Tag: chemistry

Questions Related to chemistry

Select the correct order of lattice energy.

  1. $LiF\, <\, LiBr\, <\, LiI$

  2. $LiCl\, >\, LiBr\, >\, LiI$

  3. $LiCl\, >\, NaCl\, >\, KCl$

  4. $BeCO _3\, <\, MgCO _3\, <\, SrCO _3\, <\, BaCO _3$


Correct Option: B,C
Explanation:

The lattice energy decreases in the order $LiCl\, >\, LiBr\, >\, LiI$. 

As the size of the anion increases from chloride to iodide, the lattice energy decreases.
The lattice energy decreases in the order $LiCl\, >\, NaCl\, >\, KCl$. 
As the size of the cation increases from lithium to potassium, the lattice energy decreases.

Lattice energy of ionic compounds depend upon:

  1. packing of ions only

  2. charge and size of ions

  3. charge on ion only

  4. size of ions only


Correct Option: B
Explanation:

Lattice energy is defined as the heat of formation for ions of opposite charge in the gas phase to combine into an ionic solid. It is directly proportional to the charge on the ions and inversely proportional to the size of the ions. 

Which of the following compounds will have the largest lattice energy?

  1. $AlBr _3$

  2. $CaO$

  3. $LiBr$

  4. $MgBr _2$


Correct Option: A
Explanation:

Among the cations, $Al^{3+},\ Ca^{2+},\ Li^{+}$ and $Mg^{2+}$, $Al^{3+}$ has the highest charge. Hence, $AlBr _3$ has the highest lattice energy. The lattice energy is directly proportional to the charge on the ion and inversely proportional to the size of the ion. 

The lattice energies of the oxidies of $Mg,Ca,Sr \;$ and $\;Ba$ follow the order:

  1. $BaO\;>\;SrO\;>\;CaO\;>MgO$

  2. $CaO\;>\;BaO\;>\;SrO\;>\;MgO$

  3. $MgO\;>\;SrO\;>\;CaO\;>\;BaO$

  4. $MgO\;>\;CaO\;>\;SrO\;>\;BaO$

Correct Option: D

The order of increasing lattice energy of the following compounds is :

  1. $NaCl\;<\;CaO\;<\;NaBr\;<\;BaO$

  2. $NaBr\;<\;NaCl\;<\;BaO\;<\;CaO$

  3. $NaCl\;<\;NaBr\;<\;BaO\;<\;CaO$

  4. $NaBr\;<\;NaCl\;<\;CaO\;<\;BaO$


Correct Option: B

From the following sequence calculate the lattice energy of AB(s):
$A(s)\rightarrow A(g)+e$;      $610\;kJ\;mol^{-1}$
$B(g)+e\rightarrow B(g);$      $-260\;kJ\;mol^{-1}$
$A(s)+B(g)\rightarrow AB(s);$      $-569\;kJ\;mol^{-1}$

  1. $-219$

  2. $-919$

  3. $+1539$

  4. $+301$


Correct Option: B
Explanation:
The lattice energy of a crystalline solid is usually defined as the energy of formation of the crystal from infinitely-separated ions, molecules, or atoms. 
let the equations be 1, 2 and 3.
We will get the lattice energy by  $3-2-1 $= $-569+260-610$ $= -919$

The lattice energies of $KF,KCl,KBr \;$ and $\;KI$ follows the order:

  1. $KF>KCl>KBr>KI$

  2. $KI>KBr>KCL>KF$

  3. $KF>KCl>KI>Br$

  4. $KI>KBr>KF>KCl$


Correct Option: A
Explanation:

Lattice energy is directly proportional to the charge of the ions and inversely proportional to the size of the ions. Thus lattice energy increases as the size of anion decreases. 

Strength of ionic bond depends on lattice energy.

  1. True

  2. False


Correct Option: B
Explanation:

Bond strength mostly depends on the charges present on each ion and the distance between them.Small, highly charged ions will form stronger bonds while large,minimally charged ions will form weaker bonds.

Identify the correct order of lattice energies.

  1. $CsCl < RbCl < KCl < NaCl$

  2. $KCl > CaCl _2 > AlCl _3$

  3. $NaCl < LiCl < MgCl _2 < AlCl _3$

  4. $LiCl > NaCl < MgCl _2 < AlCl _3$


Correct Option: A
Explanation:
$I^{st}$ group elements lattice energy is inversly proportional to radius and directly proportional to charge.
According to question all compounds have same charge but radius differs.
The order of radius is $Cs>Rb>K>Na$ 
So order of lattice energy is $CsCl<RbCl<KCl<NaCl$

The lattice energy of four ionic compounds $W, X, Y,$ and $Z$ are measured. The energies are found to be $-922\ kJ/mol, -769\ kJ/mol, -718\ kJ/ mol,$ and $-688\ kJ/mol$ respectively.
The four ionic, compounds are $NaCl, NaF, KBr$, and $KCl$.
Which of these ionic compounds could be identified as compound X based on the lattice energy?

  1. $NaCl$

  2. $NaF$

  3. $KBr$

  4. $KCl$


Correct Option: A