Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

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

The relation between the magnitudes of lattice energy of crystal and its formation energy is:

  1. lattice energy > formation energy
  2. lattice energy $=$ formation energy

  3. lattice energy < formation energy

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lattice energy is the energy required to break apart an ionic solid and convert its component atoms into gaseous ions. The value of the lattice energy to always be positive.

Also, enthalpy of lattice formation is defined as the energy released when gaseous ions bind to form an ionic solid. The value is negative but has the same magnitude as lattice energy.
Hence, $B$ is correct.

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

If $Na^+$ ion is larger than $Mg^{2+}$ ion, and $S ^{2-}$ion is larger than $Cl^{-}$ ion, which of the following will be less soluble in water?

  1. $NaCl$
  2. $Na _{2}S$
  3. $MgCl _{2}$
  4. $MgS$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The lattice energy of a salt  gives a rough indication of the solubility of the salt in water because it reflects the energy needed to separate the positive and negative ions in a salt. Sodium and potassium salts are soluble in water because they have relatively small lattice energies. Magnesium and aluminum salts are often much less soluble because it takes more energy to separate the positive and negative ions in these salts.

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

Which of the following has higher lattice energy -$Al _2O _3$ or $Al _2Se _3$?

  1. $Al _2O _3$ > $Al _2Se _3$
  2. $Al _2O _3$ < $Al _2Se _3$
  3. $Al _2O _3$ = $Al _2Se _3$

  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. The two species have the same charge but the size of $Se$ is greater than $O$. Hence lattoce energy of $Al _2O _3$ is greater than $Al _3Se _3$.

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.