Question

Rank the following solutes in order of increasing entropy when 0.0100 moles of each dissolve in 1.00 liter of water.

Answer 1

Answer:

The rank of the solutes in order of increasing entropy is:

•   CH₃OH < NaBr < CaCl₂ < Cr(NO₃)₃

Explanation:

Assuming temperature and other conditions are the same, you can qualititatively precict the relative increase of entropy, when a given amount of solute dissolves in a fixed aomount of water, by looking at the number of particles (molecules or ions) that are formed.

The particles of solute that, prior to get dissolved, are pure and orderly separated, will be very scattered after the dissolution, increasing, consequently, the degree of randomness or dissorder of the system.

Also, the greater the number of particles formed from each unit formula, the greater the degree of disorder and the greater the entropy.

Hence, being the entropy a measure of the radnomness of the system, you can predict that the greater the number of particles (molecules or ions) dissolved, the greater the entropy.

Now look at the dissociation of each given solute:

• CaCl₂ → Ca²⁺ + 2Cl⁻ : 3 ions are formed.

• CH₃OH: is a molecular compound, so 1 molecule is dispersed.

• Cr(NO₃)₃ → Cr³⁺ + 3 NO₃⁻: 4 ions are formed.

• NaBr → Na⁺ + Br⁻ : 2 ions are formed.

Then, the rank in order of increasing entropy, is:

       1       <     2   <     3     <      4

  CH₃OH < NaBr < CaCl₂ < Cr(NO₃)₃