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Chemistry 130 Chemistry 130 Dr. John F. C. Turner 409 Buehler Hall [email protected] Chemistry 130 Course coverage Ch. 12: Properties of Solutions Ch. 13: Chemical Equilibrium Ch. 15: Acid-base equilibria Ch. 16: Solution Equilibria Spring Break Ch. 17: Thermodynamics Ch. 18: Electrochemistry Ch. 19: Nuclear Chemistry Ch. 20 – 22: Descriptive Chemistry of the elements Ch. 23 – 24: Organic, biological, medicinal and materials chemistry Chemistry 130 Course mechanics Grading Scale Lecture course : 80% 6 quizzes: ~25% 3 exams: ~25% Final Examination: 30% Laboratory course : 20% Grade Cut-offs : A: 80%-100% B+: 78%-79.9% B: 70%-77.9% C+: 68%-69.9% C: 60%-67.9% D: 50%-59.9% F: 0%-49.9% There is no curve; grading is on an absolute scale. There are no dropped quizzes or examinations. Chemistry 130 Course mechanics Additional Help The tutorial center, in Buehler Hall, opposite the General Chemistry office on the 5th floor, is staffed from 9.00 a.m. until 5 p.m. daily during the semester. All Chem 130 students are invited to the three review sessions on Monday, Tuesday and Wednesday 7 p.m. – 10 p.m. Buehler 511. Office hours are held on Monday from 2 – 5 p.m. at Buehler 409. Chemistry 130 Course overview and context The first half of the course will cover: Properties of Solutions Solution Equilibria Chemical Equilibrium Thermodynamics Acid-base equilibria Electrochemistry The key to understanding all of these areas is the study of thermodynamics Chemistry 130 Course overview and context Properties of Solutions Solution Equilibria Chemical Equilibrium Thermodynamics Acid-base equilibria Electrochemistry All of these topics are very important: On a practical level: “Life takes place in solution” - the human body is ~70% water and fluids in the body are solutions Many technologically important materials are solution: Steel Palladium-hydrogen Chemistry 130 Steel Steel is a complicated system, the majority components of which are iron and carbon. Phase diagram for Fe-Fe 3C There are many phases and transitions between phases, with different compositions. Transformation temperatures are also different between different phases. Chemistry 130 Palladium-hydrogen Palladium will absorb very large quantities of H 2 to form a gas-solid solution. H2 This is a very important process for the storage of hydrogen and the so-called 'hydrogen economy' (nothing to do with cold fusion........) Chemistry 130 Course overview and context Science is also a powerful description of the physical world. It is a fundamentally important cultural construction. It is new and it is always wrong and it is always right simultaneously. The Scientific Method A natural law is a sum of human experience in light of experiment, theory and hypothesis It is predictive and testable in all aspects The material in Chem 130 addresses one fundamental property of the description of the physical world – change and the nature of change Chemistry 130 Course overview and context Chemistry is the unique science that contains all the elements of a mathematically rigorous science. It also contain elements of art, in terms of creativity Chemists change the local structure of the universe, in principle at will. The definition of chemistry: “That branch of physical science and research, which deals with the several elementary substances, or forms of matter, of which all bodies are composed, the laws that regulate the combination of these elements in the formation of compound bodies , and the various phenomena that accompany their exposure to diverse physical conditions.” Chemistry 130 Course overview and context Change is an essential aspect of chemistry and chemical change takes place within those natural laws that are well understood. Chemical change is one of the fundamental mechanisms that limit or enable the compass of our lives. Chemistry 130 is partially about the restrictions and allowances that govern chemical change. Chemistry 130 Course overview and context Many changes are spontaneous; many are not. Some hypothetical changes have never been observed. Why? Chemical change involves a change in the number of particles that we observe: H2 C=CH 2 Br 2 Br CH 2 CH 2 Br NaOH aq HCl aq NaCl aq H2 Ol In both of these reaction, we see the reactants disappear and the products appear. What are the rules that govern the destruction and creation, i.e. the chemical interchange of forms of matter? Chemistry 130 Course overview and context In Chem 120, we focused on heat and heat flows that are observed in the course of a chemical reaction. We described these heat flows as either The internal energy, U, at constant volume or The enthalpy, H, at constant pressure Both of these extensive properties are descriptions of the system only Chemistry 130 Course overview and context H2 C=CH 2 Br 2 Br CH 2 CH 2 Br NaOH aq HCl aq NaCl aq H2 Ol However, even though these chemical changes are occurring locally, after we have performed these reactions, there is a little less bromine or sodium hydroxide and a little more 1,2,dibromoethane and sodium chloride in the universe than before. We must consider the universe, from a local perspective (in order not to be too grandiose.....) Chemistry 130 Chemistry 130 Physical Properties of Solutions Dr. John F. C. Turner 409 Buehler Hall [email protected] Chemistry 130 Solutions, solvents and solutes Solutions are extremely important chemical systems in which many reactions and physical phenomena take place. Atmospheric chemistry often, but not always, takes place in solution Formation O2 g h 2O g O2 g O g O3 g Destruction O3 g O g 2O2 g Chemistry 130 Solutions, solvents and solutes A solution is defined as a homogenous mixture of two or more components The major component is called the solvent The other, minor components are called the solutes Solutions can occur in the solid state, the liquid state or the gaseous state The pure components can be solid, liquid or gas prior to forming the solution Chemistry 130 Example 1: Sodium in liquid ammonia Solute Solvent Solution Na s NH 3l low high concentration concentration low conductivity metallic conductivity Chemistry 130 Example 2: Potassium permanganate in water Solute Solvent Solution KMnO 4 s H2 Ol Very powerful oxidant Chemistry 130 Energetics of solution The dissolution of Na in liquid ammonia and KMnO 4 in water both involve solids that are strongly bonded. For Na, m.p. /°C: ~97 b.p. /°C: ~883 resulting in a liquid range of 785 K KMnO 4 decomposes before it melts The forces between particles in both Na and KmnO 4 are strong So why do they dissolve? Chemistry 130 Energetics of solution: Intermolecular forces When considering the solubility or insolubility of a potential solute in a solvent, the first thing to consider are the intermolecular forces There are forces between all atoms in a condensed state i.e. in the liquid or solid state. A perfect gas has no forces between particles and cannot be liquified or solidified; however, all gases can be condensed at some temperature He Ne Ar Kr Xe Rn m.p./ °C [-272.2] -248.59 -189.3 -157.36 -111.7 -71 b.p./ °C -268.93 -246.08 -185.8 -153.22 -108 -61.7 Increasing polarizability Chemistry 130 Energetics of solution: Intermolecular forces All molecules exert weak attractions on one another due to the mutual attraction of nuclei and electrons. These attractive forces are only significant at very short distances. At such small distances the intermolecular repulsion of the electrons on different atoms is also significant. The electrons contained in all atoms and molecules can be perturbed by an electric field, with greater or lesser ease. This property is called polarizability. The electron cloud around an atom or molecule can give an instantaneous dipole any time that the electrons are not distributed perfectly symmetrically. Such a dipole can induce dipoles in other species nearby. Chemistry 130 Energetics of solution: Intermolecular forces The polarizability of a molecule depends on the size of the atoms and how strongly the electrons are bound within the atom. At any instant, the electron density can fluctuate and the distribution can become instantaneously asymmetric. This instantaneous and transient dipole can induce a similar dipole in a neighboring atom or molecule, resulting in a weak attraction Chemistry 130 Energetics of solution: Intermolecular forces The attractive forces between an instantaneous dipole and an induced dipole are called London dispersion forces after the physicist Fritz London. These forces are stronger for more polarizable species. Some molecules have a permanent dipole because of differences in electronegativities among the atoms. Such molecules experience dipole-dipole forces. All molecules experience dispersion forces and induced dipoles, and polar molecules also experience dipole-dipole forces. Chemistry 130 Energetics of solution: Intermolecular forces The intermolecular forces that we have seen London dispersion forces induced dipole interactions dipole-dipole interactions have a strong effect on the boiling points of liquids. Chemistry 130 Energetics of solution: Intermolecular forces Another type of intermolecular force is the hydrogen bonding interaction. Hydrogen bonding is an additional type of bonding interaction that requires a hydrogen atom on one molecule and a source of electron density on another molecule, usually a lone pair. Hydrogen bonding can be intramolecular as well as intermolecular. It can have a profound effect on the properties of a material when it is present. Chemistry 130 Energetics of solution: Hydrogen bonding Boiling points of covalent hydrides Chemistry 130 Energetics of solution: Hydrogen bonding The second-row hydrides NH 3, H 2O, and HF exhibit much higher boiling points that would be expected based on their molecular weights. Strong hydrogen bonding between the molecules is responsible for the large liquid phase range of these compounds.
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