CHEM 122 Lecture Notes - Lecture 1: Lattice Energy, Ionic Compound, Reagent

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4 Mar 2017

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Polar molecules including ions: london dispersion forces, non polar molecules, hydrogen bonding, oxygen, nitrogen, uorine. Spontaneous process: a process that, once started, proceeds on its own without a continuous external in uence. The total energy of the universe remains constant (energy cannot be created nor destroyed: in a system, if heat is taken in, there will be a positive h and is therefore endothermic. This is also non-spontaneous (reactant favoured: in a system, if heat is being released, there will be a negative h and is therefore exothermic. This is spontaneous (product favoured: entropy (s): the amount of molecular randomness in a system, how can you change entropy, phase change, complexity of the molecule. The higher the mass the more random: mixing dissolving. This will increase entropy: reactions that increase the number of moles of a gas. If s is negative, it is non spontaneous. In general, a solute/solvent will mix if the intermolecular forces are similar.

Related Questions

Which of the following statements about intermolecular forces is(are) true?

a) London dispersion forces are the only type of forces that non-polar molecules exhibit

b) Molecules that have only London dispersion forces will always be gases at room temperature (25^oC)

c) The hydrogen bonding forces in NH₃ are stronger than those in H₂O

d) The molecules in SO₂ exhibit dipole-dipole intermolecular interactions

e) CH₃CH₂CH₃ has stronger London dispersion forces than does CH₄.

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* Circle the intermolecular force(s) that is/are present in each of the following species. [Hint: there may be more than one correct answer.]

Ar (hydrogen bonding, dipole-dipole forces, dispersion forces)

CH4 (hydrogen bonding, dipole-dipole forces, dispersion forces)

HBr (hydrogen bonding, dipole-dipole forces, dispersion forces)

HF (hydrogen bonding, dipole-dipole forces, dispersion forces)

CHCl3 (hydrogen bonding, dipole-dipole forces, dispersion forces)

* For the following pairs of atoms/molecules, circle the species that has the higher boiling point.

Ne or Xe

Cl2 or F2

HBr or HF

HCl or HI

H2O or H2S

* Phase changes always associate with change of enthalpy. For the following situations, name the phase

transition and indicate whether the process is exothermic or endothermic.

(a) Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:

(b) Water vapor turns to liquid water.

Answer:

(d) Iodine vapor turns to solid iodine.

Answer:

(e) Liquid helium turns to helium gas.

Answer:

* True or false

1. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

2. For molecules with similar size and molar mass, those with higher polarity would have higher boiling

point. Answer:

3. Ion-dipole forces exist between ionic potassium bromide and polar water.

Answer:

4. Dispersion forces exist between argon and helium. Answer:

5. Instantaneous dipoles exist in all molecules and atoms. Answer:

6. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

7. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

8. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

9. Viscosity decreases with increasing temperature. Answer:

10. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

D. 1. Silver chloride is not soluble in water. What are the relative strengths of the intermolecular forces between Ag and Ciions and water molecules as compared to the intermolecular forces between water molecules and the forces that hold the silver chloride as a solid? a. The ionic attractions are stronger than the polar covalent bonds between the H' and O ions of the b. The ionic attractions are weaker than the intermolecular forces between the Ag' and Cr ions and water c. The ionic attractions are stronger than the intermolecular forces between the Ag' and Cr ions and water d. The ionic attractions are the same as the intermolecular forces between the Ag and CI ions and water water molecules. molecules. molecules molecules 2. The value of AHsotn for a water soluble compound is +34 kJ moÄ¾1. Which value for this compound would be numerically larger, its lattice energy or its hydration energy? Select the single best answer. step. b. The lattice energy, because it is the endothermic step c. The hydration energy, because it is the exothermic step. d. The lattice energy, because it is the exothermic step. 3, which of the following are reasons why the value of ì¨,on for a gas such as CO2, dissolving in water, is negative? a. When a gas dissolves in a liquid, there is no endothermic step as with the lattice energy of a solid. b. When a gas dissolves in a liquid, there is only an exothermic step as with the lattice energy of a solid. c. The only enthalpy change is the one associated with hydration, and this is always positive. d. The only enthalpy change is the one associated with hydration, and this is always negative. e. When a gas dissolves in a liquid the lattice energy is always higher than the hydration energy, making the net enthalpy always negative. 4. Why is ammonia so much more soluble in water than is nitrogen? a. The triple bond in nitrogen prevents it from dissolving in water. b. Nitrogen has only London forces, while both water and ammonia form hydrogen bonds. c. The molar mass of nitrogen is much larger than the molar mass of ammonia, which reduces its solubility. d. Diatomic molecules are never soluble in water s which agueous solution, if either, is likely to have the highÏr boiling point 50 m Nal or en-Na e au

CHEM 122 Lecture Notes - Lecture 1: Lattice Energy, Ionic Compound, Reagent

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