Chemistry 2720 Fall 1999 Test 1

Answer all questions. Note that useful information (data, equations) is given at the end of this paper.

Aids allowed: calculator.

1. State whether each of the following statements is true or false. Explain briefly (one sentence or so) what is wrong with each of the false statements. [10 marks]
   1. The first law forbids the melting of ice below at atmospheric pressure.
   2. Since E is a state function, then for any process which returns the system to its original state (a cyclic process) .
   3. If for a reaction at constant temperature and pressure is negative, the reaction is spontaneous.
   4. The second law limits the efficiency of the conversion of heat into work but does not limit the conversion of work into heat.
   5. The enthalpy of formation of an aqueous hydrogen ion is a measurable quantity.
   6. The entropy of the universe never decreases.
   7. If for a reaction is negative, the reaction is not spontaneous.
2. Prove that . [5 marks]
3. In a bomb calorimeter, a substance is completely burned in a large excess of oxygen at constant volume. It is very important that the amount of sample used be carefully limited since the heat from the reaction warms the oxygen, which increases the pressure in the bomb. The combustion energy of coal is approximately -25kJ/g. If the maximum safe temperature rise in a given calorimeter is approximately 6K and the constant-volume heat capacity of the device is 10kJ/K, what is the maximum permissible sample size? [5 marks]
4. 1. Calculate the work done per mole when an ideal gas is expanded reversibly by a factor of 2 at . [7 marks]
   2. A friend thinking of investing in a company which makes engines shows you the company's prospectus. Analyzing the machine, you realize that it works by harnessing the expansion of a gas. The machine's operating temperature is approximately constant at and the gas doubles in volume during the power extraction phase of operation. A quick calculation shows that the machine is claimed to produce about 3.5kJ/mol of work during the expansion. What advice would you give your friend? Give a brief thermodynamic rationale. [3 marks]
5. At , the enthalpy of reaction for

   

   is . The specific heat capacity of carbon monoxide is . Accurately calculate the standard enthalpy of formation of carbon monoxide (at ). [10 marks]

6. Potassium melts at 336.4K with an enthalpy of melting of 2.333kJ/mol. The specific heat capacity of the solid from 298.15K to the melting temperature is approximately constant at . The specific heat capacity of the liquid is given by the formula

   

   where is in and T is in Kelvin. The entropy of solid potassium at 298.15K is . What is the entropy of liquid potassium at 1000K? [10 marks]

Useful information

To convert degrees Celsius to Kelvin, add 273.15.

Standard thermodynamic data