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Chapter

Cover Making the Transition to University Chemistry

Kinetics  

This chapter discusses rates of reactions in kinetics. The rate of reaction is based on the rate of change of concentration per unit time. The activation energy for a reaction is the minimum energy necessary for a collision to lead to a successful reaction. The rate of reaction, then, depends on the concentration of the reactants, temperature, presence of a catalyst, and state of subdivision. The Maxwell–Boltzmann distribution pins the number of molecules in a gas with given energy against energy. On the other hand, the Arrhenius equation measures the activation energy on how the rate constant depends on the temperature.

Chapter

Cover Chemistry3

Gases  

This chapter traces the interest of chemists in gases, noting that, in historical terms, the study of gases involved some of the earliest and most important scientific measurements and helped to develop many ideas of atomic theory and stoichiometry. In more modern terms, many reactions that are important in the chemical industry involve reactions between gases. The chapter describes the experimental evidence for the relation between n, p, V, and T in the ideal gas equation and the assumptions underlying the kinetic theory of gases. It talks about the Maxwell–Boltzmann distribution of molecular speeds and its dependence on the temperature and the molar mass of the gas and elaborates what is meant by effusion and application of Graham's law. It also highlights the role of models in explaining the behaviour of chemical systems and the difference between an empirical approach and a theoretical approach.

Chapter

Cover Atkins’ Physical Chemistry

Collision theory  

This chapter explores collision theory, which is the simplest quantitative account of reaction rates and can only be used for the discussion of reactions between simple species in the gas phase. It shows how basic collision theory considers the impact of one molecule on another, taking into account how the resulting excitation energy accumulates in the bond where it is needed. It also discusses the bimolecular gas-phase reaction that takes place when reactants collide, provided their relative kinetic energy exceeds a threshold value and certain steric requirements are fulfilled. The chapter draws on the kinetic theory of gases, especially the expression for the mean speed of molecules and extends the account of the Lindemann–Hinshelwood mechanism of gas-phase reactions. It draws on the Maxwell–Boltzmann distribution of molecular speeds.

Chapter

Cover Atkins’ Physical Chemistry

The kinetic model  

This chapter examines the kinetic model, which assumes that a gas consists of molecules of negligible size in ceaseless random motion and obeying the laws of classical mechanics in their collisions. As well as accounting for the gas laws, this model can be used to predict the average speed at which molecules move in a gas, and its dependence on temperature. The chapter then looks at pressure and molecular speeds, the Maxwell–Boltzmann distribution of speeds, and mean values. The Maxwell–Boltzmann distribution of speeds gives the fraction of molecules that have speeds in a specified range. The chapter also considers the collision frequency and the mean free path. The collision frequency is the average number of collisions made by a molecule in a period of time divided by the length of that period. Meanwhile, the mean free path is the average distance a molecule travels between collisions.