Module 5 : Electrochemistry
Lecture 21 : Review Of Thermodynamics
  21.15  
Problems
21.1)
For 2 moles of a monatomic ideal gas, at 297.35 K and 1 atm, what is the volume of the system? For this fixed volume, if the temperature is doubled, what is the change in p, U and H? What are the values of q and w for this process? If this system is now compressed to half its volume at the constant system pressure, what is the work done on the system, U and H? What is q for this process? In this state, the system has a temperature of 297.35 K. Now, the system undergoes an isothermal reversible expansion until it reaches the starting volume. Calculate w and q for this third step of this cycle. Represent this cyclic process on PV, VT and pT diagrams and calculate the changes in w, q, U and H for the cyclic process. For a constant volume process, U =C V dT and for constant pressure process, H = CP dT. If U is known, H can be calculated as H =U + (PV)
   
21.2) The heat capacity of water CP is 18 cal/(deg mol). What is the enthalpy change of water when it is heated from 25oC to 100o C? Assume CP to be independent of temperature and use H = CP(T2 -T1). For the process H2 O(l) H 2 O(s), H (0 o C) = -1436 cal/mol. What is H for this process at –10o C? For ice, CP = 9 cal/(deg mol). Use the Kirchoffs equation H (T 2 ) = H(T 1 ) + T1T2 CP dT. In this problem, assume CP and CP to be independent of temperature.
   
21.3)

The heat capacities of many substances can be expressed as CP = a + bT + cT -2 in the temperature range of 298 K to 2000 K. For CH 4 , the values of the coefficients are a = 5.65, b = 11.44 x 10 -3 and c = -7.0 x 10 5 . The units (of CP ) are in cal/deg/mol. For CH 4 , what is H between 300 K and 1500 K? What would be H if C was assumed to be a constant = 5.65 cal/(deg mol) in this temperature range?
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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