# Chemistry 3.7 - Entropy

What does entropy measure?
The disorder of a system.
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If a solid becomes a liquid, is the entropy low or high?
HIGH. The molecules have increased free movement and so increased disorder.
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How do we calculate entropy change?
Entropy = Σproducts - Σreactants
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If the entropy change is negative...
There is less disorder (e.g. gas --> liquid).
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If the entropy change is positive...
There is more disorder (e.g. solid --> liquid).
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Entropy units?
Jmol-1K-1 (for Gibbs free energy it must be in KJmol-1K-1). This is achieved by dividing by 1000.
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Gibbs free energy equation?
ΔG = ΔH - TΔS
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ΔG units?
KJmol-1
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ΔH units?
KJmol-1
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ΔG is positive?
The reaction is not likely to occur.
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ΔG is negative?
The reaction is likely to occur spontaneously.
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ΔG = 0?
This creates an equilibrium between the reaction occurring and not occurring. The reaction is just feasible, BUT not spontaneous.
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When calculating the enthalpy change for Gibbs free energy, do the arrows go up or down in the cycle?
UP.
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If the entropy change is positive, how will this effect the spontaneous occurrence of the reaction?
Entropy has increased, which means increasing the temp will cause - TΔS to become more negative. ΔG will become more negative and so the reaction is more likely to occur spontaneously.
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If the entropy change is negative, how will this effect the spontaneous occurrence of the reaction?
Entropy has decreased, which means decreasing the temperature will cause - TΔS to become smaller. The reaction will therefore be less positive.
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## Other cards in this set

### Card 2

#### Front

If a solid becomes a liquid, is the entropy low or high?

#### Back

HIGH. The molecules have increased free movement and so increased disorder.

### Card 3

#### Front

How do we calculate entropy change?

### Card 4

#### Front

If the entropy change is negative...

### Card 5

#### Front

If the entropy change is positive...