gibbs free energy Flashcards

1
Q

What is entropy?

A

The measure of disorder of a system

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2
Q

Symbol for entropy change

A

ΔS

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3
Q

What affects the entropy of a system?

A

gases > liquids > solids
greater Mr = greater entropy
number of species, more species = greater entropy

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4
Q

How to calculate entropy change

A

ΔS = sum of entropy of products – sum of entropy of reactants

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5
Q

What does a positive (+) ΔS mean?

A

entropy has increased

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6
Q

How to calculate enthalpy change using ΔH formation data

A

ΔH = sum of ΔHf products – sum of ΔHf reactants

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7
Q

Gibb’s Free-energy equation

A

ΔG = ΔH - TΔS

T must be in Kelvin (oC +273)
ΔS must be in kJ K- mol-1 (/1000)

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8
Q

What does ΔG mean

A

if ΔG is zero or negative a reaction is feasible

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9
Q

Why do some reactions not occur even if feasible?

A

the activation energy is too high

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10
Q

Calculate the temperature at which a reaction becomes feasible

A

ΔG is zero when reaction becomes feasible
0 = ΔH - TΔS, therefore T = ΔH/ΔS
T must be in Kelvin (oC +273)
ΔS must be in kJ K- mol-1 (/1000)

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11
Q

Using a graph to calculate ΔG

A

ΔG = ΔH - TΔS

ΔG = - ΔS T + ΔH
y = -mx + c

Plot ΔG vs. T, ΔH = intercept (c), -ΔS = gradient (m)

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12
Q

give the equation for temperature at which reaction just becomes feasible

A

T = ΔH/ΔS

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