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 A.S. Note: if you have not been given enough information to decide a sign, select the "unknown" option. reaction A B с observations This reaction is spontaneous only above 30. °C but proceeds at a slower rate below 199. °C. This reaction is spontaneous only below 19. °C. This reaction is exothermic and proceeds slower at temperatures below 60. °C. conclusions AH is AS is AH is AS is AH is AS is (pick one). (pick one) ✓ (pick one) ✓ (pick one) (pick one) (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 A.S. Note: if you have not been given enough information to decide a sign, select the "unknown" option. reaction A B с observations This reaction is spontaneous only above 30. °C but proceeds at a slower rate below 199. °C. This reaction is spontaneous only below 19. °C. This reaction is exothermic and proceeds slower at temperatures below 60. °C. conclusions AH is AS is AH is AS is AH is AS is (pick one). (pick one) ✓ (pick one) ✓ (pick one) (pick one) (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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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.
How does the second law of thermodynamics explain a spontaneous change in a system that becomes more ordered when that process is exothermic?
10.104 (a) When a chemical bond forms, what happens to the entropy of the system? (b) Thermodynamically, what allows any bond formation to occur? (c) What do your answers to parts (a) and (b) suggest must be true about the formation of chemical bonds for the octet rule to hold?
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?
Some water is placed in a coffee-cup calorimeter. When 1.0 g of an ionic solid is added, the temperature of the solution increases from 21.5C to 24.2C as the solid dissolves. For the dissolving process, what are the signs for Ssys, Ssurr, and Suniv?
Define the following: a. spontaneous process b. entropy c. positional probability d. system e. surroundings f. universe
One statement of the second law of thermodynamics is that heat cannot be turned completely into work. Another is that the entropy of the universe always increases. How are these two statements related?
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
Determine whether each of the following statements is true or false. (a) An exothermic reaction is spontaneous. (b) When G° is positive, the reaction cannot occur under any conditions. (c) S° is positive for a reaction in which there is an increase in the number of moles. d) If H° and S° are both negative, G° will be negative.
For the reaction at 298 K, 2NO2(g)N2O4(g) the values of H and S are 58.03 kJ and 176.6 J/K, respectively. What is the value of G at 298 K? Assuming that H and S do not depend on temperature, at what temperature is G = 0? Is G negative above or below this temperature?
What is the third law of thermodynamics? What are standard entropy values, S, and how are these S values (listed in Appendix 4) used to calculate S for a reaction? How would you use Hesss law to calculate S for a reaction? What does the superscript indicate? Predicting the sign of S for a reaction is an important skill to master. For a gas-phase reaction, what do you concentrate on to predict the sign of S? For a phase change, what do you concentrate on to predict the sign of S? That is, how are Ssolid, Sliquid, and Sgas related to one another? When a solute dissolves in water, what is usually the sign of S for this process?