Chemistry 2720 Spring 1998 Test 2

Aids allowed: calculator. Write your answers only in the booklets provided.

Answer exactly four questions of the following six questions. All questions are equally weighted. Any additional questions answered will not be marked.

1. is a radical which can dimerize to . What is the equilibrium ratio of to at 298K if rigid container is initially filled with 0.5atm of ? Treat both compounds as ideal gases.
2. Suppose that the Earth had a much lighter atmosphere, generating a surface pressure of 0.2atm. Could liquid water exist on Earth at this pressure? The normal boiling point of water is and the enthalpy of vaporization of water at this temperature is 40.66kJ/mol.

   Hint: Treat the enthalpy of vaporization as a constant.

3. 1. Relate S to a derivative of A.
   2. Derive a Maxwell's relation for , i.e. use the interchangeability of the order of differentiation to obtain this derivative.
   3. What is for an ideal gas?
4. A solution of NaOH is prepared. What is the pH of this solution at and at ?
5. Briefly explain each of the following concepts:
   1. coupled reactions
   2. Le Chatelier's principle
   Try to focus on the underlying thermodynamic principles. Illustrate your discussion with examples, if possible.
6. Suppose that a cell maintains its internal environment at a of 7.5 when the external medium has a of 5. This is achieved by the use of a proton pump powered by the hydrolysis of ATP:

   

   One ATP molecule is hydrolyzed for every two protons transported across the membrane. The standard free energy change for the hydrolysis at 298K in the biochemists' standard state is -31.0kJ/mol. The total concentration of phosphates within the cell is 2.8mmol/L. What is the minimum ratio of ATP to ADP in this cell?

Useful information

To convert degrees Celsius to Kelvin, add 273.

For an ideal gas, PV=nRT.