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"Phase" Definition
any part of a system that is homogenous
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"Heat Capacity" Definition
a measure of the energy chance needed to change the temp of a substance --> think of it as internal energy capacity
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Heat Capacity Equation
- C: heat capacity
- q: heat
- T: temp
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"Specific Heat" Definition
simply the heat capacity per unit mass
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Specific Heat Equation
q = m c ΔT
- q: heat
- m: mass
- c: specific heat
- T: change in temp
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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- --> H2O
- we can solve for "q" in q=mcΔT and since @ const. P, q=ΔH, we have the heat of the rxn
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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)
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Phase Changes
- (1) Melting - Freezing
- (2) Vaporization - Condensation
- (3) Sublimation - Deposition
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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
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Boiling Point
Atmos. P = Vapour P. of a liquid
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Melting Point
Vapour Psolid = Vapour Pliquid
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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
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Identify where bonds are broken during phase changes
solid --> liquid (melting)
liquid --> gas (vaporization)
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Temp v. Energy Phase Change Graph
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Phase Change Diagram: triple pt, critical pt
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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
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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.
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What is the slope of a temp v. energy graph when the phase is not changing?
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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
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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
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Boiling Point Elevation Equation
ΔT = k bmi
- kb: a constant
- m: molality
- i: # of ions after dissociation
- (i.e. NaCl --> Na + Cl ∴i = 2)
- (i.e. MgCl2 --> Mg+2 + 2Cl ∴ i = 2)
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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
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Freezing Point Depression Equation
ΔT = k fmi
- kf: a constant
- m: molality
- i: # of ions after dissociation
- (i.e. NaCl --> Na + Cl ∴i = 2)
- (i.e. MgCl2 --> Mg+2 + 2Cl ∴ i = 2)
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Osmotic Pressure Concept
- only relevant when comparing one solution to another
- - think of a selectively permeable membrane
- if one side is concentrated, the water will move to wards that side in order to maintain the same dilution factor
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Osmotic Pressure Equation
Π = iMRT
- Π: osmotic pressure
- i: # of ions after dissociation
- M: molarity
- T: temp
- this gives you the pressure on one side of the membrane (the total pressure is the difference between both sides)
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