Enthalpy and entropy Flashcards
Define entropy
- A measure of the dispersal of energy which is greater when the system is more disordered
What is the symbol of entropy?
ΔS
Is a solid or gas more disordered?
Gas
What is the unit of standard entropy?
J K-1mol-1
How does temperature affect entropy?
- The greater the temperature particles have the more energy and they move more
When a solid ionic lattice is dissolved in a solution what happens to the entropy?
Entropy increases due to the ions being more disordered
What’s the equation used for entropy change?
S products - S reactants
What is Gibbs free energy equation?
ΔG = ΔH - TΔS
What is Gibbs free energy equation?
ΔG = ΔH - TΔS
What needs to happen for a reaction to be feasible?
ΔG < 0
What are the limitations of the predictions of feasibility made by using ΔG?
- Reaction may have high Ea
- Rate of reaction may be very slow
Define lattice enthalpy
Formation of 1 mole of ionic lattice from gaseous ions under standard conditions
What does a more exothermic lattice enthalpy mean?
More exothermic = more stronger ionic bonds
Why is it not possible to measure lattice enthalpy directly?
It is not possible to form 1 mole of an ionic lattice from its gaseous ions
Define enthalpy change of solution
Enthalpy change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions
Define enthalpy change of hydration
The enthalpy change when dissolving 1 mole of gaseous ions in water
What factors affect size of lattice enthalpy?
- Ionic size (as ionic size increases lattice enthalpy becomes less negative)
- Ionic charge (as ionic charge increases lattice energy becomes more negative)
Which ions have more negative lattice enthalpy?
Smaller ions
Describe hydration
- When an ionic lattice is broken the ions become part of the solution
- Positive ions are attracted to the slightly negative oxygen and negative ions are attracted to the slightly positive hydrogen
