Chapter 5: Heat Capacity, Phase Change, & Colligative Properties Flashcards
Phase changes arise through what?
Other words, phase change results when, ….
Changes in which INTERNAL ENERGY is distributed over MOLECULES and SPACE
Energy of a molecule INCREASES ⬆️ or DECREASES ⬇️, or when SPACES is ENLARGED ↔️ or REDUCED ➡️⬅️
Phase changes are accomplished via ______ or ______.
Heat; work
Heat Capacity (C)
Added energy required to INCREASE the TEMPERATURE of the substance by 1 DEGREE.
C = q/
In ISOTHERMAL EXPANSION OF GAS, we can….
EXPAND a gas at CONSTANT TEMPERATURE by ADDING HEAT during expansion
2 Heat Capacities for a substance
- ) Constant VOLUME heat capacity (Cv)
2. ) Constant PRESSURE heat capacity (Cp)
1) VOLUME of system held CONSTANT, then…
2) PRESSURE held CONSTANT and substance allowed to expand, some of the energy can …
1) The system can do NO PV work; ALL energy change must be in form of HEAT (means: NONE of energy going in system can escape as work done by system)
2) Leave the system as PV work done on the surrounding as VOLUME CHANGES
At CONSTANT PRESSURE, a substance can do what to energy with
Absorb; Expel
Cp > Cv
A compound can ABSORB energy at what type of PRESSURE & VOLUME?
How does this happen?
Constant
By the stretching of its bonds
More energy a molecule has, …
The more energy it can channel into STRETCHING bonds (opposed to raising temperature)
Bond stretching can account for …
So for a compound with LOTS of bonds, the VALUE of Cp does what?
LARGE amount of energy ABSORPTION
Approaches the value of Cv
The ratio of heat capacity (Cp/Cv) it’s called…
Isentropic expansion factors
As a # of molecular bonds INCREASES,
Gamma APPROACHES 1
Greater Heat Capacity (C),
Greater ABSORBANCE w/o temperature change
Intermolecular forces of a solid or liquid are much STRONGER than those of a _____
Gas
Temperature will always INCREASE when energy is ADDED to a substance at CONSTANT _______ or _______.
Volume; Pressure
Temperature is ALWAYS increased when?
When ENERGY is ADDED to a substance at CONSTANT volume or pressure
Water has a specific heat of what?
1 calg-1(degree)C-1
cwater= 1calg-1(degree)C-1
What’s a CALORIMETER?
Device that measures energy change
A COFFEE CUP CALORIMETER is an example of what?
It’s an example of CONSTANT PRESSURE b/c it measures ENERGY CHANGE at atmospheric pressure
What is a BOMB CALORIMETER ?
It measures ENERGY CHANGE at CONSTANT VOLUME.
It tells the INTERNAL ENERGY CHANGE of a reaction
Heat is ______ change.
Enthalpy Change associated with MELTING is called?
Enthalpy Change associated with BOILING is called?
Enthalpy
Heat Fusion
Heat of Vaporization
Enthalpy change is a STATE CHANGE, therefore, the exact SAME Amount of HEAT absorbed during melting is released during ______.
Freezing
Different types of PHASE CHANGES:
Solid to Liquid = Melting
Liquid to Solid = Freezing
Liquid to Gas = Vaporization
Gas to Liquid = Condensation
Solid to Gas = Sublimation
Gas to Solid = Deposition
Entropy and Enthalpy signs for the phase changes:
Condensation: (+)
Vaporization: (+)
Sublimation: (+)
Freezing: (-)
Condensations: (-)
Deposition: (-)
When entropy and enthalpy both have the SAME SIGN, what does temperature dictate?
The DIRECTION of the process
(Ex: HIGHER temps push the process toward INCREASE IN ENTROPY and a DECREASE IN ENTHALPY
LOWER temps push the SAME process towards a DECREASE in ENTROPY and aN INCREASE IN ENTHALPY )
Phase changes at CONSTANT PRESSURE are governed by what?
Temperature
_________ and _______ are two INTENSIVE PROPERTIES that help determine what?
Pressure; temperature
Phase of a Substance
Phase diagram
Indicates phases of a substance at different PRESSURES AND TEMPERATURES
Triple Point
One point where a substance can exist in equilibrium as a SOLID, LIQUID, AND GAS
Heat fusion is…
The amount of heat that must be added to convert one mole of a substance COMPLETELY FROM A SOLID TO A LIQUID
When water is at BOILING POINT (100 C), when heat is ADDED, the added energy does not raise the temperature b/c:
The added energy is used to BREAK bonds b/n water molecules
At BOILING POINT, any added energy is used to break intermolecular bonds and NOT to INCREASE __________, so while the water is boiling, there is what?
Kinetic energy
- NO temperature increase
Heating a solid at CONSTANT temperature will do what?
MELT the solid
Colligative properties depend on what?
4 Colligative Properties of solutions:
Number of particles
- Vapor Pressure
- Boiling Point
- Freezing Point
- Osmotic Pressure
Addition of a nonvolatile solute will ______ the VP of solution in direct proportion to the number of particles added.
Lower
When does a substance boil?
When can the boiling point of a substance change?
When VP = local atmospheric pressure
By adding a solute
Addition of a Nonvolatile solute does what to VP and BP?
It LOWERS the VP and ELEVATES the BP
Van’t Hoff factor (i) has 2 values:
Expected value of ionic compound is …
- Expected 2. Observed
Number of ions created upon complete dissociation
What is ION PAIRING?
How does ion pairing come about?
Momentary aggregation of 2 or more ions into a SINGLE particle
Due to the STRONG attractions b/n (+) and (-) ions
Ion pairing INCREASES with _________ _________, and DECREASES with INCREASING ___________.
Solution concentration; temperature
Endothermic (breaking bonds) heat = _______ bonds, which leads to ______ _____, which you can predict a ______ _______.
Weak; high VP; low BP
Liquid solute, the impurities will ______ the MP
Lower
Mole fraction of solute ⬆️, then solvent will be the _______ preventing the solute from ________.
Impurity, freezing
Define OSMOTIC PRESSURE
A Measure of the tendency of WATER (or solvent) to move into a solution via OSMOSIS ( water that passes through a SEMIPERMEABLE membrane to a HIGH concentration)
Define Osmotic Potential
Partial measure of a systems free energy
Pure WATER is assigned an osmotic potential of 0
When a solute is ADDED, osmotic potential becomes ______.
At CONSTANT TEMPERATURE & PRESSURE, water flows from _____ osmotic potential to ______ osmotic potential.
Negative
Higher, Lower
