module 5: thermodynamics Flashcards
define enthalpy change of atomisation
the enthalpy change when 1 mol of gaseous monoatomic element is formed from elements in its standard state
define lattice enthalpy
the enthalpy change when 1mol of an ionic solid is made from the gaseous ions
represents ionic lattice bonding strength, always exothermic
outline how you would structure a born-haber cycle
1st ionisation: e-
2nd ionisation: 2e-
what factors can affect lattice enthalpy and why
ionic charge and ionic radius
high ionic radius = low lattice enthalpy
smaller ions can get closer and have stronger attraction
high ionic charge = high lattice enthalpy
greater charge means electrostatic attraction is stronger
what is charge density
it’s dependent on ionic radius and ionic charge, a higher charge density gives rise to a greater lattice enthalpy
what is entropy (S)
a measure of the disorder of energy/how spread out it is
how does an equation show whether entropy has increased or decreased
gases are more disordered than liquids and solutions which are more disordered than solids as they have more movement
so entropy has increased if there is a higher number of moles of items that are more disordered and vide versa for decreased entropy
increase in entropy: CaCO3(s) → CaO(s) + CO2(g)
what is meant by feasible or spontaneous reactions
the idea that reactions are energetically favourable and therefore should occur
but it may not take place because of a high activation energy etc.
they will always have an entropy change > 0
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how are exothermic reactions linked to entropy
exothermic reactions transfer heat to surroundings and so increase the energy disorder of the surroundings and so increasing entropy of surroundings
how are endothermic reactions linked to entropy
in endothermic reactions thermal energy is transferred from the surroundings into the system
this decreases energy disorder and so entropy of the system
how can the total entropy change for any process be calculated
for any process, total entropy change is equal to entropy change of system plus entropy change of surroundings
how is the standard entropy change (ΔS) of a system calculated
ΔS = entropy of products - entropy of reactants
what equation calculates Gibbs free energy change
if deltaG is negative that means that the reaction is feasible/spontaneous
what do you assume when finding the temperature at which a reaction would be spontaneous
that deltaH and deltaS aren’t affected by temperature
how do you know what sign should be on a value that was calculated using an energy cycle?
look at the arrow direction
down: negative bc it’s exothermic
up: positive bc it’s endothermic
what do you refer to when asked about how enthalpy changes differ in a question that has previously mentioned lattice enthalpy
ionic radius
lattice enthalpy
how each type of enthalpy change involved would be affected
define enthalpy change of hydration
the enthalpy change when 1 mole of gaseous ions dissolve in water to form an infinitely dilute solution
define enthalpy change of solution
enthalpy change when 1mole of ionic substance dissolves in sufficient water to form an infinitely dilute solution
can be endo/exothermic
how is an equation to show enthalpy of solution written
how is an equation to show enthalpy of hydration written
is enthalpy of solution exothermic or endothermic
can be either
is enthalpy of hydration endothermic or exothermic
exothermic because it’s the energy released when an attraction forms between ions and water molecules
explain enthalpy of hydration
an ionic solid dissolves in water, forming positive and negative ions to form ion-dipole attractions with water
the O is attracted to positive ions whilst the H is attracted to negative ions
what is the relationship between enthalpy of solution and enthalpy of hydration
