6 Questions Chemistry Homework


1. The methane, CH4(g) reaction and associated thermodynamic data at 298 K are given below.


CH(g) + 2 O2 (g)CO2 (g) + 2 H2O (l)

DGorxn= - 818kJ/mol

DHorxn= - 890kJ/mol

DSorxn= - 242 J/molK


Suppose that you start with 1 atm CH4, 0.2 atm O2, and 0.00038 atm CO2. How does the maximum non-expansion work compare with standard conditions? Provide a thermodynamic justification to your answer.


2. Solid Ni metal (melting point 1728 K) has the amazing ability to react with gaseous carbon monoxide, CO(g), at 323 K to form a volatile, colorless liquid, Ni(CO)4 (boiling point 316 K). Ludwig Mond - the person who made this discovery-described the reaction as 'giving wings to the metal'.


Ni (s)+4 CO (g)Ni(CO)4(g) DHorxn= -161 kJ/mol

Given that DSOrxn = -410 J/molK, calculate the value of DGOrxn at 25OC.


3. Considering the data above, and given that for the process Ni(s)Ni(g) DHOvap = +430 kJ/mol, determine the bond enthalpy for a Ni--CO bond.


4. Suppose that you place 1 atm of Ni(CO)4(g) in a closed container with a trace amount of CO (PCO=0.002 atm) at 25OC and allow it to reach equilibrium. What changes, if any, do you expect to observe when the reaction mixture is allowed to reach equilibrium? Explain your reasoning.


5. Mond developed a practical two-step separation scheme to obtain pure nickel metal from a mixture of nickel with other metals that do not undergo the same reaction, using only carbon monoxide. If the first step involves formation of pure gaseous Ni(CO)4 from the mixture, based on the thermodynamic data above, what do you think might be the final step to obtain pure Ni metal? Use a thermodynamic argument to justify your answer.


6. Consider the evaporation of water at 298 K and 1 atm pressure, H2O(l) -> H2O(g). The standard free

energy of this reaction is: DGOrxn = +8.6 KJ/mol. If the partial pressure of water in the air on a dry (non-humid) day at 298 K is 0.001 atm, calculate DGrxn and state whether the above process (i.e. evaporation of water) would proceed spontaneously. Show how you arrived at your answer.

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