Quiz 3 Flashcards
Potential Energy
Energy an object has by virtue of its placement in a field of force, like gravity
PE = ?
mgh
Kinetic Energy
Energy an object has by virtue of its motion
KE = ?
1/2mu^2 and 3/2RT
When KE is at max, PE is at _____
minimum
When PE is at max, KE is at _____
minimum
Internal (total) energy =
KE + PE
Types of molecular kinetic energy
Translation, rotation, vibration
Translation
Motion through space
Rotation
Motion about the center of mass
Vibration
Motion directed through chemical bonds
In a molecule, where is PE stored?
Bonds
Electrostatic
Intermolecular attractions - molecule interacts with neighboring molecules
Thermodynamics
Study of energy and its interconversion
How can energy be transferred?
As heat or work
Heat (q)
Net transfer of energy between objects due to temp gradient
Work (w)
Force (energy) acting over a change in h/d to move an object
ΔE =
q+w
What does E describe?
The state of the system
When does the state of a chemical system change?
When the system exchanges energy as heat or work
Surroundings
Everything around the system
First law of thermodynamics
The total energy of the universe is constant
What direction does energy flow?
High E concentration to low E concentration
Exothermic Process
Evolution of system that results in heat transfer to surroundings q<0 (heat lost)
Endothermic Process
Evolution of system that results in heat transfer to system q>0 (heat gained)
Expansion
Vf > Vi and ΔV > 0 and w < 0
Compression
Vf < Vi and ΔV < 0 and w > 0
Work done on system by surroundings =
+w
Work done on surroundings by system =
-w
Heat/work in
+q and +w
Heat/work out
-q and -w
Pressure-volume work (PV)
Expansion of a gas against a constant external pressure
State functions/variables
Describe the momentary condition of thermodynamic system or difference between two momentary conditions
Examples of state functions/variables
E, ΔE, T, P, V, n, KE, PE
Process/path funcitons
Describe the energy change associated with a particular process imposed on a thermodynamic system
Examples of process/path functions
q and w
Do state function depend on the path the system takes?
No
Increase in system temp =
Increase in system’s heat energy content
What happens if heat is added at constant volume?
T and P increase
Is there work when V is constant?
No
What is the heat flow measured under constant P conditions?
ΔH
Which R value do you use for molar heat capacity?
8.314
Molar heat capacity (ΔE) definition
Energy required to raise the temp of 1 mole of substance by 1K
What happens if heat is added at constant pressure?
T and V increase
What is the heat flow measured under constant V conditions?
ΔE
Molar heat capacity (ΔH) defintion
Enthalpy required to raise the temp of 1 mole of substance by 1K
Is work done at constant pressure?
Yes
Molar heat capacity definition
Energy required to raise the temp of 1 mole of a substance by 1K
How do we go from Cv to Cp?
Add 1R
For a polyatomic ion, are Cv and Cp greater than or less than Cv and Cp for a monatomic ion?
Greater
Is losing heat exothermic or endothermic
Exothermic
Isochoric
Constat Volume
Isobaric
Constant Pressure
Isothermal
Constant Temperature
When do we use the 101.3 J/L*atm conversion factor?
When going from L*atm to Joules
Hess’s Law
Going from one set of reactants to one set of products, overall change in enthalpy is the same (doesn’t depend on number of steps)
Can we measure absolute enthalpies
No
Calculate thermodynamics for compounds
Pure substance its normal phase at P = 1atm
Calculate thermodynamics for solutions
Concentration of 1M
Calculate thermodynamics for elements
The most stable form of the element at P = 1atm
What subscript is used for standard state
º
Standard enthalpy of formation (ΔHfº)
Enthalpy change that accompanies the formation of one mole of a compound from its elements with all substances in their stand states at 25ºC
Spontaneous Process
Will occur in a system left to itself; no action from the surroundings is necessary to drive the process
Non-spontaneous Process
Requires action from the surroundings to occur
Second Law of Thermodynamics
The entropy of the universe is always increasing
Are processes that lead to an increase in the entropy of the universe spontaneous or non-spontaneous
Spontaneous
Configuration
General arrangement of a system, which can be achieved by one or microstates
Microstate
Specific arrangement of a system corresponding to a particular configuration
Weight (omega)
Number of microstates associated with a given configuration
Entropy
Change in the arrangement of energy in response to a heat flow at a given temp
What does rev mean in qrev?
Reversible (q flows very slow)
ΔS (universe) > 0
Spontaneous
ΔS (universe) < 0
Spontaneous in opposite direction
ΔS (universe) = 0
At equilibrium
Third Law of Thermodynamics
The entropy of a perfect crystal at 0 K is 0
Standard Molar Entropy (S°)
Entropy change associated with heating one mole of a substance from 0 K to 298 K at 1 atm
Entropy in exothermic process
ΔS (surroundings) > 0
Entropy in endothermic process
ΔS (surroundings) < 0
Entropy from gas to liquid
ΔS (system) < 0, ΔH (system) < 0, ΔS (surroundings) > 0
Entropy from liquid to gas
ΔS (system) > 0, ΔH (system) > 0, ΔS (surroundings) < 0
Do gases contract or expand at low T?
Contract
Do gases contract or expand at high T?
Expand
ΔG<0
Spontaneous
ΔG>0
Spontaneous in opposite direction
ΔG=0
Equilibrium
When does the spontaneity of a rxn change?
After/before equilibrium
When are exothermic rxns with ΔS<0 spontaneous (-ΔH and -ΔS) ?
At low temps
When are exothermic rxns with ΔS>0 spontaneous (-ΔH and +ΔS) ?
At all temps
When are endothermic rxns with ΔS>0 spontaneous (+ΔH and +ΔS) ?
At high temps
What controls spontaneity when Tactual > X
ΔS
What is X?
Temp at which spontaneity changes
What controls spontaneity when Tactual < X
ΔH
Tactual = X
Equilibrium
Spontaneity when -ΔS and -ΔH
At low temps
Spontaneity when +ΔS and -ΔH
All temps
Spontaneity when +ΔS and +ΔH
High temps
Spontaneity when -ΔS and +ΔH
No temps (never spontaneous)
Standard Free Energy Change (ΔG°rxn)
Free energy change when reactants and products are in their standard state
Standard Free Energy of Formation (ΔG°f)
Free energy change that occurs in the formation of 1 mol of a substance in its standard state from elements in their standard state
If temperature is -Kelvin, what does that mean about the spontaneity?
Rxn is spontaneous at all temps
What is ΔG ?
Free energy change for rxns occurring at any temp or concentration
Whatis ΔG° ?
Change in free energy for a rxn involving compounds in their standard states
If ΔG° < 0 then _____
K > 1
If ΔG° = 0 then _____
K = 1
If ΔG° > 0 then _____
K < 1
