Born Haber Cycle - Video Tutorials & Practice Problems
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In the Born-Haber Cycle, ionic solids are created through the ionization and eventual combination of elements.
The Born-Haber Cycle
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concept
Born Haber Cycle
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3m
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Now the Born Haber cycle is a reaction outline that gives the steps for the formation of an ionic compound from the standard states of its elements. So I know that's a mouthful. The Born Haber cycle is an extensive process. We're gonna go piece by piece, step by step to figure it out. Now recall first, a formation equation shows the standard states of elements combining to form 1 mole of product. Now remember, associated with the formation equation is our enthalpy or heat of formation, which is delta h f. Here, standard heat of formation has that little circle there. It's telling me here that the formation of 1 mole of sodium chloride is accomplished by combining 1 mole of sodium solid with half a mole of chlorine gas. Remember, in formation equations we can have fractions and decimals as coefficients. Now in order to calculate the enthalpy of formation, both elements must first be converted into their ionic gaseous forms. So we're starting out here with sodium solid, we're starting out here with c l 2 gas. What we need to do first is realize that we need to get sodium to its ionic form as a gas, and we need to get chlorine to its ionic form as a gas as well. To do that, I first have to convert sodium solid into a gas. Going from a solid to a gas is called sublimation. So we're dealing with enthalpy of sublimation. Once I have it in its gaseous state, I need to change it from a neutral metal to a positively charged metal. That means I'm removing electrons. Removing electrons has to do with ionization energy. And since I'm only removing 1 electron, it's ionization energy 1. If I needed to remove more than 1 electron, then I'd have to add an ionization 2, ionization 3, and so on. Remember, we talked about this under successive ionization energies. Next, here, I need to separate c l 2 into 2 separate chlorines, so I have to break the bond. This is called enthalpy of dissociation. Here, once we break the bond between the 2 chlorines, I just have 1 chlorine now as a gas, and then I have to add an electron to it. Adding an electron is electron affinity. And since I'm only adding 1 electron, it's e a 1. If I had to add more than 1 electron, there will be e a 2, e a 3, and so on. Now that I have both of them in their ionic forms, they're gonna combine together to give me my solid. Remember, combining gaseous ions to form a solid ionic product, this is connected to lattice energy. So it's a whole process. We have to do all of this just to get the enthalpy of formation. So I need to do step 1 which is enthalpy of sublimation. Step 2 would be ionization energy which could be in more than one step. Step 3, I have to do enthalpy of dissociation to break a bond so I can get a single chlorine. Then I need to make it negative so I have to do electron affinity, which also could be more than one step. Once I get them into their ionic gas form, then I have lattice energy to complete it. So you can say that enthalpy of formation is composed of these 5 fundamental steps. So like I told you, the Born Haber Cycle has a lot of parts to it, but just remember the method we used here to justify how sodium combines with chlorine to give us sodium chloride.
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example
Born Haber Cycle Example 1
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1m
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Here it says, when setting up the steps of the Bornhaven cycle for potassium oxide, how many ionization energies, I e, how many electron affinities e a do you need? Remember, we have to get them into their ionic forms. Right? And we need 2 potassium ions as gas to combine with 1 oxide ion as a gas. Then they will combine to give me potassium oxide solid. Realize here that we need oxygen to get a 2 minus charge. So we're not adding 1 electron, we're adding 2 electrons. That means that we're gonna need to do 2 electron affinities. So we need 2 electron affinities, which means this is out, this is out, and this is out. And then finally, what else do we need? Well, we have 1 potassium solid initially, but at the end we're gonna need 2 potassiums. So we're gonna have to do ionization energy twice, one for each of the potassium solids. And then both of them would then undergo oops. We'll have them as gases actually, and then each one will have its electron plucked off. So we need to do 2 ionization energies, one for each Potassium as a neutral gas. So we need to do 2 electron affinities and 2 ionization energies giving us e as our final answer.
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Problem
Problem
Using the Born-Haber Cycle, demonstrate the formation of cesium chloride, CsCl, and calculate its enthalpy of formation.
A
-433 kJ/mol
B
-354 kJ/mol
C
589 kJ/mol
D
498 kJ/mol
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Problem
Problem
Calculate the lattice energy for the following formation equation:
A
-891 kJ/mol
B
-598 kJ/mol
C
-1049 kJ/mol
D
-2098 kJ/mol
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