Thermodynamics Flashcards
What is the enthalpy of lattice formation?
What is the enthalpy of lattice dissociation?
How is the theoretical lattice enthalpy calculated?
Using the perfect ionic model.
What is the perfect ionic model?
It assumes that all the ions are perfectly spherical and have their charge evenly distributed around the compound.
How is the experimental lattice enthalpy calculated?
Born-Haber cycles
Why are the experimental and theoretical values different?
Some ionic compounds have some covalent character and that causes the experimental values to be more exothermic as the bonds are stronger.
How does covalent character form?
The smaller positive ions attract the negative and larger ions towards them and this distorts the ions and creates covalent character.
Why is the enthalpy change for an exothermic reaction negative?
Because more energy is released when bonds are made.
Why is the enthalpy change for an endothermic reaction positive?
Because more energy is taken in to break bonds.
What is entropy?
A measure of how much disorder there is.
Why do gases have more entropy compared to solids and liquids?
Solids only vibrate about a fixed point and liquids spread out a bit more but they are still in a fixed position. Gases move around rapidly and randomly which means they have much more disorder.
How does the amount of particles you have affect entropy?
The more particles you have the more entropy there is.
How do you calculate entropy changes?
products-reactants (J)
What is the equation for Gibbs free energy?
∆G = ∆H – T∆S ( kJ)
When is a reaction feasible?
When ∆G is less than 0.
