            Main   Tutorials   Organic Chemistry   Practice Tests   Online Quizzes   Reference Tools   Spontaneity Practice Problems: Which has higher positional entropy? Gas H2O or Water H2O 100 atm  gas or 1 atm gas Calculate DSsurr for: (assume 1 atm and 298 K) Cgraphite (s) + O2 ----> CO2 (s)                      DH = -394 kJ SbO 6 (s) + 6C (s) ----> 4Sb (s)+ 6CO (g)       DH = 778 kJ Calculate DSo and DHo for the following reaction: (hint, use the thermodynamic data) Cl2 (aq) ---> Cl2 (g) Calculate what temperature the following reaction becomes spontaneous: Cl2 (aq) ---> Cl2 (g) Estimate DSo: 2C10H22(l) + 31O2 ----> 20CO2 + 22H2O HCl (g) + NH3(g) ----> NH4Cl(s) Calculate DG: N2(g) + 3H2 (g) <---> 2NH3 (g) PNH3 = 3.2 atm    PN2 = 4.0 atm   PH2 = 1.2 atm Answers: 1a.) Gas water has a higher positional entropy because under constant temperature and pressure, a gas takes more volume than a solid. The gas molecules, therefore, have more places they could be, which increases the positional entropy. 1b.) 1 atm. At lower pressure, there is an increase in volume (PV = nRT), and with an increase of volume, positional entropy increases. 2a.) DSsurr: -DH / T = -(-394/298) = 1.32 2b.) DSsurr: -DH / T = -(778/298) = -2.61 3.) DSo: 223-121 = 102 J/K*mol DHo: 0-(-231) = 23 kJ/mol 4.) DGo = DHo - TDSo 0 = 23000 - T(102) 230000 = T(102) T = 225 K At temperatures greater than 225 K, the reaction will be spontaneous. 5a.) DSo will be positive, because more gas is created. 5b.) DSo will be negative, because a solid is being formed from two gas molecules. 6.) Use the equation: DG = DGo + RT ln (Q). Q = (3.2)2 / ((1.2)3 * (4.0)) = 1.48 DG = -33300 + 8.3145 * 298 ln (1.48) DG = -32 kJ/mol news | about us | contact us tutorials index | organic chemistry | practice tests | online quizzes | reference tools site copyright (c) 2002-2013 Learn Chem   Subscribe to our low volume newsletter to receive up-to-date information about the CHEM SITE       