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# Problem Set 2

last edited by 10 years, 5 months ago

1) A sample consisting of 1.00 mol of the molecules in air is expanded isothermally at 25°C from 24.2 dm3 to 48.4 dm3 (a) reversibly, (b) against a constant external pressure equal to the final pressure of the gas, and (c) freely (against zero external pressure). For the three processes calculate q, w, ΔU, and ΔH.

2) A sample of oxygen of mass 96 g at 25.0 °C is allowed to expand reversibly and adiabatically from 5.00 dm3 to 10.00 dm3. What is the work done by the gas?

3) When 5.00 mol N2 is heated at a constant pressure of 3.00 atm, its temperature increases from 298 K to 345 K. Given that the molar heat capacity of N2 at constant pressure is 29.125 J K–1 mol–1, calculate q, ΔH, and ΔU.

4) The standard enthalpy of combustion of n-propane (C3H8) is –2220 kJ mol–1 at 25 °C. From this information and enthalpy of formation data for CO2(g) and H2O(g), calculate the enthalpy of formation of n-propane. The enthalpy of formation of propene (C3H6) is +20.42 kJ mol–1. Calculate the enthalpy of hydrogenation of propene to propane.

5)  Benzoic Acid (C6H5COOH) is a commonly used standard used for determining the calorimeter constant of a bomb calorimeter. The enthalpy of combustion for benzoic acid is very well known and is found to be  ΔcH =  -3227 kJ/mol. If a 0.596 g of benzoic acid is combusted in a bomb calorimeter and found to produce a 0.95 °C rise in temperature, calculate the calorimeter constant for the apparatus.

If 0.568 g of naphthalene (C10H8) is subsequently combusted in the bomb calorimeter at the same conditions, and produces a 1.56 °C rise in temperature, calculate the enthalpy of combustion of naphthalene.

6) A sample of nitrogen gas is adiabatically expanded such that its volume triples. If the sample initially is held 25 °C, what is the final temperature of the gas? Given that the initial pressure is 1 atm and the volume is 500 mL, calculate the work done.