2.3 Entropy & Spontaneous Change Flashcards
What is a spontaneous process?
process occurring in the absence of any ongoing outside intervention
In what direction do spontaneous reactions occur?
in one direction
–> reactions are non spontaneous in the reverse direction
Does exothermic or endothermic reactions occur spontaneously?
either
What is entropy (S)?
MEASURE OF THE RANDOMNESS OF A SYSTEM
How does entropy increase?
higher number of possible arrangements (mixing possibilities
–> mixing is a spontaneous reaction
∆S > 0
How are reaction rate and spontaneity related?
they are not; being spontaneous has nothing to do with speed
Is entropy a state function?
Yes! ∆S = S(final) - S(initial)
Does nature favour high entropy?
yes, nature favours more disorder
How can low entropy be produced?
adding energy to create order
–> will create entropy somewhere else
What impacts entropy?
temperature and phase change
increase temp increase entropy
S(gas) > S(liquid) > S(solid)
What impacts entropy more: temperature or state change?
state change
Is the entropy of fusion or vaporization larger?
vaporization
Why does entropy increase with temperature?
measuring kinetic energy of molecular motion: translational, vibrational, and rotational motion
Is there motion at absolute zero? (0ºK)?
no translational or rotational motion, but atoms have vibrational
What is zero-point vibrational energy?
explains vibrational motion at absolute zero
- as atoms are warmed, molecules in the solid begin to vibrate more = increase in atomic/molecular positions = increase in entropy
How can chemical reactions affect entropy?
if section involves 1+ reactants or products in the gas phase
How does number of molecules impact entropy>
increase # of molecules in gas phase = increase entropy because two moles of gas particles have more freedom of motion = more possible arrangements
What is the 2nd law of thermodynamics?
every spontaneous process increases the entropy of the universe
∆S(Universe) = ∆S(sys) + ∆S(surr) > 0
How can you determine if a process is spontaneous?
determine if the process is associated with an overall increase of entropy to the universe
Is it possible for a spontaneous process to have ∆S (sys) < 0?
Yes, if ∆S(surr) > 0 is very large
What is the 3rd law of thermodynamics?
entropy of a perfectly ordered crystalline solid is defined to be zero at a temperature of absolute zero
What is the implication of the 3rd law?
absolute entropies can be measured because there is a definition of zero entropy
What is standard molar entropy (Sº)?
absolute entropy of 1 mole of a substance in its standard state
J/mol*K
How can ∆Sº be calculated?
∑Sº (products) - ∑Sº (reactants)
What is the relationship between number of atoms and entropy?
increasing number of atoms = more motion = more possible arrangements = larger molecules = increase entropy
Ex. C3H8 > C2H6 > C2H4 > CH4
