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Chemistry Midterm 2 Definitions.docx

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University of Toronto Mississauga
Judith C Poe

Study Notes for Chemistry Midterm 2 - Friday, Nov 9th Kinetic Molecular Theory  molecules are far apart; most of the volume is empty space  molecules are in constant motion; they travel in straight line paths  molecules exert no force on each other excepting during collisions  the average kinetic energy of the molecules depends on the temperature o (1) at constant volume V o as T ↑, velocity ↑ o as velocity ↑, there are more collisions between molecules and container so P↑ o therefore, P α T at constant V o (2) if V is variable o at T ↑, velocity ↑ and P ↑ o but as P ↑ the container expands until P↓ back to original P o therefore, P α 1/V at constant T, and v α T at constant P o (3) absolute T o since v α T, as T↓, v↓ o when v = 0, ½mv = 0 o a temperature below this point would have no physical meaning (absolute zero) Diffusion and Effusion  Diffusion → process by which a gas mixed with another; random movement of gas particles in a medium  Effusion → process by which a gas escapes a container through a small opening; gas movement through a hole  Molecular Velocities o at constant T, the average kinetic energy and velocity are constant o there is a wide range of values for the kinetic energy and velocity of individual molecules o relative average velocities depend on relative masses  Graham's Law: ½m v = ½m v at constant T 1 1 2 2 v1= √m 2 v m 2 1 So, the heavier the molecule, the slower it moves. Diffusion and effusion rates are known as r, so: r1= √M 2 r2 M 1 Mean Free Path: the average distance a particle travels before it collides with other particles effusion < diffusion < molecular velocities (due to collisions) Van Der Waal's Equation: 2 2 (P + n a/V )(V-nb) = nRT where, P = pressure n = moles a = constant, measure of strength of the intermolecular forces between molecules V = volume n /V = concentration 2 b = excluded volume/mol (P + n a/V ) is an adjustment to the Pressure of the container, because the attraction between the molecules is not negligible, especially if the container is so small (V-nb) is also another adjustment but to the Volume of the container, because molecules take up space, and if the container is small, the space the molecules occupy will not be negligible *The lower the Van Der Waal's constants, the lower (colder) the boiling point ρ = MP/RT (molar mass x pressure/r x temperature) Compressibility Coefficient:  z = PV/RT  z should be equal to 1 if gases behave ideally  the extent to which z deviates from 1 is a measure of how non-ideal the behaviour is  for every gas, at some temperature it will behave ideally  this is called the Boyle Temperature  based on chemical composition and Van Der Waal's numbers Coulomb's Law F α q1q2/r2 F = kq1q2/r2 F = q1q2/4πϵ r 2 o Define Equilibrium  Equilibrium constant (Kc) is the ratio of forward and backward rate constants  The larger the equilibrium constant, the more product is formed  Kc is the equilibrium constant, Kp is the equilibrium constant in respect to pressure  Kp = Kc(RT) Δn gas Le Chatelier's Principle Change Result Increase in reactants (R↑) Shift right → so products ↑ to maintain K Decrease in reactants (R↓) Shift left ← so products ↓ to maintain K Increase temperature, exothermic (T↑) Shift left ← so reactants ↑ so T↓ and K↓ (R ↔ P + heat energy) Increase temperature, endothermic (T↑) Shift right → so products ↑ so T↓ and K↑ (R + heat energy ↔ P) Increase in volume (V↑), decrease in pressure Shift to the side of the reaction that has MORE (P↓) of reactants (gases only) moles Decrease in volume (V↓), increase in pressure Shift to the side of the reaction that has (P↑) of reac
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