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Unformatted text preview: valdez (vv689) Homework #3 Holcombe (52460) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An equilibrium in which processes occur con- tinuously, with NO NET change, is called 1. dynamic equilibrium. correct 2. homogeneous equilibrium. 3. hetergeneous equilibrium. 4. static equilibrium. Explanation: In dynamic equilibrium the forward and re- verse processes of the system continue but be- cause their rates are equal there is no change in the composition of the system. 002 10.0 points Which of the statements concerning equilib- rium is NOT true? 1. The value of the equilibrium constant for a given reaction is the same regardless of the direction from which equilibrium was attained. 2. A system moves spontaneously toward a state of equilibrium. 3. The equilibrium constant usually is inde- pendent of temperature. correct 4. Equilibrium in molecular systems is dy- namic, with two opposing processes balancing one another. 5. A system that is disturbed from an equi- librium condition responds in a manner to restore equilibrium. Explanation: Equilibrium constants are temperature de- pendent. 003 10.0 points Explain why equilibium constants are dimen- sionless. 1. They are dimensionless because concen- trations and pressures have no units. 2. They are dimensionless because the pres- sures or concentrations we put in are all for the substances in their standard states. 3. Every concentration or pressure that en- ters into K c or K p is really divided by the cor- responding concentration or pressure of the substance in its standard state. correct 4. The statement is not true. Equilibrium constants have units that involve some multi- ple of atmospheres or moles per liter. 5. They are not really dimensionless but we must treat them as such in order to be able to take ln K in the expression G =- RT ln K . Explanation: The amount of each component is in terms of activity, which is the measured amount (concentration, pressure) divided by the amount of that component in its standard state in that unit. The units in the numera- tor and denominator are identical and cancel out....
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- Spring '09