TOPIC 13 - Energetics II Flashcards
What is lattice enthalpy of formation?
What is enthalpy chaange of atomisation?
What is 1st electron affinity?
What is 2nd electron affinity?
Why are Born-Haber cycles useful?
To calculate enthalpies that can’t be measured experimentally.
What is A?
Enthalpy of formation
What is B?
Enthalpy of atomisation of chlorine
What is C?
Enthalpy of atomisation of lithium
What is D?
1st ionisation energy of lithium
What is E?
1st electron affinity of chlorine
What is F?
Lattice enthalpy of formation of LiCl
Calculate lattice enthlapy of LiCl using the Born-Haber cycle
What is a perfectly ionic model?
Ions are evenly spherical in the latticeand the charge is evenly distributed (point charge)
Why are all the experimental values higher than the theoretical ?
None of them is purely ionic. There is some covalent character. The electron cloud in the anion is distorted so electrons are closer to the +ve charge, so more energy is released.
Are smaller cations more or less polarising? Why?
More polarising.
In smaller cations, the +ve charge is closer to the electrons in the anion and so electrostatic forces of attraction are greater and the electron cloud is distorted more.
Are cations with bigger charge more or less polarising?
More polarising.
Bigger charge = bigger electrostatic forces of attraction = electron cloud in anion is distorted more.
Are bigger anions more or less polarisable? Why?
More polarisable.
Electron cloud is further away from the nucleus of the anion and so electrons are more attracted to the nucleus of the cation, so electron cloud is more distorted.
What is the general rule for electronegativity in the periodic table?
Further up and right you go, electronegativity increases (excluding nobel gases).
How does difference in electronegativity affect the nature (ionic/covalent) of the bond?
The bigger the difference between the two atoms, the more ionic the bond is.
What is enthalpy change of solution?
What happens, in terms of bonds, for a substance to dissolve?
Substance bonds break - endothermic.
Bonds fromed between solvent and substance - exothermic.
For a substance to dissolve, what must the strength of the newly formed bonds be?
Same strength or greater than those broken previously.
What enthalpy of solution does a soluble substance have?
-ve enthalpy of solution (exothermic).
What is enthalpy of hydration?
What is A?
Enthalpy change of solution
What is B?
Lattice dissociation enthalpy
What is C?
Enthalpy of hydration
How does the charge of the ions affect enthalpy of hydration?
How does size of ions affect the enthalpy of hydration?
What is entropy?
The number of ways energy can be spread out between particles. It is a measure of disorder in a system.
Can an enthapically unfavourable reaction be spontaneous (feasible)?
Yes. If the change in entropy overcomes the change in enthalpy
i.e.
What is the equation for the entropy change of a reaction?
What are the standard conditions for standard entropy?
Does entropy increase or decrease in an entropically feasible reaction?
Increases.
What is the equation for total entropy change?
What is the equation for Gibbs free energy?
How does gibbs free energy tell if a reaction is feasible at that temperature?
If gibbs is 0 or -ve, reaction is feasible.
Why might a reaction not be observed even though it is feasible?
The reaction might have high activation energy and/or a slow rate of reaction.
Is a reaction feasible if it has a -ve enthalpy change and a +ve entropy change?
Yes. It is feasible at any temperature. Gibb’s free energy is -ve at any temperature.
Is a reaction feasible if it has a +ve enthalpy change and a -ve entropy change?
Never feasible. Gibb’s energy will always be positive
Is a reaction feasible if it has a -ve enthalpy change and a -ve entropy change?
Only at lower temperatures. Gibb’s free energy will only be negative in lower temperatures.
Is a reaction feasible if it has a +ve enthalpy change and a +ve entropy change?
Only at higher temperatures. Gibb’s free energy is will only be -ve at higher temperatures.
How do you calculate the temperature at which a reaction becomes just feasible?
What are the values for Kc for reactions with a -ve change in gibbs free energy?
Kc is large (greater than 1) because reaction feasible.
What are the values for Kc for reactions with a +ve change in gibbs free energy?
Kc is less than 1. The reaction isn’t feasible.
What is the equation linking gibb’s free energy and Kc?
