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REVISION NOTES [print-friendly version]
Chapter 4.3 Intermolecular Forces and the Properties of Water
- Know the difference between intermolecular forces and intramolecular forces and be able to compare the strengths of covalent bonds within molecules to the various forms of intermolecular forces.
- Know the properties of covalent molecular substances - be able to identify covalent molecular substances from metallic, ionic and covalent network.
- Be able to define and explain the meaning of dispersion forces, dipole-dipole forces and Hydrogen bonding. *******
- Know which substances have intermolecular forces that are dispersion only.
- Be able to explain the trend in b. pts. and m.pts. down the group of halogens and noble gases, and also in the alkanes, alkenes and alcohols as the length of the carbon chain increases.
- Know the meaning of the terms dipole, polar bonds, polar molecule, non-polar molecule and electronegativity.
- Be able to predict the various shapes of common molecules - linear, bent, triangular planar, tetrahedral and triangular planar. Know the shapes of H2O, NH3, CH4, HCl, (From these be able to predict the shape of H2S, PH3, CF4, HF) Also know the shape of CO2.
- Be able to predict whether the molecules have a net dipole or not. Be able to identify in which substances dipole-dipole forces operate as well as dispersion.
- Be able to predict whether Hydrogen bonding operates between molecules of various substances.
- Be able to predict trends in physical properties like b. pt., m.pt., vapour pressure, heat of vapourisation, heat of fusion from the intermolecular forces. Or, from the physical properties, be able to predict the types of intermolecular forces that may be operating.
- Be aware that unless the numbers of protons and electrons in molecules are similar, you cannot make direct comparisons between the strength of dispersion forces compared to hydrogen bonding and dipole-dipole forces.
- Be able to explain some of the remarkable properties of water in terms of hydrogen bonding - density of water, viscosity, m.pt., b.pt, vapour pressure, heat of vapourisation and heat of fusion.
- Be able to explain why water expands (is less dense) when it freezes.
Chapter 4.4 - Solubility of Molecular substances in one another.
- Be able to predict the expected solubility of one molecular substance in another by comparing the types of intermolecular forces.
- Consider the resistance to separation of solute-solute molecules and the strength of the solute-solvent attractions.
- Remember substances dissolve in each other if resistance to separation from both the solute-solute and solvent-solvent attractions are low, or the strictions solute-solvent attractions are strong enough to overcome this attraction.
- Be able to explain and predict the solubility of combinations like non-polar solute - polar solvent e.g. I2 - water, polar solute - polar solvent e.g. methanol - water, polar solute - non-polar solvent e.g. water - petrol, non-polar solute - non-polar solvent e.g. I2 - petrol
- Be able to explain and predict the trends in solubilities of polar organic molecules as the carbon chain length increases. e.g. the solubilities of the primary alcohols in water and petrol.
- Be able to explain and predict the trends in solubilities of polar organic molecules as the number of hydroxyl groups increases. e.g. the solubilities of glycerol (propan-1,2,3-triol) compared to propanol in water and petrol and the solubility of glycol (ethan-1,2-diol) compared to ethanal in water and petrol.
- Be able to explain the meaning of the term ion-dipole forces, and energy of hydration.
- Be able to explain why many ionic solids are soluble in water but not in petrol.
- Be able to compare the relative energy required to separate the ions in their ionic lattice from the energy of hydration in exothermic and endothermic dissolutions.
Ch 28 - Equilibrium
- Be able to briefly explain some examples of physical equilibria e.g. water/water vapour equilibrium, water/molecular solid equilibrium, water/dissolved gas.
- Be able to write the equilibrium expression for K (Equilibrium Law) for any given equilibrium reaction. Be particularly aware of the special situations where a solid is present and where water is a reactant or product and also the solvent.
- Given values of concentrations be able to compare the product quotient (Q) with K to determine whether the system is at equilibrium or not. From that you should be able to predict which way the reaction will shift in order to achieve equilibrium.
- Be able to calculate K, given equilibrium concentrations at equilibrium.
- Be able to write the expression for Ksp (solubility product) of a saturated solution.
- Be able to calculate Ksp given the solubility of an ionic solid in water.
- Be able to calculate the solubility from the Ksp.
- Given Ksp, and the concentrations of the ions, be able to predict if a precipitate will occur or not. i.e. compare Q with K.
- Be able to state Le Chatelier’s Principle.
- Be able to predict the way a reaction will shift when a change is imposed on a system at equilibrium and explain this shift in terms of Le Chatelier’s Principle.
- if the concentration of one of the reactants is increased or decreased.
- if the partial pressure of one of the gases in a gaseous equilibrium is increased or decreased.
- if the total pressure is increased or decreased by changing the volume of a gaseous equilibrium.
- if the total pressure is increased by introducing another non-reacting gas to the system.
- if the temperature of the system is increased or decreased.
- Be able to draw graphs showing the changes imposed on a system at equilibrium and the effect of those changes.
- Be aware that the only change to equilibrium that affects K is temperature.
- Be able to predict if the value of K will increase or decrease with a temperature change.
- Be able to explain the other effect of increasing temperature - i.e. it also increases the rate of both the forward and back reactions.
- Be aware of the effect of a catalyst on a system at equilibrium - it also increases the rate of both the forward and back reactions; assists the system to reach equilibrium faster but does not favour the reactants or products.
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