Entropy Equations

Question 1

A reaction is more likely to be feasible…

Answer 1

If there is an increase in entropy (thus increase in disorder) from reactants to products
Shown by a positive total entropy value

Question 2

When working out if a reaction is feasible, what do we need to take into account?

Answer 2

The entropy change, if it’s positive means an increase in disorder thus increase in stability
Which is effected by the enthalpy change, if heat is given out then there is more disorder as more arrangements of energy

Question 3

What links the entropy change and enthalpy change?

Answer 3

Gibbs free energy

Question 4

Gibbs free energy symbol

Answer 4

🔺G

Question 5

Gibbs equals…

Answer 5

🔺H - T🔺Sₛᵧₛₜₑₘ
-T🔺S ₛᵤᵣᵣₒᵤₙ𝒹ᵢₙ𝓰ₛ

Question 6

If Gibbs is above 0…

Answer 6

The reaction is not feasible

Question 7

If Gibbs is below 0…

Answer 7

The reaction is feasible

Question 8

What to ensure when calculating Gibbs?

Answer 8

The units for enthalpy and entropy are the same eg either in J or KJ

Question 9

If a reaction is feasible does that mean it will necessarily happen?

Answer 9

No because there are kinetic factors such as the activation energy being too high so not enough molecules can collide with sufficient enough energy to overcome the activation energy

Question 10

A negative enthalpy value (exo) and positive entropy value means….

Answer 10

Using the equation, the calculated Gibbs value will be negative no matter the values
So at all temperatures this reaction is feasible

Question 11

A positive enthalpy value (endo) and a negative entropy value means…

Answer 11

The reaction will never be feasible because the calculated value of Gibbs using the equation will always be positive
So no matter the temperature this reaction is not feasible

Question 12

A negative enthalpy (exo) and negative entropy value means…

Answer 12

The reaction is only feasible at lower temperatures
So in the equation, the calculated value of Gibbs will only be positive if we have a small temperature value

Question 13

A positive enthalpy (endo) and positive entropy value means..

Answer 13

The reaction is only feasible at high temperatures so the calculated Gibbs value is only positive if the temperature is high

Question 14

How can we calculate the temperature a reaction is only just feasible at, if it depends on the temperature?

Answer 14

By setting the value of Gibbs to be 0 when a reaction is only just feasible
In the equation 🔺G = 🔺H - (T x 🔺S system)
Rearrange…
Temp = enthalpy/entropy system

Question 15

Units of Gibbs

Answer 15

kj mol-1
Or J mol-1