Chapter 4 Homework Assignment Question 1 Classify the following phase changes by the signs of the system s H and S solid to liquid liquid to solid gas to solid solid to gas liquid to gas gas to liquid Question 2 Which of the following reactions have a positive Srxn Check all that apply 2A g 2B g 5C g 2A g B g C g A g 2B g 2C g A s B s C g Question 3 Calculate the standard entropy change for the following reaction at 25 C Question 4 Without referring to a data table rank the following compounds by standard molar entropy Highest S to Lowest S C H g N g H g Question 5 Consider the following reaction at 298 K Calculate the following quantities Question 6 For a particular reaction H 14 20 kJ and S 198 5 J K Calculate G for this reaction at 298 K What can be said about the spontaneity of the reaction at 298 K spontaneous in the reverse direction spontaneous as written Question 7 For the reaction described by the chemical equation a Use the data from the table to calculate the value of S rxn at 25 0 C b Calculate G rxn c In which direction is the reaction as written spontaneous at 25 C and standard pressure Question 8 Classify the possible combinations of signs for a reaction s H and S values by the resulting spontaneity Spontaneous as written at all temperatures Spontaneous in reverse at all temperatures Spontaneous as written above a certain temperature Spontaneous as written below a certain temperature Question 9 For a particular reaction H is 28 4 kJ and S is 87 9 J K Assuming these values change very little with temperature over what temperature range is the reaction spontaneous in the forward direction The reaction is spontaneous for temperatures T Question 10 The small bags of silica gel you often see in a new shoe box are placed there to control humidity Despite its name silica gel is a solid It is a chemically inert highly porous amorphous form of SiO2 Water vapor readily adsorbs onto the surface of silica gel so it acts as a desiccant Despite not knowing mechanistic details of the adsorption of water onto silica gel from the information provided you should be able to make an educated guess about the thermodynamic characteristics of the process Predict the signs of G H and S Question 11 Calculate the standard change in Gibbs free energy for the following reaction at 25 C Question 12 Under standard conditions 298 K and 1 atm which statement is true diamond converts to graphite spontaneously graphite converts to diamond spontaneously none of the above How can the spontaneity of the reaction be reversed increase the temperature decrease the temperature none of the above Question 13 Balance the equation and write the reaction quotient expression Qc Question 14 What is the value of K for this aqueous reaction at 298 K Question 15 At 25 C the equilibrium partial pressures for the following reaction were found to be PA 2 90 atm PB 2 20 atm PC 7 10 atm and PD 7 60 atm What is the standard change in Gibbs free energy of this reaction at 25 C Question 16 For a gaseous reaction standard conditions are 298 K and a partial pressure of 1 atm for all species For the reaction the standard change in Gibbs free energy is G 69 0 kJ mol What is G for this reaction at 298 K when the partial pressures are Question 17 A critical reaction in the production of energy to do work or drive chemical reactions in biological systems is the hydrolysis of adenosine triphosphate ATP to adenosine diphosphate ADP as described by for which G rxn 30 5 kJ mol at 37 0 C and pH 7 0 Calculate the value of Grxn in a biological cell in which ATP 5 0 mM ADP 0 30 mM and HPO42 5 0 mM Is the hydrolysis of ATP spontaneous under these conditions Question 18 The following equation represents the decomposition of a generic diatomic element in its standard state Assume that the standard molar Gibbs energy of formation of X g is 5 70 kJ mol 1 at 2000 K and 55 57 kJ mol 1 at 3000 K Determine the value of K the thermodynamic equilibrium constant at each temperature Assuming that H rxn is independent of temperature determine the value of H rxn from these data