Topic 13 - Entropy Flashcards
What is lattice energy?
The energy change when one mole of an ionic solid is formed from its gaseous atoms
What is the enthalpy change of atomisation?
The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state, under standard conditions
What is electron affinity?
The energy change when each atom in one mole of gaseous atoms gains an electron, forming -1 ions
What is lattice energy provide a measure of?
Ionic bond strength
Why is less energy released upon hydration of I-(g) than Na+(g)?
- I-(g) has a larger ionic radius
- So less electrostatic forces of attraction between the ions and the water molecules
- Na+(g) has a smaller ionic radius
What determines lattice energy?
- Charge of ion
- Size of ionic radius
What is entropy a measure of?
Disorder in a system
How does the reaction between ammonium carbonate and ethanolic acid show a change in entropy? Give the equation
2CH3COOH(l) + (NH4)2CO3(S) –> 2CH3COONH4(aq) + H20(l) + CO2(g)
- Endothermic reaction
- Measure using a thermometer
- Changes in physical states
How does the reaction between hydrated barium hydroxide and solid ammonium chloride show a change in entropy? Give the equation
Ba(OH)2. 8H2O(s) + 2NH4Cl(s) –> BaCl2(s) + 10H20(l) + 2NH3(g)
- Endothermic reaction
- Changes from two solids to a solid, liquid and gas
How does burning magnesium in air show a change in entropy?
Give the equation
Mg(s) + 1/2 O2(g) –> MgO(s)
- Exothermic reaction
- Thermodynamically spontaneous
- Even though ΔSsystem is negative, ΔSsurroundings is greater so ΔStotal is positive
-ΔSsystem negative as a solid and a gas are forming a solid
What must happen in a spontaneous process?
Total entropy must increase
What happens when an ionic solid dissolves in water?
- Lattice structure is broken down
- Ions become hydrated
- Endothermic process (opposite of lattice energy)
What is the solubility of an ionic solid determined by?
Total entropy change
ΔStotal
Give the equation for working out ΔStotal when using enthalpy change of solution
ΔStotal = ΔSsystem - ΔsolH/T
What is the value of ΔStotal, hence solubility of an ionic solid, dependant on?
- Entropy change of system, ΔSsystem
- Enthalpy change of solution, ΔsolH
- Temperature, in Kelvin, T
