Chapter 13

# Chapter 13 - Physical Properties of Solutions A solution is...

This preview shows pages 1–11. Sign up to view the full content.

Physical Properties of Solutions

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount
Three types of interactions in the solution process: solvent-solvent interaction solute-solute interaction solvent - solute interaction H soln = H 1 + H 2 + H 3

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
solvent-solvent separation: ΔH solvent solute-solute separation: ΔH solute solvent-solute mixing: ΔH mix ΔH solvent + ΔH mix = ΔH solvation (For aqueous solutions, ΔH solvation = ΔH hydration ) So, for the following process: solute (undissolved) solute (dissolved) ΔH solution = ΔH solute + ΔH solvation/hydration
For ionic compounds dissolving in water: ΔH solution = – ΔH lattice + ΔH hydration (where ΔH lattice is always negative and ΔH hydration is always negative) This is just like Hess’s Law: ΔH° solution = ΣΔH° f (products) – ΣΔH° f (reactants) For example: ΔH° solution = ΣΔH° f (NaCl(aq)) – ΣΔH° f (NaCl(s)) for NaCl(s) NaCl(aq) (° = 1 molal (1m) aqueous solute)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
If ΔH latt of KBrO 3 = – 745 kJ/mol and the combined ΔH hyd = – 704 kJ/mol, what is the ΔH soln for the dissolution of KBrO 3 in water?
Answer: ΔH solution = – ΔH lattice + ΔH hydration = – (– 745 kJ/mol) + (– 704 kJ/mol) = + 41 kJ/mol But wait! If KBrO 3 dissolves readily in water (solubility = 6.9 g/100mL), then why is ΔH solution for KBrO 3 a positive value (endothermic process)?. ....................

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
If the ΔH solution is +, then endothermic; if ΔH solution is –, then exothermic. This contributes to the ENTHALPIC favorability of solution formation. But sometimes a solution has a + ΔH solution , but a solution still forms. Why? Entropy (S) – the natural tendency of most systems to become more disordered (disperse) – entropy tends to increase Solutions form naturally; pure solutes and solvents do not Solution Process involves TWO factors: 1) ΔH 2) ΔS The relative magnitudes of these factors determine whether a solution forms: the increase in S accompanying dissolution always favors solution formation, but ΔH can go either way to favor or not favor solution formation.
like dissolves like Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 ( l )

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Solubility of a solute = the maximum amount that dissolves in a fixed amount of a particular solvent at a specified temperature, given that excess solute is present NaCl: S = 39.12 g/100 mL H 2 O at 100°C AgCl: S = 0.0021 g/100 mL H 2 O at 100°C Why the difference? Depends on relative strength of IMF within and between solute and
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 07/15/2011 for the course CHEM 2045 taught by Professor Gower during the Spring '11 term at University of Florida.

### Page1 / 58

Chapter 13 - Physical Properties of Solutions A solution is...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online