ChemBytes - Chapter 10

Answers

1. Calculate the enthalpy of formation of Ca(OH)₂(s) from the following data:

   H2(g) + 1/2 O2(g) H2O(liq)	DH = -68.3 kcal
   CaO(s) + H2O(liq) Ca(OH)2(s)	DH = -15.3 kcal
   Ca(s) + 1/2 O2(g) CaO(s)	DH = -151.8 kcal

   Ans: -235.4 kcal
2. Using available thermodynamic data from the chapter, calculate DH for each of the following reactions:
   Fe₂O₃(s) + 3 CO(g) 3 CO₂(g) + 2 Fe(s) Ans: -24.77 kJ
   2 NO₂(g) 2 NOg) + O₂(g) Ans: 114.14 kJ
   N(g) + NO(g) N₂(g) + O(g) Ans: -313.78 kJ
   
3. A sample of solid naphthalene, C₁₀H₈, weighing 0.600 gram is burned to CO₂(g) and H₂O(liq) in a constant volume calorimeter. In this experiment, the observed temperature rise of the calorimeter and its contents is 2.255°C. In a separate experiment, the total heat capacity of the calorimeter was found to be 2550 cal/°C. What is DE for the combustion of one mole of naphthalene? What is the DH for this reaction? By using the tabulated values for DH°_f(CO₂,g) and DH°_f(H₂O,liq), calculate the enthalpy of formation of naphthalene. DE = -5140 kJ/mol; DH_f (napthalene) = 60 kJ
4. One mole of an ideal gas at 300K expands isothermally and reversibly from 5 to 20 liters. Calculate the work done and the heat absorbed by the gas. What is DH for the process? DH = 0
5. Ethylene (C₂H₄) and propylene (C₃H₆) can be hydrogenated according to the reactions
   C₂H₄(g) + H₂(g) C₂H₆(g)
   C₃H₆(g) + H₂(g) C₂H₆(g) to yield ethane (C₂H₆) and propane (C₃H₆), respectively. From data available in the chapter, calculate DH for these reactions. What do these answers suggest about DH for reactions that are generally of the type C_nH_2n(g) + H₂(g) C_nH_2n+2(g) Ans: DH is roughly -130 kJ/mol