Topic 13 Entropy Flashcards
What is a spotnaneous process
One that takes place without continuous intervention from us, reverse will never happen on its own
Define Entropy and what do systems tend towards
A quantity associated with randomness or disorder, always want higher entropy
What total entropy change is there in spontaneous reaction
Positive
How to calculate total entropy
Change in system + Change in surroundings
How to caluculate entropy change of system
products - reactants
Calculate entropy change of surroundings
Surroundings = minus Change in enthalpy / temperature (kelvin)
How does temperature impact entropy
Increase in temperature at higher entropy has less positive effect than at lower entropy (temperature)
Why may a reaction that is not thermodynamically feasible occur
Non standard conditions
How to calculate Gibbs Free Energy
Change in enthalpy - T(entropy change system)
What does different values for Gibbs Free Energy mean
positive - not feasible
negative - feasible
0 = equilibrium
Equilibrium constant Gibbs Free energy equation
Gibbs = -RTlnK
Why may a reaction that is thermodynamically not feasible occur
Higher activation than the temperature it is spontaneous at. Called kinetic stablility
Experimental vs theoretical lattice energy
Experimental is calculated through Born Haber Cycle, theoretical is done using calculations
Assumptions made with theoretical lattice energy
Ions are in contact with each other
Ions are perfectly spherical
Charge on each ion is evenly distributed around the centre so that each ion can be considered as point charges
Why may experimental be higher than theoretical
Covalent properties of lattice structure due to polariation of anion
Factors affecting polarisation of anion
High charge and small size of cation . charge density high
Factors affecting polarising ability of cation
High charge and large size of anion. most easily polarised
Lattice Energy, ΔlatticeHꝊ
The energy change when one mole of an ionic solid is formed from its gaseous ions under standard conditions
Provides a measure of ionic bond strength
Enthalpy Change of Atomisation, ΔatHꝊ
The enthalpy change when one mole of gaseous atoms are formed from an element in its standard state.
Electron Affinity, EeaꝊ
The energy change when one mole of electrons is gained by one mole of gaseous atoms or anions to form one mole of gaseous anions.
Enthalpy change of solution, ΔsolHꝊ
The enthalpy change when one mole of an ionic solid dissolves in excess water to form an infinitely dilute solution.
Enthalpy Change of hydration, ΔhydHꝊ
The enthalpy change when one mole of an ion in its gaseous state is
completely hydrated by water to form an infinitely dilute solution.
Dissolving ammonium nitrate in water
Entropy change is positive
Endothermic Reaction
Solid to aqueous. 1 mol to 2 moles
Ethanoic acid with ammonium carbonate
Bubbles of gas are violently produced
Endothermic
Entropy positive
gas is produced
Magnesium ribbon burnt in air
Highly exothermic
entropy system negative but total positive
Doesn’t occur at room temp due to activation energy being too high
