x Flashcards
lattice enthalpy definition
measure of the strength of ionic bonding in a giant ionic lattice
what is the purpose of Born- Haber cycles
determines the lattice enthalpy indirectly
what sort of energy change is needed to form gaseous atoms? why?
- endothermic
- involves breaking bonds
what sort of energy change is needed to form gaseous ions?
endothermic
what sort of energy change is needed to form a lattice
exothermic
standard enthalpy change of formation definition
formation of 1 mol of a compound from its elements in its standard states under standard conditions
standard enthalpy change of atomisation definition
formation of one mole of gaseous atoms from the element in its standard states under standard conditions
first electron affinity definition
addition of 1 mol of electrons to 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions
enthalpy change of hydration definition
dissolving of 1 mol of gaseous ions in water
explain why the 2nd ionisation is more endothermic than the 1st ionisation
- Mg+ has one more proton than electrons
- increase nuclear attraction
- decrease radius
what energy is needed in the second electron affinity
enothermic
what energy is needed in the second electron affinity
endothermic
write the equation to calculate energy change
q=mc∆T
what 2 processes take place when ionic compounds dissolve in water
- ionic lattice breaks up
- water molecules are attracted to, and surround, the ions
what are the general properties of ionic compounds?
- high melting and boiling points
- soluble in polar solvents
- conduct electricity when molten or in aqueous solution
effect of ionic size on lattice enthalpy
- ionic radius increases
- attraction between ions decrease
- lattice enthalpy less negative
- melting point decreases
effect of ionic charge on lattice enthalpy
- ionic charge increases
- attraction between ions increase
- lattice energy becomes more negative
- melting point increases
effect of ionic charge size from left to right
- increasing charge gives more attraction
- decreasing size gives more attraction
effect of ionic charge size from right to left
- increasing charge gives more attraction
- increasing size gives less attraction
effect of ionic size on hydration enthalpy down group 1
- ionic radius increases
- attraction between ion and water molecules decreases
- hydration energy less negative
effect of ionic size on hydration enthalpy down group 1
- ionic radius increases
- attraction between ion and water molecules decreases
- hydration energy less negative
effect of ionic charge on hydration enthalpy
- ionic charge increases
- attraction with water molecules increases
- hydration energy become more negative
what can entropy be used to predict
- a gas spreading through a room
- heat from a fire spreading through a room
- ice melting in a hot room
general rules of entropy
- solids have the smallest entropies
- liquids have greater entropies
- gases have the greatest entropies
what will the entropy change be if a system changes to become more random
- energy becomes more spread out
- ∆S is positive
what will the entropy change be if a system changes to become less random
- energy becomes more concentrated
- ∆S is negative
when any substance changes state from solid to liquid to gas, its entropy increases:
- melting and boiling increase the randomness of particles
- energy is spread out more and ∆S is positive
describe the entropy of this reaction:
N₂(g) +3H₂(g) -> 2NH₃(g)
- decrease in the randomness of particles
- energy is spread out less and ∆S is negative
standard entropy of a substance
entropy of 1 mole of a substance, under standard conditions (100kPa and 298K)
standard enthalpy facts
- JK⁻¹mol⁻¹
- always positive
calculate entropy changes
∆S=ΣS(products)-ΣS(reactants)
calculate entropy changes
∆S=ΣS(products)-ΣS(reactants)
write the Gibb’s equation
∆G=∆H-T∆S
enthalpy change, ∆H
heat transfer between the chemical system and the surroundings
entropy change at the temperature of the reaction, T∆S
dispersal of energy within the chemical system itself
conditions for feasibility
- ∆G<0
limitations of predictions made for feasibility
rate of reaction is very slow
