# Chemistry Lect 5

 "Phase" Definition any part of a system that is homogenous "Heat Capacity" Definition a measure of the energy chance needed to change the temp of a substance --> think of it as internal energy capacity Heat Capacity Equation C: heat capacityq: heatT: temp "Specific Heat" Definition simply the heat capacity per unit mass Specific Heat Equation q = m c ΔT q: heatm: massc: specific heatT: change in temp Coffee Cup Calorimeter - measures the Δenergy at atmospheric pressure (∴ a constant pressure system)-used to measure heats of a reaction (@ constant pressure q=ΔH) i.e. we mix H+ + OH- --> H2Owe can solve for "q" in q=mcΔT and since @ const. P, q=ΔH, we have the heat of the rxn Bomb Calorimeter - measures Δenergy at constant volume- used to measure internal energy change (@ constant volume q=ΔU) i.e. use known heat capacity (C) of the container and the q=CΔT to deduce the internal energy (U) Phase Changes (1) Melting - Freezing(2) Vaporization - Condensation(3) Sublimation - Deposition When does evaporation occur? when the partial pressure above the liquid is less than (<) the vapour pressure of the liquid BUT atmospheric P. > vapour P. *this allows the liquid to evaporate rather than boil Boiling Point Atmos. P = Vapour P. of a liquid Melting Point Vapour Psolid = Vapour Pliquid Compare the amount of heat released when moving from liquid --> solid to the amount of heat absorbed when moving from a solid --> liquid Exactly the same amount of heat that is absorbed when melting is released when freezing Identify where bonds are broken during phase changes solid --> liquid (melting) liquid --> gas (vaporization) Temp v. Energy Phase Change Graph Phase Change Diagram: triple pt, critical pt Critical Point - critical temp: above which a substance cannot be liquified regardless of the pressure applied - critical pressure: required to produce liquification while the substance is at the critical temp critical pressure, critical temp = critical pt What happens to the temperature of a system during a phase change? When there is not a phase change? There is no change in temperature during a phase change. Otherwise, energy increases molecular movement which increases temperature. What is the slope of a temp v. energy graph when the phase is not changing? slope = 1 / mc m: massc: specific heat Colligative Properties - properties that depend only on the number of particles and not the type (1) vapour pressure(2) boiling point(3) freezing point(4) osmotic pressure Explain Boiling Point Elevation - with the addition of a nonvolatile solute there is a decrease in vapour pressure - boiling point occurs when V.P. = Atmos. P. - ∴ when V.P. decreases the b.p. increases Boiling Point Elevation Equation ΔT = kbmi kb: a constantm: molalityi: # of ions after dissociation (i.e. NaCl --> Na + Cl ∴i = 2)(i.e. MgCl2 --> Mg+2 + 2Cl ∴ i = 2) Explain Freezing Point Depression - the addition of a nonvolatile solute can interrupt the crystal lattice- this will lower the freezing point *be careful: eventually you get to a point where the solvent becomes the impurity preventing the solute from freezing --> ∴ the freezing point lowers at first and then rises again after it has hit this point Freezing Point Depression Equation ΔT = kfmi kf: a constantm: molalityi: # of ions after dissociation (i.e. NaCl --> Na + Cl ∴i = 2)(i.e. MgCl2 --> Mg+2 + 2Cl ∴ i = 2) Osmotic Pressure Concept - only relevant when comparing one solution to another - think of a selectively permeable membraneif one side is concentrated, the water will move to wards that side in order to maintain the same dilution factor Osmotic Pressure Equation Π = iMRT Π: osmotic pressurei: # of ions after dissociationM: molarity T: temp - this gives you the pressure on one side of the membrane (the total pressure is the difference between both sides) Authorlaskiru ID57072 Card SetChemistry Lect 5 DescriptionHeat Capacity, Phase Change, and Colligative Properties Updated2010-12-23T03:02:41Z Show Answers