Module 5.2 Flashcards
Lattice enthalpy
Is the enthalpy change that accompanies , the formation of one mole of an ionic lattice from its gas deity ions under standard conditions .
Standard enthalpy change of formation
Is the enthalpy change that accompanies the formation of 1 mole of a compound from its elements .
First ionisation energy
Is the enemy change that axioms
It’s the removal of 1 mole of electron for, 1 mole of gaseous aroma
Why do ionic substances form (1)
As you learned in ionic substances are formed when ions attract one another and bond thriugh electrostatic interactions. However , in order to form a huge amount of energy is required . So why do stable elements of on to form form ions I’d so much energy is needed .
When do ionic substances form (2)
Ionic substances are formed when ions attract one another and bond through electrostatic interactions . However , in order to form ions a huge amount of energy is required . So why do stable elements of ont of or m ions if so much energy is needed l
When do ionic substances formed (2)
When oppositely charged ions attract one another , forming a giant ionic lattice , there is a h
UFE lowering of the energy the amount of initial energy , required to for, ions in large , the lowering of the energy on forming the lattice more than compensate for this , bene strong aggrcaruin . So although.
This is the reason that ionic substances have
- very strong ionic binder
- very Hugh melting and bolining point .
Measur the amount of energy involved of ionic lattice
Using lattice enthalpy . This is the enthalpy
Change when one mole of a solid ionic lattice forms from its gaseous ions under standard codnurisn .
look at page 53 d
For the solid ionic
The ions are both gaseous
One mole of the susbqtnxww is formed .
The enthalpy change is negative - energy is released to the shrrodunigs ,
Ionic lattice formsrjkn us exorhermkc .
Lattice enthalpy
More exothermic lattice enthalpy values means stronger ionic binds .
Lattice enthalpy (2)
More exotehrmic lattice enthalpy values means higher melting and boiling points as more energy is required to overcome the interactions present .
Lattice enthalpy (3)
The most exotehrmic lattice enthalpy esy arise when ions seems,all and ahve large charges + as the chargers cause large electrostatic forces and smaller ions can get closer together .
Born Haber cycles (1)
A continuous cycle is formed that can start at the elements and end at the elements .
Born haber chcles (2)
It includes one step that shows the former ion kf one mole of solid ionic lattice from t he gaseous ions . This corresponds to Thor lattice enthalpy .
Born Haber cycle (3)
The s show intermediate changes that correspond to key enthalpy changes that can be measured .
Born Haber cycle (4)
The lattice enthalpy can be calculated by applying Hess law . If a reaction can take place via more that one route and the initial and final conditions ade fhe same , the total enthalpy for each route is the same .
Key enthalpy changes
Element shave to go through a series of steps before they are ready to form ionic lattices . These chances have enthalpy changes associated with them . They key enthalpy changes are given below .
what is the standard enthalpy change of formation - check for equation
the standard enthalpy change of formation is one mole of a compound formed from its constituent elements in their standard states .
what is the standard enthalpy change of atomisation
one mole of gaseous atoms formed from its elements in its standard states .
-always an endothermic process .
what is first ionisation energy ?
one mole of gaseous 1+ ions formed from gaseous atoms . It is an endothermic process because the electron being lost has to overcome attraction in the nucleus in order to leave the atom .
what is the second ionisation energy?
for the second ionisation energy m, one mole of gaseous 2+ ions are formed , from one mole of gaseous 1+ ions .
-The first ionisation energy is an endothermic process , because the electron being lost has to overcome the attraction from the nucleus .
what is the first electron affinity
electron affinity is essentially the opposite of ionisation energy , the addition of electrons rather than the removal of electrons . For the first electron affinity is one mole of gaseous 1-ions is formed from gaseous atoms . This is an exothermic process , because the electron is attracted into the outer shell of an atom by the nucleus .
what is the second electron afffinity
one mole of gaseous 2- ions is formed from gaseous 1- ions .
-This is an endothermic process because the electron is repelled by the 1- ion.. This repulsion has to be overcome by .
check the steps to create a born Haber cycle
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check page 58-59 , 60-61 for born Haber cycles
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what is the standard enthalpy change of solution ?
It is the enthalpy change that takes place when one mole of a solute is completely dissolved in water under standard conditions .
What is the standard enthalpy change of hydration
enthalpy change that takes place when dissolving one mole of gaseous ions in water .
What happens when a solid dissolves ?
Two things occur ;
-the ionic lattice breaks down
-the free ions become part of the solution (hydration )
what dictates the size of lattice enthalpy
-the size of the ions involved .
-the charges of the ions
-the ionic bond strength (which is dependant on ionic size and charge )
why do smaller ions give more negative values
smaller ions have a smaller ionic radius , they can get closer together , this will attract one another more strongly , and give rise to exothermic lattice enthalpy values .
y do ions with a higher charge cause greater electrostatic attraction which means what
in turn more exothermic enthalpy values / The most exothermic latttice enthalpy values arise from smallhihgly charged ions .
how do ions get hydrated
once the ionic lattic has broken down into its constituent ions ,these have to become part of the solution ,this is known as hydration , . Ions are abl to do this if the oslvent can interat in simialr ways to bonding in the lattic . Ionic solids are therefore able to dissolve in polar solvents lke water .
what happens during hydration (1)
the positive ions will become attracted to the slightly negative oxygen in the water molecules .
what happens during hydration (2)
the negative ions will be attracted to the slight positive hydrogens in the water molecules .
what happens during hydration (3)
the water molecules will completely surround the ions .
what dictates the magnitude of the enthalpy of hydration
it is dependant on the size of the ions involved
-the charges of the ions
how does having a smaller ion dictate the magnitude of enthalpy of hydration
ions with a smaller ionic radii can get closer to the water molecules and are able to attract them more strongly . This means that on hydration , more energy is released and becomes more exothermic .
how does a higher charge mean a greater attraction with the water molecule
it will be more negative and hence more exothermic value for the enthalpy of hydration .
the ionic solid and the gaseous ions ca be linked by what two factors
-lattice enthalpy
-standard enthalpy of solution along with standard enthalpy of hydration .
things to note for a born Haber cycle
-ionic solid is at the bottom of the cycle.
-gaseous ions are at the top of the cycle
things to note for a born haber cycle (2)
-the rout via lattice enthalpy is shown on the left
-the route via enthalpies of solution and hydration is shown on the right .
ENTHALPY CHANGE OF SOLUTION does not correspond to the overall enthalpy
upwards = endothermic
downwards = exothermic .
What is entropy
it is the quantitative measure of the degree of disorder in a system .
What is the standard entropy
it is the substance is the entropy content of one mole of the substance under standard conditions .
what is the standard entropy change of reaction
it is the entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions , all reactants and products being in their standard state .
more disordered particles are …
higher entropy of the system
all substances above 0K possess a degree of disorder as they are in constant motion . what does this mean ?
-entropy is a positive number above 0
-at 0k , entropy is zero which is perfect crystals .
what is a useful way to think about entropy
more spreading out of energy = higher entropy
more random arrangeemnts of particles = highger entropy
why may entropy decrease
water freezing would represent a decrease in entropy as liquid has become more ordered solid with lower levels of energy dispersal .
why are entropy values dependant on temperature
-particles at higher temperatures become mroe random .
-the arrangement of particles at higher temperatures become more random
-entropy of solids , entropy of liquis , entropy f gases .
entropy changes when dissolving ionic solids
if a reaction results in products that allow more disorder , there are more ways for energy to be arranged or dispersed , then entropy will increase .
-If a solid ionic lattice dissolves , ions can spread out and the positions of the ions are far more disordered than within the lattice . This means entropy increases .
How does the number of gas molecules affect entropy
-An increase in gas molecules can cause an increase in entropy
whereas a decrease in gas molecules can decrease entropy .
if a change makes a system more positive …
s is positive
if a change makes a system more ordered
s is negative
what is free energy
free energy is the balance , between enthalpy , entropy and temperatures for a process .
what is spontaneous change
for a process to happen spontaneously , i.e. intravenously entropy must increase . But there are many examples of reactions that happen spontaneously , that would seem to lower entropy .
-FOR EXAMPLE , metal rusting in oxygen or gas condensing .
how do you calculate total change in entropy
s-total = system + surroundings
-For spontaneous changes to occur , the total change in entropy must be positive .
-Reactions that have a decrease in entropy can occur spontaneously if the changes in entropy of the surroundings , is positive enough o make the total change in entropy positive .
What is free energyn
Chabged in entropy are linked with energy changes that occur during a egreacfion or a cnHgs . We
What have reactions and processszz been considered in terms of snfjLpy jMhsz
Js l idk
What is the gibbs equation
The energy that comes free during a reaction . I’d knoej ac five free everfyv
What is gibs free energy dependant
It is dependant on the torso entropy and enthalpy changed thsy occur as well as being dependent k tenowrdtew .
What is the free energy change cakztkatuj
It is calctlstec yay c the gibbs equation
For a twxdyoohbtk occur arghh
Using the gib equation to predict feasibility of factions
Large increases in entropy will cause decrease in g because the term TS will become larger .
What do large NEGATIVE values for entropy entail
highly exothermic reactions which will result , iun more negtive values.
how is there a balance to be struck in exothermic reactions
for example. G may be positive , i whuch change would not b spontaneous . if a reaction is highly exothermic , this causes a large decrease in entropy .
check feasibiliyy table on page 69
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free energy and summary about exothermic reactions
exothermic reactions are generally spontaneous - the negative value of h is usually still able to make negative , even if the entropy change is postive .
do worked examp,e o pae 70
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limitations of using g to predict feasibility of reactions
calculating the value of the free energy give a theoretical aanswer whether a reaction or process , will react spontaneously , wheher it is nthemoynmically possible .
if a reaction is found to have a negative value of g , what does this mean
does not mean it will actually go on to react ., for example burning petrol , it is aa very exothermic reaction , and produce gaseous products , hence an increase in entropy . thermodynamically it should .
how does whether a reaction proceed spontaneously or not depend on kinetic factors
- the reaction may have a hight activation energy - energy needs to be initially supplied to overcome this .
-the rate of reaction is extremely slow .
reactions that have positive values are considered not feasible .
they can be made to take place however , usually by changing the temperature of the reactionm .
what is oxidation
loss of electrons , or an increase in oxidation number .
what is reduction
reduction is the gain of electrons or aq decrease inm oxidation number .
what is an oxidising agent
species that is reduced in a reaciton and causes another speices to be idised
