CHAPTER 3
Kinetics and Transport
in Nanoscience
OVERVIEW
In the previous chapter, we learned about thermodynamic properties and
the relative stability of reactants and products and how to quantify the
spontaneity of a chemical reaction based on thermodynamic state functions such as Gibbs energy. However, thermodynamics does not provide
insight on how long a reaction takes to reach equilibrium. Even though a
reaction may have a negative Gibbs energy change, it may proceed very
slowly. For example, bulk iron will spontaneously rust (oxidize) when
exposed to air, but the reaction may take many years, while iron
nanoparticles may oxidize very quickly. This chapter is concerned with
how quickly chemical reactions occur and what we can learn about how
reactions occur from the rates at which they occur. Chemical kinetics,
the study of the rates of reactions and the implication of these rates, relies
on the experimental observation of reactions and the effects of changing
conditions on their rates. This chapter also makes an important connection between rates of chemical reactions, transition states, and the
thermodynamic properties for processes at equilibrium. The final section
of the chapter considers the effects of particle diffusion on reaction rates,
which is important for nanoscale systems.
3.1 RATES OF CHEMICAL REACTIONS
3.1.1 The Rate of Reaction
During the course of a chemical reaction, reactants are consumed and
products are formed. The reactant concentrations decrease and the product
concentrations increase until equilibrium is reached. The rate of reaction
can be quantified by measuring how the concentrations of the reacting
Kinetics and Transport
in Nanoscience
OVERVIEW
In the previous chapter, we learned about thermodynamic properties and
the relative stability of reactants and products and how to quantify the
spontaneity of a chemical reaction based on thermodynamic state functions such as Gibbs energy. However, thermodynamics does not provide
insight on how long a reaction takes to reach equilibrium. Even though a
reaction may have a negative Gibbs energy change, it may proceed very
slowly. For example, bulk iron will spontaneously rust (oxidize) when
exposed to air, but the reaction may take many years, while iron
nanoparticles may oxidize very quickly. This chapter is concerned with
how quickly chemical reactions occur and what we can learn about how
reactions occur from the rates at which they occur. Chemical kinetics,
the study of the rates of reactions and the implication of these rates, relies
on the experimental observation of reactions and the effects of changing
conditions on their rates. This chapter also makes an important connection between rates of chemical reactions, transition states, and the
thermodynamic properties for processes at equilibrium. The final section
of the chapter considers the effects of particle diffusion on reaction rates,
which is important for nanoscale systems.
3.1 RATES OF CHEMICAL REACTIONS
3.1.1 The Rate of Reaction
During the course of a chemical reaction, reactants are consumed and
products are formed. The reactant concentrations decrease and the product
concentrations increase until equilibrium is reached. The rate of reaction
can be quantified by measuring how the concentrations of the reacting