CH10 - Kinetics

Question 1

what is the quasi-equilibrium approach?

Answer 1

Why? To solve complications with pathways which mineral systems pass during transition from initial to final state
What? Define an activated state which has some intermediate configuration, allowing for a free energy curve. Initial and final must be at a minima and intermediate at a maxima

Question 2

what does the quasi-equilibrium approach quantitatively explain?

Answer 2

• Persistence of metastable states being large compared to mean free energy
  
  • Reaction rate independent of driving force
  • Effect of catalysts
    Slow rate of some transformations (only some atoms have sufficient free energy to overcome activation energy)

Question 3

why is enthalpy equal to activation energy?

Answer 3

Most solid state reactions at low pressures have small volume changes, thus the change in enthalpy is approximated to the internal energy of the activated state

Question 4

What is activation energy?

Answer 4

The difference between the enthalpy of the transition state and initial state

Question 5

What is rate of transformation controlled by?

Answer 5

Controlled by the number of activated complexes formed, and that the decomposition of these is virtually instantaneous

Question 6

What does activated state explain?

Answer 6

• Metastability (dG large compared to mean free energy)
  
  • Effect of catalysts (lower dG)
    Slow reaction rates in nature (few atoms can overcome the barrier dG*)

Question 7

What does the rate of heterogenous reactions depend on at fixed conditions?

Answer 7

Time; this is because rate depends on composition which are continuously changing as the reaction proceeds

Question 8

Why can we not equate Ea to coarsening?

Answer 8

While coarsening is dependent on diffusion rate, they can not be equated due to the definition of rate constant and its dimensions as well as large uncertainties

Question 9

Why can we not equate Ea to D?

Answer 9

Dimensions of diffusion coefficient D are different to rate constant k. However both are linked to Ea

Question 10

Heterogeneous reactions ?

Answer 10

Involves nucleation and growth of the product phases within the parent phase. Takes place on defects

Question 11

Isokinetic reactions

Answer 11

Related to Avrami equations and refer to situation when a reaction is carried out at a series of temperatures and the plot gives a set of parallel lines

Question 12

where is kinetic energy stored?

Answer 12

Atomic vibrations

Question 13

Where is potential energy stored?

Answer 13

Interatomic bonds