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Intermolecular Forces
Changes of State
Colligative Properties
Reaction Rates
Reaction Mechanisms and Catalysis
100
Which type of intermolecular attractive force operates between: 1. all molecules 2. polar molecules
1. London dispersion force 2. dipole-dipole and London dispersion forces
100
Name the phase transition in each of the following situations and indicate whether the transition is exothermic or endothermic: 1. bromine vapor to bromine liquid 2. crystals of iodine disappear in the fume hood 3. rubbing alcohol from an open container disappears
1. condensation (exothermic) 2. sublimation (endothermic) 3. evaporation (endothermic)
100
List four properties of a solution that depend on the total concentration but not the type of particle(s) present as a solute.
freezing point depression, boiling point elevation, osmotic pressure, vapor pressure lowering
100
Define the term " reaction rate"
Reaction rate is the change in the amount of products or reactants in a given amount of time.
100
What is meant by the term elementary reaction?
An elementary reaction is a process that occurs in a single event; the order is given by the coefficients in the balanced equation for the reaction.
200
Describe the intermolecular forces that must be overcome to convert each of the following from a liquid to a gas: 1. Br2 2. CH3OH 3. H2S
1. London dispersion forces 2. hydrogen bonding, dipole-dipole, London dispersion 3. dipole-dipole, London dispersion
200
Explain why the heat of fusion of any substance is generally lower than its heat of vaporization.
Melting does not require separation of molecules, so the energy requirement is smaller than for vaporization, where the molecules must be completely separated.
200
Indicate the type of solute-solvent interaction that should be most important in each of the following solutions: 1. CCl4 in benzene 2. methanol in water 3. KBr in water 4. HCl in acetonitrile
1. dispersion 2. hydrogen bonding 3. ion-dipole 4. dipole-dipole
200
What are the four factors that can affect the rate of a chemical reaction?
concentration of reactants, surface area of reactants, and temperature, presence of a catalyst.
200
What is a reaction mechanism?
A reaction mechanism is a series of elementary reactions that describe how an overall reaction occurs and explain the experimentally determined rate law.
300
Define the term "polarizability"
Polarizability is the ease with which the charge distribution in a molecule can be distorted to produce a transient dipole.
300
What is the significance of the critical pressure of a substance?
The critical pressure is the pressure required to cause liquefaction at the critical temperature
300
List the following aqueous solutions in order of increasing boiling point: 1. 0.12M glucose 2. 0.05M LiBr 3. 0.05M Zn(NO3)2
0.05M LiBR, 0.12M glucose, 0.05M Zn(NO3)2
300
What factors determine whether a collision between two molecules will lead to a chemical reaction?
The energy of the collision and the orientation of the molecules when they collide.
300
What part of the energy profile of a reaction is affected by a catalyst?
A catalyst increases the rate of reaction by decreasing the activation energy (Ea) or by increasing the frequency factor (A).
400
Which member of the following pairs has the larger London dispersion forces? 1. H2O or H2S 2. CO2 or CO 3. CH4 or SiH4
1. H2S 2. CO2 3. SiH4
400
Explain how each of the following affects the vapor pressure of a liquid: 1. volume of the liquid 2. surface area 3. intermolecular attractive forces 4. temperature
1. no effect 2. no effect 3. vapor pressure decreases with increasing IMFs 4. increases with increasing temperature
400
What is the van't Hoff factor (i) for the following compounds: 1. CaCl2 2. NaCl 3. fructose
1. 3 2. 2 3. 1
400
According to the collision model, why does temperature affect the value of the rate constant?
At a higher temperature, there are more total collisions and each collision is more energetic.
400
Define an intermediate.
An intermediate is produced in one elementary step and is consumed in a later elementary step and therefore does not appear in the overall equation for the reaction.
500
Butane and 2-methylpropane have the same molecular formula but butane has a higher boiling point. Explain.
Both butane and 2-methylpropane experience London dispersion forces, however, the larger contact surface area between butane molecules facilitates stronger forces and produces a higher boiling point.
500
Define the critical point.
The critical point is the temperature and pressure beyond which the gas and liquid phases are indistinguishable.
500
Consider the general formula of carboxylic acids: CH3(CH2)nCOOH. How would you expect the solubility of these compounds in water and in hexane to change as n increases? Explain.
Solubility in water would decrease and the solubility in hexane would increase as n increases.
500
How do the half-lives of first-order and second-order reactions differ?
For first order reactions, the half-life depends solely on the reaction rate constant k. For second order reactions, the half-life depends on both the initial concentration and the rate constant.
500
Write the Arrhenius Equation
k = Ae^-(Ea/RT)