16 - Kinetics II

Question 1

What is the rate determining step?

Answer 1

• The slowest step in the mechanism(s) for the reaction

Question 2

What is the order of a reaction?

Answer 2

• The power of which the concentration of reactant species is raised in the rate equation
  example: rate = k[A]^2, is second order

Question 3

How can you measure the rate of a reaction using colorimetry?

Answer 3

• Measure the colour change by looking at the time it takes for the cross to disappear
• Colorimeter is more accurate

Question 4

How can you determine the rate equation of a reaction by experiment?

Answer 4

• Different concentrations of the reactant

- Continuous monitoring of the reaction to plot a graph

Question 5

How do you determine the rate using a graph when axis : x= time y=concentration

Answer 5

• Use the half life method

- Half life time taken for half of the product to be used etc….

Question 6

How to determine the order of a reaction of a rate (1/t y axis) concentration graph?

Answer 6

• 0 order Straight horizontal line
• 1 order Straight diagonal line through origin
• 2 order Curved graph when plotter against [A] nut must check against [A]^2
• 2 order Straight line through origin for 1/t (y axis) and [A]^2 (x-axis)

Question 7

How can you deduce the reaction mechanism from the rate equation?

Answer 7

• Check which molecules are involved in or BEFORE the rate determining step then go from there

Question 8

What is the difference between a homogenous catalyst ad a heterogenous?

Answer 8

• Homogenous : same phase

- Heterogenous : different phase

Question 9

In the Arrhenius equation graph where lnk = (1/T)*(-Ea/R) + lnA (T= Temperature in kelvin) what would be the gradient?

Answer 9

• (-Ea/R) : -ve activation energy over R gas constant