chemistry.geometry-thermodynamics – Flashcards
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| Linear Geometry |
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| • All atoms lie in a straight line. • Bond angle: ?XAX = 180°. 180? g • Examples: diatomic species, HCN, CO2 |
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| Trigonal Planar(planar triangular |
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| • X atoms at the vertices (corners) of a triangle. • Each X atom is bonded to atom A located at the center of the triangle. • All four atoms are in a single plane. • Bond angle: ?XAX = 120°. • Examples: BF3, CO3 2 |
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| tetrahedral geometry |
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| • Four sided pyramid with triangular faces • X atom at each of the 4 vertices. • Each X atom is bonded to atom A located at the center of pyramid. • Bond angle: ?XAX = 109.5°. • First 3-dimensional geometry X • Examples: CH4, NH4 + |
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| trigonal bipyramidal geometry |
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| Planar triangular geometry (AX3) with one additional X atom above the plane and the other below the plane. • Each X atom is bonded to atom A located at the center of planar triangle. • Three Equatorial Bonds: Bonds between atom A and X atoms (Xeq) at the vertices of the triangle. • Two Axial Bonds: Bonds between atom A and X atoms (Xax) above/below the planar triangle. • Bond angles: • ?XeqAXeq = 120°. Xax eq eq 90? • ?XeqAXax = 90°. • ?XaxAXax = 180°. A X Xeq Xeq 120? 5 • Examples: PF5 |
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| octahedral geometry |
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| • Four X atoms at the vertices of a square, and atom A at the center of the square. • Four Equatorial Bonds: Bonds between atom A and X atoms (Xeq) at the vertices of the square. • One X atom above and another below the plane of the square. • Two Axial Bonds: Bonds between atom A and X atoms (Xax) above/below the plane of the square. • Bond Xax Xeq Xeq angles: • ?XeqAXeq = 90°. • ?XeqAXax = 90°. ?X AX 180° A X Xeq eq Xeq 90 ? • XaxAXax = 180°. • Examples: SF6 |
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| 3 types of valence electron repulsions? list in terms of repulsive force |
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| - lone pair--lone pair*strong -lone pair--bond pair*intermediate -bond pair--bond pair*weak |
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| region of high electron density (hed); identify individual regions of hed |
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| electron geometries -Each single, double, or triple bond is 1 region of hed. • each lone pair is 1 region of hed. • each unpaired electron (odd # of valence electrons) is 1 region of hed. 4) If more than arrangement of lone and bonding electron pairs is possible, select the arrangement which minimizes lone pair repulsions. • Trigonal bipyramidal: Place lone pairs in equatorial positions before axial positions. • Octahedral: Place the first lone pair in any one of the six equivalent regions of hed. Place the second lone pair opposite the first lone pair. 5) The molecular geometry (structure) is the arrangement of only atoms around the central atom, and is given in the following table. |
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| the most stable arrangement (fundamental geometry) associated with various numbers of regions of hed |
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| 2 Linear 3 Trigonal Planar 4 Tetrahedral 5 Trigonal Bipyramidal 6 Octahedral |
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| electronic geometry vs. molecular geometry |
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| molecular is only ATOMS around the central atom. |
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| dipole moment |
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| A measure of the polarity of a molecule Scheme #1 • Electron rich region has a partial negative charge (? -). • Electron poor region has a positive charge(x+ ). |
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| How to figure out if an atom is polar or nonpolar |
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| if dipole = 0, nonpolar molecule if dipole > 0, polar molecule -if all regions around the central atom are identical, the bond is nonpolar. -if regions of hed are non identical then the atom is polar. |
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| valence bond (vb) theory |
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| Theory of covalent bonding which describes a chemical bond as being formed by the overlap of: 1) Two atomic orbitals (s, p, d, f…), one from each atom of the bond. 2) Two hybrid orbitals. 3) An atomic orbital and a hybrid orbital. |
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| hybrid orbital |
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| Orbitals formed by the mathematical mixing of two or more atomic orbitals of a central atom. |
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| sigma bond |
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| A bond formed by the overlap of atomic or hybrid orbitals in which the shared electron density is concentrated directly along the internuclear axis between the two nuclei involved in bonding. • All single bonds are sigma bonds. |
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| pi bond |
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| A bond formed by the sideways overlap of a pair of unhybridized p orbitals, which concentrates electron density in two separate regions that lie on opposite sides of the internuclear axis between the two nuclei involved in bonding. |
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| a double bond in terms of sigma and pi bond |
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| 1 sigma and one pi bond |
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| a triple bond in terms of sigma and pi |
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| 1 sigma bond, 2 pi bonds |
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| single bond in terms of sigma and pi |
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| all single bonds are sigma |
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| mole |
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| base unit of amount of a chemical substance |
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| 6.022x10^23 |
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| 1 mol=? particles |
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| compound stoichiometry |
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| mole ratio of atoms within a compound |
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| reaction stoichiometry |
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| the mole ratio of compounds in a chemical reaction -Coefficients of a balanced chemical reaction supply the mole ratios by which reactants and products are related |
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| Reactants are consumed. • Products are formed. • There is a transfer of energy |
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| 3 things that happen in any chemical reaction: |
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| thermodynamics |
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| Study of the changes in energy and transfer of energy that accompany chemical and physical processes. |
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| energy(J)(kJ)(cal)(kcal) |
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| the capacity to do work 1 cal=4.184 J |
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| work(newtons*meter) |
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| force*distance |
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| heat(q) |
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| A measure of the internal energy that is absorbed or transferred from one body to another. |
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| heat measures internal energy absorbed or transfered from one body to the other, temperature is simply a measure of an objects hotness or coldness |
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| difference in heat and temperature |
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| internal energy (u) |
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| the total kinetic energy and potential energy of all the molecules of an object |
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| kinetic energy KE-1/mv^2 |
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| energy of motion equation=? |
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| potential energy |
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| energy possessed by an object due to its position or composition. -magnet, rubber band stretching |
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| 1) transferring energy only in the form of heat. 2) Transferring energy only in the form of work. 3) Transferring energy as a mixture of work and heat. |
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| (delta E) 3 ways to change the internal energy of a system |
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| First law of thermodynamics |
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| The total amount of energy in the universe is constant. OR…. • Energy can be converted from one form to another but cannot be created or destroyed. |
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| system |
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| substance under investigation chemical reaction happening inside the beaker |
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| surroundings |
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| rest of universe the beaker and outside the beaker |
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| universe |
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| system plus surroundings |
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| number of moles of each substance;physical state of each substance;temperature;pressure;volume |
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| 5 variables required to describe the thermodynamic state of a system |
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| state function |
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| A Property of a system that depends only on the state of the system, and not how the system came to be in that state. |
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| enthalpy |
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| cannot measure this but can measure change of it. a state function H=U+PV |
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| enthalpy change (delta H) |
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| The change in the heat content of a system that accompanies a process which occurs at a constant pressure. • Heat is commonly designated “q”… qp heat at a constant pressure. |
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| endothermic process |
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| system absorbs heat from surroundings |
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| exothermic process |
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| system releases heat to surroundings |
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| calorimetry |
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| Experimental technique used to measure the heat released or absorbed during a reaction. |
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| calorimeter |
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| device used to measure the heat released/absorbed during a reaction |
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| specific heat capacity |
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| amount of heat gained by calorimeter;aka calorimeter constant |
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| thermochemical reaction |
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| Chemical reaction and the corresponding ?H value. |
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| 1) CH3CO2H(aq) + NaOH(aq) ? NaCH3CO2(aq) + H2O(l) ?H = -56.8 kJ/mol 2) CH3CO2H(aq) + NaOH(aq) ? NaCH3CO2(aq) + H2O(l) + 56.8 kJ/mol |
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| 2 ways to write thermochemical reaction examples: |
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| Pressure=1 atm Temp=25 Celcius Delta H degrees |
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| what is the temperature,symbol, and pressure corresponding to standard conditions |
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| standard rate |
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| the most stable state of a substance at standard conditions i.e.H2O: most stable state at 1 atm and 25°C is H2O(l). • NaCl: most stable state at 1 atm and 25°C is NaCl(s). |
