Entropy & Spontaneity - entropy Flashcards
What is entropy (S) in a given system?
The number of possible arrangements of the particles and their energy in a given system
It is a measure of how disordered or chaotic a system is.
What happens to entropy when a system becomes more disordered?
Entropy will increase
An increase in entropy means that the system becomes energetically more stable.
What state has the highest entropy?
Gas - it is the most disordered as the particles are constantly moving around
How does the formation of a gas molecule in a reaction affect entropy?
Entropy increasaes as the system has become more disordered.
The formation of the gas molecule CO2 signifies increased disorder.
How does melting of ice affect entropy?
Entropy increases when solid ice melts into liquid water
Water molecules in ice are in fixed positions, while in liquid they move more randomly.
What does a higher entropy indicate about a system’s energy?
The energy of the system is more spread out when it is in a disordered state
Systems with higher entropy are energetically favorable.
What do standard molar entropy values (Sꝋ) relate to?
Standard conditions of temperature and pressure
These values are used to calculate entropy changes.
How is the entropy change (ΔSꝋ) calculated?
ΔSꝋ298(reaction) = ΣSꝋ298(products) - ΣSꝋ298(reactants)
This equation is provided in the data booklet.
What are the units of ΔSsystemꝋ?
J K^-1 mol^–1
This unit measures the change in entropy.
How does the state of matter affect entropy values?
Entropy values will be different for the liquid and gaseous phases
For example, Sꝋ298(H2O (l)) = 70.0 J K-1 mol–1 and Sꝋ298(H2O (g)) = 188.8 J K-1 mol–1.
In the reaction N2O4 (g) → 2NO2 (g), how should the coefficient be applied when calculating ΔSꝋ?
Double the value for Sꝋ (NO (g))
This is necessary to balance the equation correctly.
