Chemistry 2720 Fall 1998 Test 1

1. Do you expect to be positive or negative for the reaction

   

   Explain briefly. [5 marks]

2. Compare the enthalpy of combustion of glucose at to the enthalpy of combustion at . In your opinion, is the difference sufficiently small to ignore in metabolic calculations? [10 marks]
3. Catalytic hydrogenation converts unsaturated hydrocarbons into saturated hydrocarbons by reaction with hydrogen gas. How much heat is produced or absorbed per mole of ethene ( ) hydrogenated to ethane ( ) in a constant-volume reactor at 298K? Indicate clearly whether heat is absorbed or produced. [10 marks]
4. Calculate the entropy of water vapor at and 1atm. The entropy of liquid water at and 1atm is . The constant-pressure specific heat capacity of liquid water is and the heat capacity of water vapor is . The enthalpy of vaporization of water at and 1atm is 40.66kJ/mol. [10 marks]  
5. Using your knowledge of thermodynamics, prove that steam at will condense in a room at . Question 4 contains relevant data. [5 marks]
6. A condenser is a device which puts a vapor in thermal contact with a substance (often water) which can absorb heat and therefore cause the vapor to condense. Here is a simple diagram of a condenser:

   

   Water (from a tap) flows through the outer jacket. The vapor condenses on the walls and then drips out of the device.

   1. In a small still, 1L of liquid ethanol is produced per hour. The ethanol is not cooled appreciably below its boiling point before entering the collection vessel. How much heat is gained by the condenser water during an hour? Ethanol boils at C and its enthalpy of vaporization is 878.60J/g. The density of ethanol is 0.79g/mL. [5 marks]
   2. The tap water enters the condenser at a temperature of C and flows through the condenser at a rate of 20L/h. The density of water is approximately constant and is 0.999g/mL. For water, . At what temperature is the water leaving the condenser? [5 marks]

Formulas and data

To convert degrees Celcius to Kelvin, add 273.15.