For each of the following problems, a right answer is worth 3 points, a wrong answer results in -1 points and no answer is scored as a zero. You do not need to justify your answer.

1) During the adiabatic expansion of an ideal gas against atmospheric pressure, the internal energy will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

2) During the isothermal expansion of an ideal gas, the internal energy will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

3) During an exothermic chemical reaction inside a closed system the internal energy will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

4) The heat capacity at constant volume is ________ the heat capacity at constant pressure for an ideal gas:

  1. greater than
  2. less than
  3. the same as
  4. cannot determine

Answer

5) The value of q for an isothermal ideal gas system when work is being done on that system is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

6) The enthalpy change of a system at constant pressure when 1.00 J of heat is transferred into it is:

  1. 1 J
  2. -1.00 J
  3. 0 J
  4. 8.31 J

Answer

7) When molecules which are used as the refrigerant in your refrigerator condense or associate with each other, they will:

  1. Give off heat
  2. Take up heat
  3. Neither give off nor take up heat
  4. It depends on the temperature of the refrigerator.

Answer

8) The total entropy change for the spontaneous crystallization of sodium chloride from a water/ethanol solution is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

9) For a constant pressure system, if the entropy change for the surroundings is negative, then the process going on inside the system is:

  1. isothermal
  2. exothermic
  3. endothermic
  4. impossible to tell

Answer

10) When an open glass of water is cooled from 50 C to 20 C by putting the 50 C glass of water in a bath that is at 20 C, the entropy change of the glass of water is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

11) For the last problem (10) the absolute value of the entropy change in the bath is ___________ the absolute value of the entropy change in the glass of water:

  1. Greater than
  2. Less than
  3. The same as
  4. impossible to tell

Answer

12) At constant pressure and temperature, if the total entropy change for the system and surroundings during some process is positive then the free energy change for the process is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

13) The total entropy change for the reversible expansion of an ideal gas is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

14) When I dissolve salt in liquid water, the chemical potential of the water will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

15) At 0 C and 1 atm, the chemical potential of liquid water is ____________ the chemical potential of ice:

  1. greater than
  2. less than
  3. equal to
  4. impossible to tell

Answer

16) Exerting pressure on ice causes it to melt because the molar volume of ice is ____________ the molar volume of liquid water.

  1. greater than
  2. less than
  3. equal to
  4. impossible to tell

Answer

17) Adding salt to a mixture of ice and liquid water causes the temperature of the mixture to drop because:

  1. it stabilizes the ice phase
  2. it destabilizes the ice phase
  3. it stabilizes the water phase
  4. it destabilizes the water phase

Answer

18) A glass contains 1 mole of ice and 1 mole of liquid water at thermoequilibrium. After adding 1 Joule of heat to the system the temperature will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

19) The enthalpy change associated with mixing two different ideal gasses that start at the same temperature and pressure is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

20) If I add salt to water, the vapor pressure of the water will:

  1. increase
  2. decrease
  3. stay the same
  4. impossible to tell

Answer

21) In a system with 5 phases that coexist at equilibrium, what is the minimum number of components that must be present?

  1. 3
  2. 4
  3. 5
  4. cannot have 5 phases coexisting.

Answer

22) The reason why reactions come to an equilibrium point instead of going entirely to products is:

  1. The attractive and repulsive forces between molecules balance at exactly that point.
  2. The reaction is only endothermic at that point.
  3. The reaction is only exothermic at that point.
  4. The free energy change of mixing has a minimum when both reactant and product are present.

Answer

23) When a system is at equilibrium, the reaction free energy is:

  1. positive
  2. negative
  3. zero
  4. impossible to tell

Answer

24) For a reaction Aß à B with a standard reaction free energy of 1kJ/mole, the equilibrium constant is.

  1. greater than one
  2. one
  3. less than one
  4. impossible to tell

Answer

25) For the same reaction as in problem 24, the standard reaction enthalpy is:

  1. greater than zero
  2. zero
  3. less than zero
  4. impossible to tell

Answer

26) One finds that the equilibrium constant for a particular reaction increases with increasing temperature. Assuming that the standard reaction enthalpy and entropy are temperature independent, this means that:

  1. The standard reaction entropy is greater than zero
  2. The standard reaction entropy is less than zero
  3. The standard reaction enthalpy is greater than zero
  4. The standard reaction enthalpy is less than zero

Answer

27) At 20 C, the concentration of OH- is 10-4 M. What is the pH?

  1. 4
  2. 10-4 M
  3. 10-10M
  4. 10

Answer

28) In a 0.1 M solution of NaCl in water, you expect the activity of Na+ to

be _________ 0.1

  1. greater than
  2. less than
  3. equal to
  4. impossible to tell

Answer

29) For the elementary reaction, A+Bà C, the units of the forward rate constant are:

  1. S-1
  2. MS-1
  3. M-1S-1
  4. M-2S-1

Answer

30) The energy per photon of red light is __________ that of blue light.

  1. greater than
  2. less than
  3. equal to
  4. impossible to tell

Answer

31) The most common reason why an absorbance spectrum of a molecule at room temperature in solution has a width to it is:

  1. The uncertainty principle
  2. Light is not a single frequency -- it has some distribution of energies to it.
  3. Absorbance spectrophotometers are not perfectly accurate.
  4. Molecular motion in the ground and/or excited states.

Answer

32) The reason why metals are so shiny is:

  1. Their hardness makes them easy to polish.
  2. The electric field of the photon is forced to go to zero at the surface of the metal, generating a wave in the opposite direction.
  3. Because metals are so hard, photons undergo completely elastic collisions which gives them an equal and opposite momentum.
  4. Metals carry a large static charge at their surface that repels the photons.

Answer

33) Molecules generally fluoresce at wavelengths longer than they absorb because:

  1. Relaxation among vibrational levels in the ground and excited states usually results in loss of energy as heat.
  2. Fluorescence normally occurs in two or more emission steps, each one with a smaller energy than the original absorbance transition.
  3. Fluorescence occurs from triplet states that are at lower energy than singlet states.
  4. When the light bounces off a molecule it gives up some of its energy.

Answer

 

Each of the following numerical problems are worth 25 points. You must show your reasoning for credit.

34) For a reversible, isothermal expansion of 1 mole of an ideal gas from 5 liters to 10 liters at a temperature of 25 C, what is

a) the internal energy change?

b) enthalpy change for the system

c) work

d) heat

e) entropy change for the system

Answer

35) A container with 10 moles of liquid water initially at 25 C is cooled to -25 C ice at constant pressure. Calculate the

a) entropy change of the system

b) enthalpy change of the system

c) q for the process

Answer

36) The initial rate of B formation in the elementary reaction Aß à B is 0.10 M/s. The initial concentrations of A and B were [A0] = 1.00 M and [B0] = 0.00 M . The final concentration of A (after equilibration) is 0.20 M.

a) What is the equilibrium constant for this reaction?

b) What is the forward rate constant for this reaction?

c) What is the backward rate constant for this reaction?

Answer

37) There are a number of dye molecules whose absorbance changes radically with pH. Let's consider a dye that is a weak acid and only absorbs at 500 nm in the protonated form (AH + H2O ß à A- + H3O+, only AH absorbs light) . The dye has a pKA of 6.00 and the extinction coefficient of the dye at 500 nm is 5.00 x 103 M-1cm-1.

a) If the total concentration of the dye is 1.00 mM (i.e., [A-] + [AH] = 0.00100 M), what is the absorbance of the dye solution at pH 5.5 in a 1 cm cuvette at 500 nm?

b) If 1 microwatt (10-6 Joules/second) of 500 nm light entered the cuvette described above, how many photons per second would be transmitted through the cuvette?

Answer