Study Guide #3
Study Guide #3 CHMY 141N - 00
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This 15 page Study Guide was uploaded by Corymarie Notetaker on Sunday November 1, 2015. The Study Guide belongs to CHMY 141N - 00 at University of Montana taught by Mark Cracolice (P) in Fall 2015. Since its upload, it has received 46 views. For similar materials see College Chemistry I in Chemistry at University of Montana.
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Date Created: 11/01/15
CHMY 141 Study Guide Exam 3 Lessons 18-26 Lesson 17 What Models Represent the Gaseous State? (review chapter) ● Boyle’s Law: volume is inversely proportional to pressure ● Charles’s Law: volume of a gas is directly proportional to Kelvin temperature PV=nRT ● Avogadro’s Law: gas volume is directly proportional to the amount of gas in a container ● Ideal Gas Law: PV=nRT (ideal gas equation) where R is the proportionality constant in the ideal gas equation and its units; L*atm/mol*K. ● Macroscopic Properties that Characterize Gases; ○ Gases may be compressed: a fixed quantity of air may be made to occupy a smaller volume by applying pressure ○ Gases may be expanded: a small volume of gas can expand to occupy a larger volume uniformly ○ Gases have low densities ○ Gases may be mixed in a fixed volume ○ Gases exert constant pressure on the walls of its container uniformly in all directions ● Particulate-Level of Gas Properties; kinetic molecular theory: describes an ideal gas model by which we can visualize the nature of the gas by comparing it with a physical system we can either see or readily imagine. ○ Gases consist of particles moving at any given instant in a straight line: explains why gases fill their containers. When a particle strikes a container wall, it exerts a force at the point of collision, suggesting an explanation to gas pressure. ○ Molecules collide with each other and with the container walls without loss of total kinetic energy: If gas particles lose energy as a result of their collisions the combined forces would become smaller, and the pressure would gradually decrease. Also, temperature would decrease due to their lack of motion and would eventually become a liquid. Since these don’t happen we can conclude that energy is not lost in molecular collisions ○ Gas molecules are widely spaced: otherwise the densities of gases would not be as low as they are ○ The actual volume of molecules is negligible compared to the space they occupy ○ Gas molecules behave as independent particles; attractive forces between them are negligible: the large distances between gas particles ensures that attractions between molecules are negligible ● Real gases approach ideal gas behavior closely at low pressures and high temperatures. Otherwise two features need to be reconsidered; ○ The space available for each molecule to move about is not the total volume of its container; it is the container volume minus the actual volume occupied by all other molecules in the sample ○ Molecules are attracted to each other. Theses attractions are at a minimum when the molecules are widely separated. However, when the molecules are close to each other, the attractions are strong enough to affect the behavior of their near neighbors and the pressure they exert when colliding with the container walls Lesson 18 How are Measurable Quantities Related in a Chemical Change when One or More Species is a Gas? ● Density of a gas= m/V=(MM)P/RT ● Molar Volume of a gas= V/n=RT/P ○ The molar volume (MV) of a gas is the volume occupied by one mole of gas molecules. The molecules may all be the same, or they may be a mixture of two or more gases. ○ All gases have the same molar volume at any given temperature and pressure ○ Molar volume is pressure and temperature dependent ● In a gas stoichiometry problem, either the given quantity or the wanted quantity is a gas at specified temperature and pressure. The problem is usually solved in two steps, the order of which depends on whether the gas volume is the wanted or the given quantity. ● Avogadro’s Law states that gas volume is directly proportional to number of moles at constant temperature and pressure. This means that the ratio of volumes of gases in a reaction is the same as the ratio of moles, provided that the gas volumes are measured at the same temperature and pressure. The coefficients give us a ratio of gas volumes as well as a ratio of moles. (helpful for conversions in stoichiometry) ● Often the given and wanted gas volumes are at different temperatures and pressures. You can use the combined gas equation to solve for2V to change from given conditions to wanted conditions. Then both gases are at the same temperature and pressure, and you can use the volumes given to get volume wanted proportionality, using coefficients ○ V2=V 1(P1/2 )*2T1/T ) Lesson 20 How is Energy Related to Chemical Systems and Chemical Change? ● Energy is the ability to do work or to transfer heat. ● he work(w) done to move an object is the product of the magnitude of the force(f) and the distance(d) it is moved. w=f*d ● Heat is the form in which energy is transferred between substances with different temperatures. ● Temperature is a measure of the average energy of the particles in a substance. ● Exothermic Reaction: a chemical change that releases energy to its surroundings ○ energy is a product in the chemical equation ○ ex: something burning releases energy in the form of heat, that you can feel ● Endothermic Reaction: a chemical change that absorbs energy from its surroundings ○ energy is a reactant in the chemical equation ● Potential Energy: The potential energy of an object depends on its position in a field where forces of attraction and/or repulsion are present ○ oppositely charged particles have greater potential energy when they are far apart and low when they are close. Same charged particles have greater potential energy when they are close, and low when they are far apart. ○ Chemical energy comes largely from the rearrangement of charged particles in an electrostatic field ● Kinetic Energy: energy of any moving object ● joule is defined as 1 kg*m /s ● 1 calorie(cal)= 4.184 joules ● 1 kilocalorie= 1000 calories= 1 Calorie(Cal) ● A thermodynamic system is the portion of the universe under consideration, the rest is called the surroundings ● State function: is a property whose value is determined only by the state of a system at any given moment. ● Internal Energy: is the energy of a system that results from sources other than the influence of external forces. ● First Law of Thermodynamics; the internal energy of a system changes by an amount equal to the sum of the heat that flows into or out of the system and the work done by or on the system. △E=q+w ○ △E is the change in internal energy of the system, q is the heat flow, w is work done ○ internal energy of a system, E, is a state function. Heat flow, q, is not a state function Lesson 20 How is Energy Related to Chemical Systems and Chemical Change? ● Enthalpy,H: is the heat content of a system.E is internal energy, P pressure, V volume ● Heat of Reaction/Enthalpy of reaction, △H, is the heat given off or absorbed in a reaction. ● Thermochemical equation:an equation that includes a change in energy. Must include state symbols for each element or formula. ○ Two ways to write it ■ include the △H in the chemical equation as it is a product or reactant, depending on the type of chemical change ■ △H written to right of the chemical equation, indicating if it is negative or positive (exothermic reaction is negative, endothermic reaction is positive) ● Thermal stoichiometry: The proportional relationships between moles of different substances in a chemical equation, expressed by their coefficients, extend to energy terms. Lesson 21 What are the Relationships Among Heat Energy, Temperature, and Mass for a Pure Substance ● Enthalpy of vaporization, △H : the amount of energy it requires to vaporize a substance at its boiling point, q, per an amount vap of of the substance, m. △H vap= q/m express all heats of vaporization in kJ/g ○ at the particulate level, we can think of heat of vaporization as being the energy needed to overcome the attractive forces among the particles of a liquid, causing the energy of the particles to become sufficiently high so that their motion prevails over the attractions. ● Enthalpy/Heat of condensation: when a vapor condenses to a liquid at its boiling point. Values are negative, indicating that energy is removed(exothermic). Opposite of enthalpy of vaporization ○ calculations with energy required for boiling or condensing is finding the energy added or removed in changing the state of a given amount of material. Use the equation; q=mX△vap ● Enthalpy of fusion, △H : the energy required to melt one gram of a substance, usually expressed in Joules/gram fus ● Heat of solidification: the amount of energy released in freezing a sample, equal to heat of fusion, but the sign is negative ○ formulas are just like △H vap ● change in temperature: △T= Tfinal initiaf- i ● Heat flow, q, in heating or cooling a substance is proportional to both the mass of the sample, m, and its temperature change, △T. The proportionality constant, c, is a property of a pure substance called its specific heat. ○ Specific heat is the heat flow required to change the temperature of one gram of a substance by one degree Celsius. Substance with high specific heat is best for retaining energy (values in data pack) ○ c= q/mX△T Lesson 21 What are the Relationships Among Heat Energy, Temperature, and Mass for a Pure Substance Procedure How to Calculate Total Heat Flow for a Change in Temperature Plus a Change of State Step 1 Sketch a graph having the shape shown in figure 21.1. Mark the starting and ending points for the particular problem. Then mark the beginning and ending points of any change of state between the starting and ending points for the problem Step 2 Calculate the heat flow, q, for each sloped and horizontal portion of the graph between the starting and ending points Step 3 Add the heat flows calculated in step 2. Caution: be sure the units are the same, either kilojoules or joules, for all numbers being added ❖ Slopedareasofgraphs:q=mXcX△T ❖ Horizontalareasofgraphs:qfus/vap ➢ fuswhensolidmeltsorliquidfreezes ➢ vapwhenliquidvaporizesorgascondenses Lesson 22 How are Heat Energy Changes Determined? ● Calorimetry: type of experimental process, where heat transfer is used to determine specific heat or heat of reaction ● Calorimeter: is an isolated segment of the universe-a system-that can neither transfer heat from nor transfer heat to the surroundings ● Calorimetry is based on the Law of Conservation of Energy: the sum of the heat transfers must equal zero ○ when heat is transferred into or out of a substance, it can be calculated by; q=mXcX△T ○ calorimeter constant, K K =q/△T cal cal ● bomb calorimeter/combustion calorimeter: most common device used to measure the heat of reaction of compounds that burn in an oxygen atmosphere, the heat of combustion ○ in a coffee-cup calorimeter, the pressure remains constant and thus the heat transferred, q, is equal to the change in enthalpy, △H. In a bomb calorimeter, the gaseous products of combustion cause a change of pressure. For a bomb calorimeter- △H=q+△(PV) ● △H is the final amount of heat energy, or enthalpy, in a system minus the initial amount. △H for a reaction is the heat content of the products of that reaction minus the heat content of the reactants ● Enthalpy (or heat) of formation,f△H°, is the change in enthalpy for the reaction in which pure, stable elements react, at a pressure of 1 bar if they are gaseous, to form one mole of product, also at 1 bar if it is a gas ○ the requirement that a heat of formation equation must have one mole of product often makes it necessary to use fractional coefficients for the reactant elements ● △H° for a reaction may be calculated by applying this relationship, △H°= ∑(nX△H° )products - △H°= ∑(nX△H° )reactants,to the chemical f f equation of the reaction ○ n is the number of moles of that species(coefficientsf and H° is the standard enthalpy of formation of that species, which may be found in the Selected Thermodynamics Values Table in the Appendix. The product of these two numbers is the contribution that species makes to the standard enthalpy of that reaction, H° ● Enthalpy is a thermochemical property of every substance, it is a state function ● Enthalpy of combustion is the △H° when one mole of a substance is burned in an excess of oxygen ○ △H° fan be determined by algebraic manipulation of thermochemical equations for which △H° values are known Lesson 22 How are Heat Energy Changes Determined? 2B 3A 4A 5A 6A 7A 8A H2 (g) He (g) C (s- N 2(g) O2 (g) Ne (g) graphi)e F2 (g) P 4(s) S8(g) Cl2(g) Ar (g) Kr (g) All others are solid Br2 (l) 2 (s) Xe (g) Hg (l) Rn (g) Lesson 23 How are Electrons Distributed Within an Atom? The Bohr Model ● electromagnetic radiation: visible light, radio, television and microwave waves are some variations of this type of energy ○ a form of energy that consists of both electric and magnetic fields ■ travels at the speed of light: 3.00x10 m/s (symbol c) ● continuous spectrum: white light ● Line spectrum: elements display discrete lines of color, when separated through a prism, that indicate that they are individually distinct ● Planck: energy of the electrons in the atoms of the material is directly proportional to their frequency; E∝ν ● Photon: presented by Albert Einstein, energy is released in “packets” of electromagnetic radiation. A photon is a particle of light ● wave-particle duality: particles have wavelike and particle-like properties ● Hz=1/s=1 s (unit for frequency of a wave) ● Maxwell discovered that electromagnetic radiation trave-34through space at a fixed speed so; c=λxν (speed of light = wavelength x velocity) ● energy of electrons; E=hν (E-energy, h-Planck’s constant 6.626x10 J*s, ν-velocity) ○ Planck’s quantum concept tells us that light is not a continuous flow of radiation, but rather a series of individual photons ● photoelectric effect: experiment to confirm photons. Light can cause the ejection of electrons, the photoelectric effect depends on the frequency of the light shined on the metal surface ○ energy of a photon= (energy needed to eject electron) + (Kinetic energy of electron after ejection) ● Bohr reasoned: ○ Quantized: an amount that is limited to specific values ○ Continuous: is an infinite number of other acceptable values ■ a line spectrum is quantized, but the spectrum of white light is continuous ○ Quantized energy levels: at any instant, the electron may have one of several possible energies, but at no time may it have an energy between them ■ quantum leap/jump- process by which an electron moves between orbits ■ ground state- the condition when all electrons in an atom occupy the lowest possible energy levels ■ excited state- when an atom absorbs energy and the electron moves to a higher level ○ E= -R x1/n R -Rydberg constant 2.1798x10 J, E-electron energy levels H H Lesson 24 How are Electrons Distributed Within an Atom? The Quantum Mechanical Model ● de Broglie proposed that all particles have a wavelength when in motion; λ= h/mν λ-wavelength, h-Planck’s constant, m-mass, ν-velocity ○ electrons travel as waves ● Heisenberg Uncertainty Principle: (△x)(m△ν)≥h/4π△x-uncertainty in position, △ν-uncertainty in velocity ○ the smaller the uncertainty in one quantity, the greater the uncertainty in the other ● Quantum mechanical model of the atom: Schrӧdinger applied the principles of wave mechanics to electron in an atom ○ Schrӧdinger wave equation ■ wave function of the electron is the unknown that the equation is solved for. It is the mathematical description of the wave ■ the square of the wave function is the probability density of the electron, the probability of finding the electron in a region of space ■ yields four quantum numbers that are used to identify electron in a multi-electron atom ● Quantum Numbers: ○ Principal energy level; represented by n. Energies increase as the number increases ○ Sublevel; ℓ= (n-1). s, p, d, f, levels increasing as such ○ Orbital; probability densities. mℓ= -ℓ,..., 0,..., +ℓ (figure 24.3 should be memorized for the shapes of s, p and d orbitals) ○ number of electrons; Pauli exclusion principle- limits the population of any orbital to two electrons Sublevel Letter Quantum Designatio Lesson 24 How are Electrons Number n Distributed Within an Atom? ℓ The Quantum Mechanical Model ℓ n Number of Sublevels Identification of Sublevels ℓ 1 1 1s ℓ 2 2 2s, 2p 3 3 3s, 3p, 3d Sublevel Orbital Maximum Electrons per s Sublevel 4 4 4s, 4p, 4d, 4f 5 5 5s, 5p, 5d, 5f, [5g] 6 6 6s, 6p, 6d, [6f,6g, 6h] 7 7 7s, [7p, 7d, 7f, 7g, 7h, 7f] Lesson 25 How are Electrons Distributed Among Orbitals Within an Atom? ● Electron configuration: the ground-state distribution of electrons among the orbitals of a gaseous atom. Two rules guide the assignments of electrons to orbitals: ○ at ground state the electrons fill the lowest energy orbitals available ○ no orbital can have more than two electrons ● The periodic table is a guide to the order of increasing sublevel energy ○ mentally divide the periodic table into four blocks: ■ s-block: Groups 1A and 2A [period 1 in the s block corresponds to n=1] ■ p-block: Groups 3A through 8A [period 2, 3, 4,... in the s and p blocks correspond to n= 2, 3, 4, …] ■ d-block: the B Groups [begins with n=3] ■ f-block: lanthanides and the actinides [begins with n=4, 4f are lanthanides and 5f are actinides] ● Using the periodic table as a guide, electron configurations can be written for elements. 1 2 2 6 1 ○ ex: H= 1s Na= 1s 2s 2p 3s ● Instead of writing long electron configurations a noble gas core is used, replacing the long electron configuration “middle” of an element 1 ○ ex: Na= [Ne]3s ● Interruptions appear at chromium Cr= [Ar]4s 3d and copper Cu= [Ar]4s 3d ● Orbital diagram: a diagram that shows how many electrons are in each orbital ○ you show the location of each electron by drawing boxes representing orbitals. An orbital occupied by one electron is indicated by drawing in the box a half arrow pointing up. Two electrons is shown by two half arrows, one pointing up and one down. When there is more that one orbital for a given ℓ value, you put the electrons in the boxes one at a time at first, then add additional electrons to the orbitals, doubling up if necessary ● Hund’s rule: the most stable arrangement of electrons in a sublevel is the one that has the maximum number of unpaired electrons ○ the normal practice is to use noble gas cores with orbital diagrams to allow focus on the orbitals that are half-filled or empty ● valence electrons: related to the total number of s and p electrons in the highest occupied energy level ○ Group 1A element have ns of the highest occupied principal energy level, all have one valence electron 2 3 ○ Group 5A have the general configuration of ns np , all have five valence electrons ○ Notice that for every group the number of valence electrons is the same as the group number ● Another way to show valence electrons uses Lewis’s symbols, which are also called electron dot symbols Lesson 25 How are Electrons Distributed Among Orbitals Within an Atom? Group 1A 2A 3A 4A 5A 6A 7A 8A s electrons 1 2 p 1 2 3 4 5 6 electrons 1 2 1 2 3 4 5 6 Electron ns ns np np np np np np configuration Group 3B 4B 5B 6B 7B ← 8B → 1B 2B d electrons 1 2 3 5 5 6 7 8 10 10 Electron 3d1 3d2 3d3 3d5 3d5 3d6 3d7 3d8 3d10 3d10 configuration Lesson 26 What Causes Periodic Trends in Properties of Elements? ● Effective nuclear charge, Z : the charge experienced by an electron in a many-electron atom. eff ○ can be estimated by subtracting the number of electrons in the noble gas core of an atom from the total number of electrons in the atom ● Atom Sizes ○ There are two primary influences on the size of atoms: highest occupied principal energy level and effective nuclear charge ○ moving down the periodic table, n, so atomic size generally increases from top to bottom on the periodic table ○ moving across a period, principal energy level remains the same, but effective nuclear charge increases, thus decreasing atomic size from left to right across the periodic table ● Size of Ions ○ cation ion always significantly smaller than its parent atom ○ anions are always significantly larger than their parent atoms ○ isoelectronic means same number of electrons ● Ionization Energy: the energy required to remove one electron from a gaseous atom of an element ○ ionization energy generally decreases from top to bottom on the periodic table ○ increases from left to right on the periodic table ○ Second ionization energy; always higher than the first ionization energy ● Electron affinity: the change in the energy that occurs when an electron is added to a gaseous atom or ion ○ increasingly greater change in energy from left to right ○ adding an electron to an atom is an exothermic process and becomes more exothermic from left to right across the periodic table ○ no significant periodic trend top to bottom on the periodic table ● Metal: an element that has a tendency to lose electrons in reaction and form a positive ion ○ stair-step line on the periodic table separates metals from nonmetals ○ elements at the division are called metalloids; B, Si, As, Te, At, Ge, Sb 1 ● Alkali Metals: Group 1A elements. All hav2 ns valence electron configuration. Form 1+ ion ● Alkaline Earths: Group 2A elements. All have ns valence electron configuration. Form 2+ ion ● Halogens: Group 7A elements. All have a ns np valence electron configuration. Form 1- ion 2 6 ● Noble Gases1Group 8A elements. All have ns np valence electron configuration. Are not reactive ● Hydrogen: 1s configuration. Has properties of alkali metal and halogen families, however doesn’t fit with any chemical family so, must be considered by itself
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