Thermodynamics Flashcards
What is thermodynamics?
The science of the relationship between heat + other forms of energy
What is thermochemistry?
The study of quantity of heat absorbed or evolved by chemical reactions
What is energy?
The capacity to do work
What are the different types of energy?
Radiant energy Thermal energy Chemical energy Nuclear energy Potential energy
What is kinetic energy?
The energy of motion
What is potential energy?
Stored energy
What is thermal energy?
Kinetic energy of molecular motion, measured by finding the temperature of an object
What is heat?
The amount of thermal energy transferred from one object to another as a result of temperature difference between the two
What is the law of conservation of energy?
Energy cannot be created or destroyed
What is the 1st law of thermodynamics?
Energy cannot be created or destroyed
What can isolated systems not do?
Neither do work upon nor heat their surroundings
Because isolated systems cannot do work or heat their surroundings what does it mean?
Internal energy of isolated systems remain constant
How do you calculate energy?
ΔE =E final - E initial
What is an exothermic process?
A release of heat corresponding to a decrease in enthalpy
What is an endothermic process?
An input of heat that corresponds to an increase in enthalpy
What is an open system?
Can exchange both matter + energy with the surroundings
What is a closed system?
Can exchange only energy with surroundings
What is an isolated system?
Can exchange neither energy nor matter with its surroundings
What is a state function?
Use to quantify the heat foe into or out of a system under constant pressure
How do you calculate work?
Force X Distance
What is expansion work?
Work done as a result of a volume change in the system
What is enthalpy?
A state function whose value depends on the current state of the system, not the path taken to arrive at that state
What is the equation if the vol is constant?
qv = ΔE
What is the equation if pressure is constant?
qp = ΔE + PΔV
What is the equation for enthalpy change?
ΔH = products - reactants
What is thermodynamic standard state?
Most stable form of a substance at 1 atm pressure + at 25 degrees at 1M conc
What is the equation for work?
Work = -PΔV
How do you calculate work?
Calculate vol = final - initial
Calculate pressure = X atm
Put into equation
Then cancel out units to give J
What is enthalpy of fusion?
The amount of heat necessary to melt a substance without changing its temp
What is enthalpy of vaporisation?
The amount of heat required to vaporise a substance without changing its temp
What is enthalpy of sublimation?
The amount of heat required to convert a substance from a solid to a gas without going through a liquid phase
What is H2O (s) —-> H2O (l)?
Endothermic
= +ΔH
What is H2O (l) —-> H2O (s)?
Exothermic
= -ΔH
How do you calculate ΔE?
ΔE = ΔH - PΔV
What is calorimetry?
Measure of heat flow at constant pressure
What is differential scanning calorimetry?
Measures difference in heat transferred to + from sample in comparison to reference material
What is heat capacity?
The amount of heat required to raise the temp of an object by a given amount
What is the equation for heat capacity?
q = C X ΔT
What is molar heat capacity?
The amount of heat required to raise the temperature of 1 mol of a substance by 1 degree
What is the equation for molar heat capacity?
q = Cm X moles of substance X ΔT
What is specific heat?
The amount of heat required to raise the temp of 1g of a substance by 1 degree?
What is the equation for specific heat?
q = specific heat X mass of substance X ΔT
What is Hess’s Law?
The overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for individual steps in the reaction
What is the equation for the Haber process?
3H2 (g) + N2 (g) —-> 2NH3 (g)
What is the standard enthalpy of formation?
Heat change when 1 mole of a compound is formed from its elements at a pressure of 1 atm
How do you calculate ΔH for standard enthalpy of formation?
Products - reactants
What is standard heat of formation?
Enthalpy change of formation of 1 mol of a substance in its standard state from its constituent elements in their standard state
What are the steps for calculating standard enthalpy of formation?
Write enthalpy of formation reaction
Add given rxns so that it gives desired rxn
What is bond breaking?
Endothermic
What is bond making?
Exothermic
What is bond dissociation energy?
Amount of energy that must be supplied to break chemical bond in an isolated molecule in gaseous state + so amount of energy released when bond forms
What do exact values depend on?
Bond order + electronic environment of 2 atoms compromising the bond
How do you calculate bond enthalpies?
Reactants - products
What does it mean if the more oxidised a fuel is?
Less energy we can get from its combustion
What is a spontaneous process?
A process that, once started, proceeds on its own without a continuous external influence
When will a spontaneous reaction occur slowly?
If it has a high Ea
What is entropy?
The amount of molecular randomness in a system
When are spontaneous processes favoured?
Decrease in H (-ΔH)
Increase in S (+ΔS)
What is the equation for ΔS?
S final - S initial
What happens to entropy as order increases?
Decreases
What happens to entropy as disorder increases?
Increases
Describe entropy of solid, liquid + gas
Solid < liquid < gas
What is entropy?
Is the measure of how dispersed energy + matter is
What is change in entropy equal to?
The heat transferred reversibly to it, divided by the temp at which the transfer takes place
Is entropy a state function?
YES
What is the 2nd Law of Thermodynamics got to do with?
Entropy
Why is entropy reversible?
Equal temp at either side of thermally conducting walls
Why is entropy heat?
Because its random molecular motion
Work = ordered molecular motion
Why does entropy got to do with temperature?
Accounts for randomness of molecular motion
When is a given entropy change most significant?
For cold system
How do you calculate entropy of heating H2O?
ΔS = q rev/T
How do you calculate ΔS accompanying heating?
ΔS =C In (Tf/Ti)
C = heat capacity of system
Ti = initial temp
Tf = final temp
What does it mean when Tf > Ti?
Log is positive = ΔS > 0 = what we would expect
When are entropy changes higher?
Things with high heat capacities
What are phase transitions accompanied by?
Entropy changes
Why does entropy increase in phase transitions?
Molecules are able to move more freely upon melting or boiling = increase entropy
How do you calculate entropy of vaporisation of H2O?
ΔS1 = C p,m(H2O, L)In(Tf/Ti)
ΔS2 = ΔvapH(Tb)/Tb
ΔS3 = C p,m(H2O, g)In(Tf/Ti)
ΔS1 + ΔS2 + ΔS3
What is C p,m?
Molar heat capacity at constant pressure
What is 2nd Law of Thermodynamics?
The amount of heat passing to/from the surroundings is equal + opposite to the heat leaving/entering the system
How do you calculate entropy of surroundings?
ΔS sur = -ΔH/T
What is the main 2nd Law of Thermodynamics?
The entropy of the universe increases in spontaneous process + remains unchanged in an eqm process
What is the 3rd Law of Thermodynamics?
The entropy of a perfectly ordered crystalline substance at 0K is zero
What happens at a higher temp?
Greater molecular motion
Broader distribution of individual molecular energies
More randomness
Higher entropy
What happens at lower temp?
Less molecular motion
Narrower distribution of individual molecular energies
Less randomness
Lower entropy
What are absolute entropies equal to?
Absolute zero
What is standard molar entropy?
The entropy of 1 mole of a pure substance at 1 atm pressure + specified temp
What is the standard entropy of reaction?
The entropy change for a reaction carried at 1 atm + 25 degrees
When do processes occur spontaneously?
If overall entropy of universe increases
How do you calculate entropy of universe?
ΔS sys - ΔH/T
At constant temp + pressure
What is Gibbs Free Energy equation?
ΔG = ΔH - TΔS
What is the reaction at constant temp when ΔG < 0?
Spontaneous in forward direction
What is the reaction at constant temp when ΔG > 0?
Spontaneous in backwards direction
What is the reaction at constant temp when ΔG = 0?
Reaction at eqm
What is the ΔG of any process?
The max non-expansion work that can be extracted from process at constant temp + pressure
How do you calculate standard free energies of formation?
ΔG = products - reactants
How do you calculate ΔG under non-standard conditions?
ΔG = ΔG° + RT In K
How do you calculate ΔrG°?
-RT In K
What happens when a reaction mixture is mostly reactants?
K < 1
RT In K < 0
ΔG < 0
Total free energy decreases as reaction proceeds spontaneously in forwards direction
What happens when a reaction mixture is mostly products?
K > 1
RT In K > 0
ΔG > 0
Total free energy decreases as reaction proceeds spontaneously in backwards direction
What is Ki?
Inhibitor constant
What is ionic bond value?
20-40 kJ/mol
What is polarisation effects important for?
Soft atoms
eg. sulphur
What are dispersion effects important for?
Attractive component of van der Waals interactions
What is H bonding important for?
Angular dependence which produces directionality in binding
What is H bonding drug binding?
Thermoneutral
What do organic molecules want to do in aq environment?
Come together
= hydrophobic effect = form droplets
What is effective drug design?
Compromise between enthalpic + entropic considerations
