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Chemical equilibrium and chemical kinetics

Dennis Sherwood and Paul Dalby

in Modern Thermodynamics for Chemists and Biochemists

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, ... More

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, expressing the total Gibbs free energy of a reaction mixture at any time as the sum of the instantaneous Gibbs free energies of each component, as expressed in terms of the extent-of-reaction. The equilibrium reaction mixture is then defined as the point at which the total system Gibbs free energy is a minimum, from which concepts such as the equilibrium constant emerge. The chapter also explores the temperature dependence of equilibrium, this being one example of Le Chatelier’s principle. Finally, the chapter links thermodynamics to chemical kinetics by showing how the equilibrium constant is the ratio of the forward and backward rate constants. We also introduce the Arrhenius equation, closing with a discussion of the overall effect of temperature on chemical equilibrium.Less

Given Enough Time …

Toby Tyrrell

in On Gaia: A Critical Investigation of the Relationship between Life and Earth

This chapter examines James Lovelock's assertion that the Earth's atmosphere is a biological construct that is distinctly different from any expected abiotic chemical equilibrium. This claim can be ... More

This chapter examines James Lovelock's assertion that the Earth's atmosphere is a biological construct that is distinctly different from any expected abiotic chemical equilibrium. This claim can be broadened to the wider claim that Earth's environment bears the definite and considerable imprint of biological processes and is distinctly different from the environment that would be present if Earth did not possess life. Based on the evidence covered in this chapter, from atmosphere and oceans, Lovelock was clearly correct to claim that the coexistence of oxygen and methane in Earth's atmosphere is evidence of life, and that life can alter the planet. Other examples that could also be used as evidence to prove this point include the effects of vegetation in creating and stabilizing soils, the effects of plant transpiration on the cycling of water, and the fossil evidence for the effects of diatoms on silicon concentrations.Less

Thermodynamics and Transport Properties

Thorvald Abel Engh, Geoffrey K. Sigworth, and Anne Kvithyld

in Principles of Metal Refining and Recycling

The fundamentals of thermodynamics are reviewed, focusing on the chemistry of high-temperature metals, oxides (slags), and salts. Thermochemical data are provided for important molten metals: the ... More

The fundamentals of thermodynamics are reviewed, focusing on the chemistry of high-temperature metals, oxides (slags), and salts. Thermochemical data are provided for important molten metals: the free energies of solution of alloy elements, and interaction coefficients. Standard free energies of reactions are also provided, so the reader may calculate important chemical equilibria. Example calculations are provided for the deoxidation of steel. The removal of sulfur and phosphorus are also described. The second half of the chapter considers fundamental aspects of important physical properties: viscosity, surface tension, diffusion, and thermal and electrical conductivity.Less

GAS KINETICS

Norman F. Ramsey

in Molecular Beams

This chapter derives methods for calculating the effusion of molecules from sources with apertures that are narrow and short. Corrections are given for long channeled apertures of various shapes. The ... More

This chapter derives methods for calculating the effusion of molecules from sources with apertures that are narrow and short. Corrections are given for long channeled apertures of various shapes. The intensity of a molecular beam can then be calculated. The procedure for calculating the shape of a molecular beam with given source and collimator widths is given. The calculations of various characteristic velocities of molecules in a volume of gas and in a molecular beam are given and discussed along with some experiments measuring the velocities. A number of experiments measuring molecular scattering in gases have been carried out with various methods of analysis. Reflection and diffraction of molecules at surfaces have been studied. Molecular beams have also been used to study chemical equilibrium, ionization potentials, and as sources for optical and microwave spectroscopy.Less

Reactions in solution

Dennis Sherwood and Paul Dalby

in Modern Thermodynamics for Chemists and Biochemists

Another key chapter, examining reactions in solution. Starting with the definition of an ideal solution, and then introducing Raoult’s law and Henry’s law, this chapter then draws on the results of ... More

Another key chapter, examining reactions in solution. Starting with the definition of an ideal solution, and then introducing Raoult’s law and Henry’s law, this chapter then draws on the results of Chapter 14 (gas phase equilibria) to derive the corresponding results for equilibria in an ideal solution. A unique feature of this chapter is the analysis of coupled reactions, once again using first principles to show how the coupling of an endergonic reaction to a suitable exergonic reaction results in an equilibrium mixture in which the products of the endergonic reaction are present in much higher quantity. This demonstrates how coupled reactions can cause entropy-reducing events to take place without breaking the Second Law, so setting the scene for the future chapters on applications of thermodynamics to the life sciences, especially chapter 24 on bioenergetics.Less

Removal of Dissolved Impurities from Molten Metals

Thorvald Abel Engh, Geoffrey K. Sigworth, and Anne Kvithyld

in Principles of Metal Refining and Recycling

Impurities are transferred out at the boundary of the liquid. Velocities normal to the boundary are small. Therefore, for efficient removal contact areas and times should be large. Transfer depends ... More

Impurities are transferred out at the boundary of the liquid. Velocities normal to the boundary are small. Therefore, for efficient removal contact areas and times should be large. Transfer depends on the chemical and physical properties of the liquid and the phase that captures the impurities at the boundary. This phase may be a liquid, gas (vacuum) or solid. Properties can be described in terms of equilibrium and empirical mass transfer coefficients. Vacuum may be applied to remove volatile elements. Refining can be carried out by partial solidification or fractional crystallisation, using the segregation that occurs during freezing of an alloy. Finally, an element can be added to form a reactive compound followed by removal of the compound by sedimentation or filtration.Less

Chemical reactions

Andrew M. Steane

in Thermodynamics: A complete undergraduate course

The use of chemical potential in basic chemistry is introduced. Chemical equilibrium is discussed, and the law of mass action derived. The Van ‘t Hoff equation is derived.