Lecture 3: Thermodynamics and Weak Molecular Interactions Flashcards
What do thermodynamics tell us?
 Which reactions are possible 2. What directions do reactions take
What is the 1st Law of Thermodynamics (law + equation)?
 Energy is conserved  it is neither created nor destroyed
 ΔU = Ufinal – Uinitial = q  w
ΔU = total energy of the universe, unit = Joules (J)
q = heat absorbed by a reaction
w = work done by the reaction
What does ΔU = 0 mean?
It means that the heat absorbed by the reaction is equal to the work done by the reaction
What does it mean when a unit is capitalized?
It is a state function, meaning it is INDEPENDENT of path
What are examples of nonstate functions?
Work and rate of rxn
What is the definition of enthalpy?
The total heat content of a system, H
What is the equation to calculate enthalpy? Unit?
H = U + P.V Unit = J
What is bond enthalpy?
The energy stored in chemical bonds
What is the sign of ΔH for exothermic reactions?

What is the sign of ΔH for endothermic reactions?
+
What is an example of an exothermic rxn?
Bond breaking
What is an example of an endothermic rxn?
Bond formation
Can endothermic reactions occur spontaneously?
Yes!
What is the 2nd Law of Thermodynamics? Why?
The universe tends towards maximum disorder because there are many more probable ways of being disordered than ordered.
What is entropy, S?
It is a measure of disorder or randomness
What is the equation to calculate entropy?
S = kB.ln W
unit = Joules/Kelvin (J/K)
kB = Boltzmann constant (1.3807 x 1023 J/K)
W = number of ways
What does the Boltzmann constant correspond to?
The gas constant divided by Avogadro’s number
What are examples of energy investments to maintain order?
DNA repair, ordering books in a library
What is the Boltzmann constant? What does it correspond to?
kB = 1.3807 x 1023 J/K
Corresponds to the gas constant divided by Abogadro’s number
How do temperature and entropy relate to each other?
Entropy increases as temperature increases
What are the 2 mathematical ways of saying that entropy always increases? What do they mean?
 For ΔU = 0, ΔSsystem + ΔSsurroundings = ΔSuniverse > 0
 ΔS >/= q/T q: heat absorbed by the system
They mean that not all of thermal energy in a system can be converted to useful work
What is an example of a system gaining order at the expense of its surroundings?
Protein folding disorders the aqueous surrounding, formation of lipid bilayer disorders the water surrounding
What is Gibbs free energy used for?
To determine spontaneity
What is the equation to calculate G?
ΔG = ΔH – TΔS
What is the sign of ΔG for spontaneous reactions?

What is the sign of ΔG for nonspontaneous reactions?
+
In what direction do rxns go?
Direction of lower free energy
How can one make an endergonic rxn happen? 2 ways
 Couple it to an exergonic rxn 2. Change the concentrations of reactants/products