Tag: energy cycles

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Questions Related to energy cycles

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

Which has larger lattice energy among $ZnO$ and $NaCl$?

  1. $ZnO$ > $NaCl$
  2. $ZnO$ < $NaCl$
  3. $ZnO$ = $NaCl$

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Lattice Energy is directly proportional to the charge on the ions and inversely proportional to the size of the ions. There are two factors at work here. The main factor is the charge on the ions. In $ZnO$, both positive and negative ions carry two charges. In $NaCl$, they only carry one. The lattice energy is much greater in $ZnO$ than in $NaCl$.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

The addition of energy in the form of heat causes molecules or crystals of the substance to break up into ions.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The breaking up of a compound into simpler constituents that are usually capable of recombining under other conditions. In electrolytic, or ionic, dissociation, the addition of a solvent or of energy in the form of heat causes molecules or crystals of the substance to break up into ions (electrically charged particles).

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

Which shows the highest lattice energy?

  1. $RbF$
  2. $CsF$
  3. $NaF$
  4. $KF$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$NaF$  shows the highest lattice energy.Smaller the size of cation, more is attraction among ions. The bond between ions of opposite charge is strongest when the ions are small.The lattice energies for the alkali metal halides is therefore, largest.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

Based on lattice energy and other considerations which one of the following alkali metal chloride has the highest melting point ?

  1. $KCl$
  2. $RhCl$
  3. $LiCl$
  4. $NaCl$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Comparison of melting points of ionic compounds is generally done by considering the following two factors:

  1. Charge of the cation/anion  : More the charge of cation or anion, stronger will be the forces of attraction between the ions and higher will be the melting point.
  2. Ionic radii: More the distance between ions, lesser will be the strength of the bond giving rise to lesser melting point.                                              
Going by the above rules, the order should have been:
LiCl > NaCl > KC l> RbCl  
(Since charges of the ions are same for each molecule and cationic radius increases down the group.)
But $LiCl$, due to excessive polarization, exhibits high covalent character and is placed last in the order. Hence, the new order would be:
NaCl > KCl > RbCl > LiCl
The other ions, being similar in size to chloride ions, do not undergo much polarization.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

Select the correct order of lattice energy.

  1. $LiF\, <\, LiBr\, <\, LiI$
  2. $LiCl\, >\, LiBr\, >\, LiI$
  3. $LiCl\, >\, NaCl\, >\, KCl$
  4. $BeCO _3\, <\, MgCO _3\, <\, SrCO _3\, <\, BaCO _3$
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

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

  1. $AlBr _3$
  2. $CaO$
  3. $LiBr$
  4. $MgBr _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
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. 

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

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. $MgO\;>\;CaO\;>\;SrO\;>\;BaO$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For oxides of the same group (alkaline earth metals), the lattice energy decreases as the size of the cation increases. Since the ionic radii follow Mg2+ < Ca2+ < Sr2+ < Ba2+, the lattice energy follows MgO > CaO > SrO > BaO.

Multiple choice chemistry lattice energy defining lattice energy ionic or electrovalent bond energy cycles

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. $NaBr\;<\;NaCl\;<\;CaO\;<\;BaO$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lattice energy depends on charge and size. CaO and BaO (2+, 2-) have much higher lattice energies than NaCl and NaBr (1+, 1-). Within the pairs, smaller ions (Ca2+ vs Ba2+; Cl- vs Br-) lead to higher lattice energy, so the order is NaBr < NaCl < BaO < CaO.