Bailey N-
First law of thermodynamics
The total amount of energy is constant; it can neither be created nor destroyed
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Second law of thermodynamics
The availability of energy decreases as time moves forward
- As the universe expands, energy gets more spread out and becomes less useful
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Entropy can be a measure of 1)___ and can also measure 2)___
1) A measure of disorder or disorganization within the universe
2) Measure the number of equivalent ways that energy in a system can be arranged
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Equation for quantifying entropy
S = Kb · ln · W
- S is the measure of entropy
- Kb is Boltzmann's constant
- W is the number of ways energy in a system can be arranged
- ΔS represents change in entropy
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What does 'spontaneous' mean scientifically
A process that happens forward in time with no intervention or prompt
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How are spontaneous reactions and entropy related
Spontaneous chemical reactions happen by themselves without energy input and increase the total entropy of the universe
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How does spontaneity describe probability
Systems will spontaneously reach arrangements that are statistically probable and it's more probable for energy to spread out (entropy)
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What does 'non-spontaneous' mean scientifically
Reactions that do not happen on their own, but with enough energy input we can cause a non-spontaneous process or unfavorable reaction
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Rank state phases from least to most entropy
Solid (least) < liquid < gas (most)
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Standard molar entropy (S°)
Entropy of 1 mole of a substance under standard conditions
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Three trends in standard molar entropy values
1) solid phases have the lowest entropy values, gases have the highest
2) For similar substances (elements in the same column) entropy values increase as molar mass increases
3) more complicated molecules with more atoms tend to have higher entropy values
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In a chemical reaction, more moles of gas means ___ entropy, less moles of gas means ___ entropy
More moles of gas → higher entropy
Less moles of gas → lower entropy
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Equation for calculating entropy change in system (ΔS° or ΔSsys)
ΔS° = ∑npS°p - ∑nrS°r
n = molar coefficient of substance
p = products
r = reactants
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Equation for calculating entropy change in surroundings (ΔSsurr)
ΔS°surr = (-ΔH°sys) ÷ T
- (-ΔH°sys) = enthalpy of reaction (q = m · Cs · ΔT)
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How are temperature and volume related to entropy
Temperature increases → entropy increases
Volume increases → entropy increases
- Only if one or the other is CONSTANT!
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When a pure substance is mixed, entropy ___, when it's separated, entropy ___
Mixed together → entropy increases
Separated → entropy decreases
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Equation for calculating entropy change for the universe (ΔS°uni)
ΔS°uni = ΔS°sys + ΔS°surr
- ΔS°surr = (-ΔH°sys) ÷ T
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Useful (free) energy (G°)
- The amount of useful energy gained from a spontaneous reaction
- The amount of energy input needed to move a non-spontaneous reaction forward
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Equation for calculating free energy change (ΔG°) (what is it measuring)
ΔG° = ΔH°sys - TΔS°sys
- measures the difference in free energy between the left and right side of a reaction
Find ΔH° and ΔS° using ∑nproducts - ∑nreactants
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If ΔG° is negative then the reaction is ___
If ΔG° is positive then the reaction is ___
- ΔG° = spontaneous
+ ΔG° = non-spontaneous
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If [ΔH° < 0 & ΔS° > 0] then ΔG° ...
Impossible for ΔG° to be positive (ΔG° < 0)
- Spontaneous for all values of T
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If [ΔH° > 0 & ΔS° < 0] then ΔG° ...
Impossible for ΔG° to be negative (ΔG° > 0)
- Non-spontaneous for all values of T
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If [ΔH° > 0 & ΔS° > 0] then ΔG° ...
Spontaneous at high values of T
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If [ΔH° < 0 & ΔS° < 0] then ΔG° ...
Spontaneous at low values of T
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Equation for free energies of formation (ΔG°f) and when it can be used
ΔG° = ∑npΔG°fp - ∑nrΔG°fr- Can ONLY be used when energy change happens at 298K, cannot be used for any other value of T
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Chemical equilibrium in relation to free energy
Equilibrium = When there's no difference in free energy (ΔG° = 0)
- After all free energy that can be is released, it goes in both directions at the same speed
- No difference in energy because the energy cannot spread out more than it already is
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Find ΔS° using the free energy equation
ΔS° = (ΔH° - ΔG°) ÷ T
- ΔG° value usually given
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Find T using the free energy equation
T = (ΔH° - ΔG°) ÷ ΔS°
- ΔG° is usually 0
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What value is ΔG° at a substance's boiling or melting point
Boiling or melting point of a substance → ΔG° = 0
- This is because during a state change, the amount of energy being used to melt a substance is the exact same as the amount being used to re-solidify it
