Module 5- Intro To Entropy Flashcards
What are the standard units of entropy??
Joules/kelvin/mole
What is entropy?
A measure of how much energy is required to keep particles/molecules in order ie as a solid
What happens to entropy as particles get less ordered??
- Entropy increases
- more energy required to keep disorders particles together, but therefore they have less energy
What is the entropy at 0 kelvin of anything?
Entropy if any molecule is 0, no energy required to keep things in order because things can’t move
What’s a positive entropy change??
When reactants get more disordered, (S+Ve) ie from a solid to aqueous or gaseous state
Why is a positive entropy change favourable??
Because energy is lost from the system as things get more disordered (although to reorder them they’d need more energy), so things are more stable eg solid NaCl-> aqueous NaCl
How does number of particles/molecules affect entropy??
More particles and molecules increase entropy because they need more energy to keep them together (more opportunity for disorder)
What must entropy be for a reaction to be feasible??
TOTAL entropy change must be positive for a reaction to be feasible
What’s the equation for total entropy change??
🔼S total= 🔼S system + 🔼S Surroundings
What are the equations for 🔼S system and 🔼S surroundings
🔼S system= entropy change of products - entropy change of reactants
🔼S Surroundings= - 🔼H (ENTHALPY) / Temperature in kelvin
What do you need to remember when working out entropy totals??
- The units of entropy are joules/K/Mole but enthalpy is in KJ/mole so that must be converted appropriately
- there’s a minus sign in front of the delta H
- convert degrees Celsius to kelvin (+273)
What is Gibbs free energy for??
Combining entropy and enthalpy to work out if reactions are feasible at room temp/ any temp
Equations for Gibbs free energy
🔼G = 🔼H - T(temp in Kelvin) x 🔼S System (must be converted into KJ before using with enthalpy)
When is a reaction feasible at room temperature??
If 🔼G is NEGATIVE, the reaction is feasible at that given temperature, but the reaction first becomes feasible when 🔼G= 0
How do you work out the point at which a reaction becomes feasible??
State “ when G=0, 🔼H= T x 🔼System, and therefore T= 🔼H / 🔼S system’
Then convert entropy of system into KJ and use equation to work out temp in kelvin, the temperature at which it becomes feasible
