Lattice Energy

Lattice Energy is the energy required to combine gaseous ions into a solid, crystalline structure. 

Examining Lattice Energy

Concept: Understanding Exergonic & Endergonic Reactions 

1m
Video Transcript

Remember we said anytime we're forming a bond, it's described as a certain process. Every time we're making bonds, we're releasing energy. Every time we're releasing energy, it's an exergonic process. Exergonic processes form bonds are releasing energy. If that energy happens to be in the form of heat, then they get the name exothermic. Both are really saying the same thing. Exergonic is just the common thing for all forms of energy. Exothermic is if that particular energy originates as heat.

When dealing with the absorbing or releasing of energy in general then we use the terms endergonic & exergonic

Concept: Understanding Lattice Energy

3m
Video Transcript

We're going to say here lattice energy is the enthalpy change that occurs when one mole of ionic solid separates into its ions. We're going to say it tells us the strength of ionic interactions and has an influence on a lot of features – melting point, hardness, solubility, boiling point, freezing point.
A good example of lattice energy, the formula that we use for it, a good example would just be Li+ gaseous phase with F- gaseous phase combining to give us LiF solid. We're going to say here delta H would be 1050 kilojoules per mole. The lattice energy needed to break up lithium fluoride would be that much. This is how much energy would be required of us to break up lithium fluoride.
We're going to say here the formula for lattice energy or ionic bond energy can be broken down as this. We're going to say it equals the cation charge times the anion charge in absolute brackets. Because it’s absolute, we know that the anion charge will be negative, the cation charge will be positive. A negative times a positive gives me a negative answer. But because it's in absolute brackets, the answer overall will be positive. That's going to be divided by the cation radius plus the anion radius.
What do I mean by radius? I mean period number. I'm breaking down lattice energy in a much, much simpler way than your book or your professor normally would. In your book, it gives you a much complicated larger formula in order to figure out who has the largest lattice energy. You don’t really need to use that larger formula. You just need to focus on the fundamentals. This equation just breaks off all the complex part of the equation and gives you the most important part that you need to know. When it comes to lattice energy, you can use this basic form of the equation to always get the right answer.

Example: For each pair, choose the compound with the lower lattice energy.

a. BaO or MgO

b. LiCl  or  CaS

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Problem: Choose the compound with the lower lattice energy.

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Problem: Choose the compound with the higher lattice energy.

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Lattice Energy Additional Practice Problems

Which has the larger ΔHhydr in each pair of Problem 13.32?

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What is the charge density of an ion, and what two properties of an ion affect it?

(b) Arrange the following in order of increasing charge density:

(c) How do the two properties in part (a) affect the ionic heat of hydration, ΔHhydr?

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Aluminum oxide (A12O3) is a widely used industrial abrasive (emery, corundum), for which the specific application depends on the hardness of the crystal. What does this hardness imply about the magnitude of the lattice energy? Would you have predicted from the chemical formula that A12O3 is hard? Explain.

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For each pair, choose the compound with the lower lattice energy, and explain your choice:

(a) NaF or NaCl

(b) K2O or K2S

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For each pair, choose the compound with the lower lattice energy, and explain your choice:

(a) CaS or BaS;

(b) NaF or MgO.

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(a) In general, how does the lattice energy of an ionic compound depend on the charges and sizes of the ions?

(b) Ion arrangements of three general salts are represented below. Rank them in order of increasing lattice energy.

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Rank the following ionic compounds by the magnitude of their lattice energy. Rank from highest to lowest magnitude of lattice energy.

LiCl, MgO, Na2O, BeO, Na2O

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Rank the compounds in order of decreasing magnitude of lattice energy. From Largest to Smallest

BaO, KCl, CaO, RbBr

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A) Arrange the following substances in order of decreasing magnitude of lattice energy.

CaO, NaF, SrO, KCl

Rank from largest to smallest magnitude of lattice energy.

B) Draw each molecule with their atoms and bonds

NF3, HBr, SBr2, CCl4

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Use the following information to calculate the ΔH° lattice of MgF2:

Mg(s) → Mg(g)                     ΔH° =148 kJ

F2(g) → 2F(g)                       ΔH° =159 kJ

Mg(g) → Mg(g)+e-              ΔH° =738 kJ

Mg+(g) → Mg2+ (g)+e-          ΔH° =1450 kJ

F(g)+e- → F-(g)                     ΔH° =-328 kJ

Mg(s) +F2(g) → MgF2 (s)      ΔH° =-1123 kJ

_______ kJ

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Consider the following ionic substances and arrange them in order of decreasing lattice energy.

MgCl2            CaCl 2            MgF 2

A.  MgF2>CaCl2>MgCl2 

B. MgF2>MgCl2>CaCl2

C. MgCl2>CaCl2>MgF2

D. CaCl2>MgF2>MgCl2

E. CaCl2>MgCl2>MgF2

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Which of the following has the highest melting point?

  1. RbF
  2. KI
  3. KF
  4. KBr
  5. KCl
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Which of the following has the highest lattice energy?

  1. NaCl
  2. KI
  3. MgO
  4. BaO
  5. CaO
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The solubilities of NaF and NaCl in water at 25°C are approximately 360 g/L H 2O and 80 g/L H2O respectively. Based on this information, which compound do you think has the larger lattice energy? 

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If the following crystallize in the same type of structure, which has the highest lattice energy?

1. KF

2. KBr

3. KCl

4. LiF

5. LiCl

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The lattice energy of calcium bromide is the energy change for the reaction

1. CaBr2(s) → Ca(g) + 2 Br(g)

2. Ca(s) + Br2(ℓ) → CaBr 2(s)

3. Ca(g) + 2 Br(g) → CaBr 2(g)

4. CaBr2(s) → Ca2+(g) + 2 Br(g)

5. CaBr2(s) → Ca(g) + Br 2(g)

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Which of the following reactions is associated with the  lattice energy of Li2O (ΔH°latt)?

a) Li2O (s)  →  2 Li+ (g) + O2- (g)

b) 2 Li+ (aq) + O2- (aq)  →   Li2O (s)

c) 2 Li+ (g) + O2- (g) →    Li2O (s)

d) Li2O (s) →   2 Li+ (aq) +  O2- (aq)

e) 2 Li (s) + O2 (g) →  Li2O (s)

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Choose the compound below that should have the highest melting or boiling point according to the ionic bonding model.

AIN                                   MgO                                   NaF     

 

 

 

 

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Which metal has the lowest melting point?

a) Li

b) Na

c) K

d) Rb

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Which of the following ionic bonds will have the greatest attraction?

A. BeCl2

B. MgCl2

C. SrCl2

D. BaCl2

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Which is a FALSE statement?

(A) The lattice energy of LiCl has a larger magnitude than that of NaCl.

(B) The lattice energy of CaO has a larger magnitude than that of NaCl.

(C) Na reacts with 1/2 Cl 2 to form NaCl molecules

(D) Some ionic compounds may not conduct electricity when dissolved in water.

(E) Lattice energy decreases as ionic radius increases as long as charge remains constant.

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Rank this series of ionic compounds from smallest to  largest magnitude (most exothermic) lattice energy:  

NaCl         MgO        CaO       Al  2O3  

a. NaCl < CaO < MgO < Al 2O3

b. CaO < NaCl < MgO < Al 2O3

c. Al2O3 < CaO < NaCl < MgO

d. CaO < NaCl < Al 2O3 < MgO

e. Al2O3 < NaCl < CaO < MgO 

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The lattice energy for ionic crystals decreases as the charge on the ions _____________ and the size of the ions __________________. 

(a) increases, increases

(b) increases, decreases

(c) decreases, increases

(d) decreases, decreases

(e) None of these choices are correct.

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Which of the following compounds would be expected to have the greatest lattice energy?

a) SrO

b) CsI

c) NaBr

d) MgO

e) BaS

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Which of the following solids would have the highest melting point?

1) NaI

2) NaF

3) MgO

4) MgCl2

5) KF

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The lattice enthalpy of calcium oxide is the energy change for the reaction

1. CaO(s) → Ca(g) + ½ O2(g)

2. Ca(g) + ½ O2(g) → CaO(s)

3. Ca(g) + O(g) → CaO(g)

4. CaO(s) → Ca2+(g) + O2- (g)

5. CaO(s) → Ca(g) + O(g)

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Which of the following would have the highest melting point?

1. KF

2. KBr

3. Kl

4. KCl

5. RbF

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Which of the following compounds is expected to have the strongest ionic bond?

a. MgO

b. KBr

c. NaI

d. SrO

e. CaS

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Which of the following substances has the least ionic character?

1. BeCl2

2. CaCl2

3. BaCl2

4. KCl

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Place the following in order of decreasing magnitude of lattice energy.

KCl        MgO       RbI

a. RbI > KCl > MgO

b. RbI > MgO > KCl

c. MgO > RbI > KCl

d. MgO > KCl > RbI 

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Which statement is a FALSE statement?

a. The lattice energy of LiCl has a larger magnitude than that of NaCl.

b. The lattice energy of CaO has a larger magnitude that that of NaCl.

c. Na reacts with ½ Cl 2 to form NaCl molecules.

d. Some ionic compounds may not conduct electricity when dissolved in water.

e. Lattice energy decreases as ionic radius increases as long as charge remains constant.

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Predict the reaction associated with lattice energy, ΔHlat of BaS.

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