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- Enthalpy changes often help predict whether or not a process will be spontaneous. What type of reaction is more likely to be spontaneous: an exothermic or an endothermic one? Provide two examples that support your assertion and one counterexample.arrow_forwardThe formation of aluminum oxide from its elements is highly exothermic. If 2.70 g Al metal is burned in pure O2 to give A12O3, calculate how much thermal energy is evolved in the process (at constant pressure).arrow_forwardWhat is the sign of the standard Gibbs free-energy change at low temperatures and at high temperatures for the explosive decomposition of TNT? Use your knowledge of TNT and the chemical equation, particularly the phases, to answer this question. (Thermodynamic data for TNT are not in Appendix G.) 2C7H5N3O6(s) 3N2(g) + 5H2O() + 7C(s) + 7CO(g)arrow_forward
- The normal melting point of benzene, C6H6, is 5.5 C. For the process of melting, what is the sign of each of the following? (a) rH (b) rS (c) rG at 5.5 C (d) rSG at 0.0 C (e) rG at 25.0 Carrow_forwardCalculate the standard Gibbs free-energy change when SO3 forms from SO2 and O2 at 298 K. Why is sulfur trioxide an important substance to study? (Hint: What happens when it combines with water?)arrow_forwardArrange the following sets of systems in order of increasing entropy. Assume one mole of each substance and the same temperature for each member of a set.. (a) H2(g), HBrO4(g), HBr(g). (b)H2O(l), H2O(g), H2O(s). (c) He(g), Cl2(g), P4(g)arrow_forward
- What is the sign of the standard Gibbs free-energy change at low temperatures and at high temperatures for the synthesis of ammonia? 3H2(g) + N2(g) 2NH3(g)arrow_forwardA green plant synthesizes glucose by photosynthesis, as shown in the reaction: 6CO2(g) + 6H2O(l) C6H12O6(s) + 6O2(g) Animals use glucose as a source of energy: C6H12O6(s) + 6O2(g) 6CO2(g) + 6HO2(l) If we were to assume that both of these processes occur to the same extent in a cyclic process, what thermodynamic property must have a nonzero value?arrow_forwardSolid NH4NO3 is placed in a beaker containing water at 25 C. When the solid has completely dissolved, the temperature of the solution is 23.5 C. (a) Was the process exothermic or endothermic? (b) Was the process spontaneous? (c) Did the entropy of the system increase? (d) Did the entropy of the universe increase?arrow_forward
- For ammonia (NH3), the enthalpy of fusion is 5.65 kJ/mol and the entropy of fusion is 28.9 J/K mol. a. Will NH3(s) spontaneously melt at 200. K? b. What is the approximate melting point of ammonia?arrow_forwardIdentify the following processes as either spontaneous or not spontaneous. (a) Ice melts when placed in a flask containing water at 5 C. (b) Hydrogen iodide molecules decompose at 400 K to give a mixture of H2, I2 and HI. (c) Ethanol and water are mixed to form a solution. (d) Slightly soluble PbCl2 (Ksp = 1.7 105) dissolves in water to form a saturated solution.arrow_forwardDescribe why it is easier to use Gto determine the spontaneity of a process rather than S uarrow_forward
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