Module 3 Flashcards
Definition of internal energy
The energy that’s intrinsic to a material
State functions
Tells us the state of the system.
Does NOT depend (mathematically) on how we got from A to B, just uses the initial and final conditions.
Value is dependent only on the state the system is in, never on how that state was reached.
Path functions
(Mathematically) depends on how we got from A to B. Measures what happens in between the initial and final conditions.
Value is dependent on how the state of the system was reached.
First Law of Thermodynamics
The energy of the universe is constant.
The total change in energy of a system consists of the heat transferred to (delta H or q) and the work done (w) on a system.
If something releases heat, it is…
Exothermic
If something absorbs heat, it is…
Endothermic
Definition of specific heat capacity
The quantity of heat required to increase the temperature of one gram of a substance by one degree C/K
Is delta H (change in enthalpy) a state function or a path function?
State function. It uses only the initial and final conditions.
What does calorimetry measure?
Heat flow
Is enthalpy (H) a state function or a path function?
It’s a state function.
Note that enthalpy values can’t be measured directly. Only changes in enthalpy can be determined.
If delta H is negative…
…the rxn is exothermic, indicates that heat has been lost from the system.
If delta H is positive…
…the rxn is endothermic, indicates that heat has been gained in the system.
What does delta H predict?
Whether reactions will be endothermic or exothermic.
What does entropy predict?
Whether reactions will be spontaneous or not.`
Second Law of Thermodynamics
The entropy of the universe is increasing to a maximum.
What happens to entropy if the temperature of the system increases while volume remains constant?
Entropy increases, delta S is positive
What happens to entropy if the volume of the system increases while temperature remains constant?
Entropy increases, delta S is positive
What happens to entropy if both the temperature and the volume of a system increase?
Entropy increases, delta S is positive
What three properties do liquids have?
Viscosity (resistance to flow)
Surface tension
Vapor pressure
What would make a liquid more viscous?
Decreasing the temperature, decreasing the IMFs present
What would increase a liquid’s surface tension?
Strengthening the IMFs
What would increase a liquid’s vapor pressure?
Weakening the IMFs, increasing temperature
When at low temperatures is a rxn spontaneous?
At low temps, delta G is roughly equal to delta H.
Rxn must be edxothermic (delta H is negative) for it to be spontaneous.
When at high temperatures is a rxn spontaneous?
At high temps, delta G is roughly equal to -TdeltaS.
Rxn must increase in entropy (delta S is positive) for it to be spontaneous.
How does delta G predict spontenaity?
When delta G is negative, rxn is spontaneous.
When delta G is positive, rxn is NOT spontaneous, instead the reverse rxn is spontaneous.
When delta G = 0, the system is at equilibrium and neither the forwards nor reverse rxns are spontaneous.
Where does vapor pressure come from?
Particles at the surface of a liquid having enough kinetic energy so that they can escape the IMFs holding them in the liquid, vaporizing and entering the gas state above the liquid.
What would decrease a liquid’s boiling point?
Weakening the IMFs, lowering the external pressure
Breaking bonds is…
…endothermic.
Forming bonds is…
…exothermic.
When will a liquid boil?
When it’s vapor pressure is equal to the external pressure.
Why would a rxn be endothermic?
More bonds are created than broken.
More moles of stuff are created/present at the end of the rxn.
What is Gibbs Free Energy (G)?
Combines enthalpy and energy. Whether G is positive or negative allows us to predict a rxn’s spontenaity, and thus whether or not it will occur.
It also tells us how much of a particular type of work a thing/system can do.
How do we find at what temperature a rxn will become spontaneous, aka its crossover temp?
Set delta G = 0, then solve. When delta G = 0, the system is at equilibrium. It marks the crossover temp/point from spontaneous to non-spontaneous.
deltaG = 0 = deltaH - TdeltaS
Why is water a poor ideal gas?
Because it has a lot of IMFs holding it together, causing its collisions to be less than perfectly elastic.
Why do gases turn into liquids (condense) when the ideal gas law states that they shouldn’t?
IMFs
Which state of matter has more entropy: solid, liquid, or gas?
Gas
What are London Dispersion Forces and where do they come from?
LDFs are the weakest IMF. They exist in al matter and arise from the transient fluctuating dipole in each electron cloud inducing a similar dipole in neighboring electron clouds.
What kinds of IMFs are found in pure noble gas samples?
Only London Dispersion Forces
What would increase a molecule’s LDF?
Increasing surface area and mass
What are dipole-dipole interactions and where do they come from?
Occurs only in intrinsically polar molecules, molecules with a permanent dipole.
What would increase dipole-dipole IMFs?
Having a larger individual/intrinsic dipole, caused by a larger electronegativity difference in the molecule
What are hydrogen bonding IMFs and where do they come from?
Subset of dipole-dipole IMFs that arise because hydrogen is so small it can get really close to the next atom/molecule. Occurs only between hydrogen and either oxygen, nitrogen, or fluorine.
What are ion dipole IMFs and where do they come from?
Occurs when a molecule with an intrinsic dipole interacts with a dissolved ion, causing the molecules to orient themselves in certain ways
What would increase ion dipole IMFs?
Increasing the ionic charge of the dissolved ion
The heat of condensation describes…
…condensing. Gas to liquid.
The heat of vaporization describes…
…vaporizing. Liquid to gas.
The heat of crystallization describes…
…freezing. Liquid to solid.
The heat of fusion describes…
…melting. Solid to liquid.
What properties are solids dependent on?
Type of particle, the geometry of the particles in arrangement, and the forces holding the particles together
What are the four types of crystalline solids?
Ionic, metallic, covalent network, and molecular
What type of crystalline solid conducts electricity as a liquid but not as a solid, has a very high melting point, and is very brittle?
Ionic solid
What type of crystalline solid is good at conducting heat and electricity and is made out of electropositive elements?
Metallic solid
What type of crystalline solid is not conductive, has a very high melting point, and is very hard?
Covalent network solid
What type of crystalline solid is made of atoms from electronegative elements?
Covalent network solid
What type of crystalline solid is malleable and ductile and has a variable hardness and melting temp?
Metallic solid
What type of crystalline solid has a low melting point and is held together by IMFs?
Molecular solids
What type of crystalline solid is made of nonmetal element compounds, in building blocks of molecules, and is held together by IMFs?
Molecular solids
What is sublimation?
Phase change from solid to gas, without become a liquid in between
What is a triple point?
The temperature and pressure at which the three phases of a substance coexist in thermodynamic equilibrium.
What is a critical point?
The end point of a phase equilibrium curve, where phase boundaries vanish.
In the case of the liquid-vapor critical point, its the temp and pressure above which a substance exists as a supercritical fluid
Order the four IMFs from strongest to weakest.
Ion-dipole, hydrogen bonding, dipole-dipole, LDFs
What is deposition?
Phase change from a gas to a solid, without becoming a liquid in between.
In a unit cell, corner-centered atoms count as…
1/8
In a unit cell, face centered atoms count as…
1/2
In a unit cell, edge centered atoms count as…
1/4
In a unit cell, body centered atoms count as…
1
Which solid crystalline structure features separate bonding and inter-particle force interactions?
Molecular covalent solids
