 22

What reaction occurs in the quenching reaction?

Answer 22

• CH3COCH3 + I2 -> Ch3COCH2I + HI

Quenching ionic equation:
- H+ + HCO3- -> CO2 + H2O

Titre equation:
- I2 + 2S2O32- -> 2I- + S4O62-

Question 23

How are samples quenched?

Answer 23

• poured into sodium hydrogen carbonate solution
• neutralises acid catalyst

Question 24

What are other methods used to quench a reaction?

Answer 24

• rapid cooling
• dilution

Question 25

What is the procedure for quenching?

Answer 25

• 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

Question 26

What is the equation of hydrogen peroxide reacting with iodide ions?

Answer 26

H2O2 + 2H+ + 2I- -> I2 + 2H2O

Question 27

Write the equation for iodine and thiosulphate ions

Answer 27

I2 + 2S2O32- -> 2I- + S4O62-

Question 28

Why is a blue-black colour appear?

Answer 28

• further iodine produced in the reaction which has not been reacted are detected by starch indicator

Question 29

As the same number of moles of thiosulphate ions are added to each reaction…

Answer 29

• The appearance of blue-black colour represents the extent of the reaction
• so initial rate of reaction is proportional to 1/t

Question 30

What is the iodine clock procedure?

Answer 30

• 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

Question 31

What are three experiments to measure initial rates?

Answer 31

• disappearing cross
• doing the same reaction at 10 different conc, 10 times
• iodine clock