Answer Show Hint: A reaction is any process in which the starting materials usually called as the reactants are converted to the final products usually called the products. There are two types of reactions on the basis of their occurrence namely, (i) spontaneous reactions, and (ii) non spontaneous reactions. Both the reactions are determined by the physical properties of the thermodynamics. Complete answer: Note: Chapter 18. Chemical Thermodynamics Spontaneity: Free Energy and TemperatureJessie A. Key
In the Gibbs free energy change equation, the only part we as scientists can control is the temperature. We have seen how we can calculate the standard change in Gibbs free energy, ΔG°, but not all reactions we are interested in occur at exactly 298 K. The temperature plays an important role in determining the Gibbs free energy and spontaneity of a reaction. If we examine the Gibbs free energy change equation, we can cluster the components to create two general terms, an enthalpy term, ΔH, and an entropy term, –TΔS. Depending on the sign and magnitude of each, the sum of these terms determines the sign of ΔG and therefore the spontaneity (Table 18.2 “Spontaneity and the Signs of Enthalpy and Entropy Terms”). Table 18.2 Spontaneity and the Signs of Enthalpy and Entropy Terms
Since all temperature values are positive in the Kelvin scale, the temperature affects the magnitude of the entropy term. As shown in Table 18.2 “Spontaneity and the Signs of Enthalpy and Entropy Terms,” the temperature can be the deciding factor in spontaneity when the enthalpy and entropy terms have opposite signs. If ΔH is negative, and –TΔS positive, the reaction will be spontaneous at low temperatures (decreasing the magnitude of the entropy term). If ΔH is positive, and –TΔS negative, the reaction will be spontaneous at high temperatures (increasing the magnitude of the entropy term). Sometimes it can be helpful to determine the temperature when ΔG° = 0 and the process is at equilibrium. Knowing this value, we can adjust the temperature to drive the process to spontaneity or alternatively to prevent the process from occurring spontaneously. Remember that, at equilibrium: We can rearrange and solve for the temperature T:
Using the appendix table of standard thermodynamic quantities, determine the temperature at which the following process is at equilibrium: How does the value you calculated compare to the boiling point of chloroform given in the literature? Solution At equilibrium: We must estimate ΔH° and S° from their enthalpies of formation and standard molar entropies, respectively.
Now we can use these values to solve for the temperature:
The literature boiling point of chloroform is 61.2°C. The value we have calculated is very close but slightly lower due to the assumption that ΔH° and S° do not change with temperature when we estimate the ΔH° and S° from their enthalpies of formation and standard molar entropies.
What are the two conditions for spontaneity?Two conditions for a reaction to be spontaneous are: achieve maximum energy and achieve minimum energy. In thermodynamics, a spontaneous is the time evaluation. Processes which involve an entropy of the system are spontaneous.
What factors make a process spontaneous?Spontaneous processes are reactions which proceed without requiring an input of energy because the products are at a lower, more stable energy state than the reactants. Spontaneous processes often require activation energy, but do not require a prolonged input of energy.
What two factors affect the spontaneity of a reaction quizlet?What two factors determine the spontaneity of a reaction? The size and direction of enthalpy (the heat content of a system at constant pressure [H]) changes and entropy changes together determine whether a reaction is spontaneous; that is, whether it favors products and releases free energy.
What are two examples of spontaneous processes?A spontaneous process is one that occurs on its own, without any energy input from the outside. For example, a ball will roll down an incline; water will flow downhill; ice will melt into water; radioisotopes will decay; and iron will rust.
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