Gibbs energy Flashcards
What is the equation for relating Gibbs energy to entropy?
Gibbs energy = Enthalpy - (Temperature x Entropy of system)
How can you tell if a reaction if thermodynamically feasible from Gibbs energy?
If the Gibbs energy value is negative (or zero), the reaction is thermodynamically feasible.
If the Gibbs energy value is positive, the reaction is not thermodynamically feasible
What will be the Gibbs value at the minimum temperature for a reaction to be feasible?
At the minimum temperature for a reaction to be feasible, Gibbs will be 0
How can we rearrange the Gibbs equation to work out the minimum temperature at which a reaction is feasible?
T = Enthalpy / Entropy of system
What is the equation for relating Gibbs energy to equilibrium constant (K)?
Gibbs energy = -R x T x ln(K
How can we rearrange the Gibbs equation to work out equilibrium constant?
K = e^(-Gibbs/RxT)
What does an equilibrium constant greater than 1 indicate?
The products are favoured
What does an equilibrium constant less than 1 indicate?
The reactants are favoured
What does a negative Gibbs value indicate about the value of K?
It is greater than 1
What does a positive Gibbs value indicate about the value of K
It is less than 1
Although a negative Gibbs value indicates that the reaction is feasible, it may not take place… why?
There are two factors to consider when applying the concept of Gibbs:
- Kinetic stability
- Non-standard conditions
How does kinetic stability influence if a reaction occurs or not?
A reaction may have a negative Gibbs value, but not spontaneously react, as the activation energy may be very high, so few collisions result in reaction (kinetic stability)
How does non-standard conditions influence if a reaction occurs or not?
Gibbs energy is calculated under standard conditions, so a reaction may have a positive Gibbs value under standard conditions, but a negative Gibbs value (so thermodynamically feasible) when conditions are non-standard
