13. Energetics 2 Flashcards
What is lattice energy a measure of
Bond strength
Definition of standard lattice energy
The energy change when 1 mole of an ionic solid is formed from its gaseous ions under standard conditions
The more negative the lattice energy…….
The stronger the bonding
What affects lattice energy
Ionic charge and Size of the ions
Hess’s law states….
The total enthalpy change of a reaction is always the same no matter which route is taken - conservation of energy
You can use ….-….. …… to calculate lattice energies
Born haber cycles
What happens when solid ionic lattices dissolve in water
The bond between the ions break - endothermic
The enthalpy change is the opposite of the lattice enthalpy
Bonds between the ions and water are made - Exothermic
The enthalpy change here is called the enthalpy change of hydration
Definition of the enthalpy change of hydration
The enthalpy change when 1 mole of gaseous ions dissolve in water
Definition of the enthalpy change of solution
The enthalpy change when 1 mole of solute dissolves in water
What is entropy
A measure of the disorder of a system.
It tells you the number of ways that particles can be arranged and the number of ways energy can be shared out between the particles
The higher the entropy the …… the disorder
Higher
How does physical state affect entropy
Solid particles have lots of order so have a low entropy
Gas particles are the most disorder so have the highest entropy
How does dissolving affect entropy
Dissolving a solid increases the entropy as the particles can now move freely as they are no longer held in on place
How does more particles affect entropy
The more particles there are, the more ways the energy can be arranged therefore entropy increases because the number of moles increases
What does feasible mean
The reaction can happen without the addition of energy
More arrangements means more……
Stability
Substances are more energetically stable when there’s more disorder so particles will move to try to increase their entropy.
How to calculate the entropy change of a system
S system = S products - S reactants
What does a positive entropy change mean
That a reaction is likely to be feasible
Total entropy change =
S total = S system + S surroundings
Change in entropy of surroundings =
S surroundings = - change in H/T
H is enthalpy change
T is temperature in Kelvin
Free energy change is
The tendency of a process to take place
It is dependent on entropy, Enthalpy, and the temperature.
What does free energy (change in G) tell you
If a reaction is feasible or not, the more negative the value of change in G is the more feasible the reaction.
Change in free energy =
Change in H - (temperature x entropy change of the system)
What does G = 0 mean
The reaction is just feasible
What is an equilibrium constant
A measure of the ratio of the concentration of products to reactants at equilibrium for a reversible reaction at a specific temperature
Value of equilibrium constant for negative change in Gibbs
Greater than 1
Value of equilibrium constant for positive Gibbs
Smaller than 1
