# Chemistry Lect 5

The flashcards below were created by user laskiru on FreezingBlue Flashcards.

1. "Phase" Definition
any part of a system that is homogenous
2. "Heat Capacity" Definition
a measure of the energy chance needed to change the temp of a substance --> think of it as internal energy capacity

3. Heat Capacity Equation

• C: heat capacity
• q: heat
• T: temp
4. "Specific Heat" Definition
simply the heat capacity per unit mass
5. Specific Heat Equation
q = m c ΔT

• q: heat
• m: mass
• c: specific heat
• T: change in temp
6. 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
7. 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)
8. Phase Changes
• (1) Melting - Freezing
• (2) Vaporization - Condensation
• (3) Sublimation - Deposition
9. 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
10. Boiling Point
Atmos. P = Vapour P. of a liquid
11. Melting Point
Vapour Psolid = Vapour Pliquid
12. 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
13. Identify where bonds are broken during phase changes
solid --> liquid (melting)

liquid --> gas (vaporization)
14. Temp v. Energy Phase Change Graph
15. Phase Change Diagram: triple pt, critical pt
16. 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
17. 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.
18. What is the slope of a temp v. energy graph when the phase is not changing?
slope = 1 / mc

• m: mass
• c: specific heat
19. 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
20. 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
21. Boiling Point Elevation Equation
ΔT = kbmi

• 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)
22. 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
23. Freezing Point Depression Equation
ΔT = kfmi

• 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)
24. 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
25. 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)
 Author: laskiru ID: 57072 Card Set: Chemistry Lect 5 Updated: 2010-12-23 03:02:41 Tags: Chem Heat Phase Colligative Folders: Description: Heat Capacity, Phase Change, and Colligative Properties Show Answers: