Rate Equations: Determination of Rate Equation - Measuring Rate

Question 1

What is a reaction rate?

Answer 1

• Rate is the change in the amount of reactants or products per unit of time

Question 2

List various methods used to measure the rate of a reaction

Answer 2

• Measuring gas volume
• Observing changes in pH
• Observing colour change
• Measuring loss of mass

Question 3

What is continuous monitoring?

Answer 3

• Measuring amount of product/reactant at regular time intervals
• Can be used to calculate how rate changes over time

Question 4

How can gas volume be measured?

Answer 4

• Collect gas in gas syringe

- Record volume of gas at regular time intervals

Question 5

How would you use the gas volume results to calculate the reaction rate?

Answer 5

• Plot a concentration-time graph
• Use ideal gas equation to calculate number of moles of gas
• Use molar ratio to calculate concentration of an aqueous reactant

Question 6

How can changes in pH be measured to calculate the reaction rate?

Answer 6

• If reaction uses up or produces H+ ions, the pH will change
• Use a pH probe to measure the pH of the solution at regular intervals and calculate the concentration of H+ ions
• [H+] = 10^-pH

Question 7

How can colour changes be measured?

Answer 7

• Track colour change using a colorimeter
• Colorimeters measure the absorbance (amount of light of particular wavelengths absorbed) of the solution
• Measure absorbance of solution at regular time intervals

Question 8

How can colour changes be used to calculate the reaction rate?

Answer 8

• Plot a calibration curve - graph of known concentration against absorbance
• Use calibration curve to convert absorbance at each time point into a concentration

Question 9

How can loss of mass be measured?

Answer 9

• If a gas is produced, the system will lose mass

- Measure mass at regular intervals with a mass balance

Question 10

How can mass loss be used to calculate the reaction rate?

Answer 10

• Calculate mass lost at each time interval
• Write chemical equation for reaction
• Calculate number of moles of mass are lost at each time interval using, moles = mass / Mr
• Calculate number of moles of a reactant you had initially using, concentration = moles / volume
• Use molar ratio of reactant:gas
• Calculate number of moles of reactant at a time using, initial moles of HCl - moles of gas
• Repeat at each time point
• Plot concentration-time graph