Use the observations about each chemical reaction in the table below to decide the sign (positive or negative) of the reaction enthalpy AH and reaction entropy AS. Note: if you have not been given enough information to decide a sign, select the "unknown" option. reaction observations conclusions The reverse of this reaction is always spontangous but proceeds faster at temperatures above -20. "C. AN is Koick one) A AS is (pick one) This reaction is spontaneous only above -45. "C but proceeds ataslower rate AN is (pick one) below 146, "C. AS is (pick one) AN is (pck one) This reaction is faster above 26. "C than below. AS is (pick one)

Use the observations about each chemical reaction in the table below to decide the sign (positive or negative) of the reaction enthalpy AH and reaction entropy AS. Note: if you have not been given enough information to decide a sign, select the "unknown" option. reaction observations conclusions The reverse of this reaction is always spontangous but proceeds faster at temperatures above -20. "C. AN is Koick one) A AS is (pick one) This reaction is spontaneous only above -45. "C but proceeds ataslower rate AN is (pick one) below 146, "C. AS is (pick one) AN is (pck one) This reaction is faster above 26. "C than below. AS is (pick one)

Chemistry for Engineering Students

4th Edition

ISBN:9781337398909

Author:Lawrence S. Brown, Tom Holme

Publisher:Lawrence S. Brown, Tom Holme

Chapter10: Entropy And The Second Law Of Thermodynamics

Section: Chapter Questions

Problem 10.51PAE: 10.51 The combustion of acetylene was used in welder's torches for many years because it produces a...

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For the process A(l) A(g), which direction is favored by changes in energy probability? Positional probability? Explain your answers. If you wanted to favor the process as written, would you raise or lower the temperature of the system? Explain.
The reaction CO2(g)+H2(g)CO(g)+H2O(g) is not spontaneous at room temperature but becomes spontaneous at a much higher temperature. What can you conclude from this about the signs of H and S , assuming that the enthalpy and entropy changes are not greatly affected by the temperature change? Explain your reasoning.
Thermite reactions have been used for welding metal parts such as railway rails and in metal refining. One such thermite reaction is Fe2O3(s)+2Al(s)Al2O3(s)+2Fe(s). Is the reaction spontaneous at room temperature under standard conditions? During the reaction, the surroundings absorb 851.8 kJ/mol of heat.
Consider two processes: sublimation of I2(s) and melting of I2(s) (Note: the latter process can occur at the same temperature but somewhat higher pressure). I2(s)I2(g)I2(s)I2(l) Is S positive or negative in these processes? In which of the processes will the magnitude of the entropy change be greater?
What is the second law of thermodynamics? For any process, there are four possible sign combinations for Ssys and Ssurr. Which sign combination(s) always give a spontaneous process? Which sign combination(s) always give a non-spontaneous process? Which sign combination(s) may or may not give a spontaneous process?
Given that H f for HF(aq) is -320.1 kJ/mol and S for HF(aq) is 88.7 J/mol K, find Ka for HF at 25C.
For the reaction NO(g)+NO2(g)N2O3(g) , use tabulated thermodynamic data to calculate H and S. Then use those values to answer the following questions. (a) Is this reaction spontaneous at 25°C? Explain your answer. (b) If the reaction is not spontaneous at 25°C, will it become spontaneous at higher temperatures or lower temperatures? (c) To show that your prediction is accurate, choose a temperature that corresponds to your prediction in part (b) and calculate G . (Assume that both enthalpy and entropy are independent of temperature.)
What is the sign of the standard Gibbs free-energy change at low temperatures and at high temperatures for the formation of hydrogen sulfide from the elements? H2(g)+18S8(s)H2S(g)
10.51 The combustion of acetylene was used in welder's torches for many years because it produces a very hot flame: C2H2(g)+52O2(g)2CO2(g)+H2O(g) H= -1255.5 kJ (a) Use data in Appendix E to calculate S for this reaction, (b) Calculate G and show that the reaction is spontaneous at 25°C. (c) Ls there any temperature range in which this reaction is not spontaneous? (d) Do you think you could use Equation 10.4 to calculate such a temperature range reliably? Explain your answer.
Methane can be produced from CO and H2.The process might be done in two steps, as shown below, with each step carried out in a separate reaction vessel within the production plant. Reaction 1 CO(g)+2H2(g)CH3OH(l) S = -532 J/K Reaction 2 CH3OH(l)CH4(g)+12O2(g) S= +162 J/K NOTE: You should be able to work this problem without using any additional tabulated data. (a) Calculate H for reaction 1. (b) Calculate Gf for CO(g). (c) Calculate S° for O2(g). (d) At what temperatures is reaction 1 spontaneous? (e) Suggest a reason why these two steps would need to be carried out separately. Substance Hf (kJ mol-1) Gf (kJ mol-1) S (J mol-1 K-1) CO(s) -110.5 197.674 CH3OH( l ) -238.7 -166.4 126.8 CH4(g) -74.8 186.2
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Many plastic materials are organic polymers that contain carbon and hydrogen. The oxidation of these plastics in air to farm carbon dioxide and water is a spontaneous process; however, plastic materials tend to persist in the environment. Explain.