a) Mencione dos ejemplos de procesos endotérmicos que sean espontáneos. b) Dé un ejemplo de un p

A) Mencione dos ejemplos de procesos endotérmicos que sean...

Key Concepts

Endothermic Process

An endothermic process is one in which the system absorbs heat from its surroundings, resulting in a positive enthalpy change (?H > 0). Despite the absorption of energy, such processes can still be spontaneous if the increase in entropy (?S) of the system or surroundings is sufficiently high to overcome the energy absorbed, as determined by the Gibbs free energy equation.

Spontaneous Process

A spontaneous process is one that occurs naturally without needing an external input of energy. The spontaneity of a process is governed by the Gibbs free energy change (?G), where a negative value (?G < 0) indicates that the process can proceed on its own as it is thermodynamically favorable. This concept is fundamental in physical chemistry and thermodynamics, providing a criterion for predicting the direction of chemical reactions and physical transformations.

Temperature Dependence of Spontaneity

Temperature dependence of spontaneity arises from the relationship defined by the Gibbs free energy equation, ?G = ?H - T?S, where T is the absolute temperature. A process may be spontaneous at one temperature and non-spontaneous at another depending on the relative contributions of enthalpy (?H) and entropy (?S). This concept explains why some reactions or phase transitions only occur under certain thermal conditions, making temperature a critical factor in determining the overall feasibility of a process.

Transcript

00:01 So in this particular problem, we're looking for two examples of processes that can be both endothermic and spontaneous.

00:10 And remember, for something to be spontaneous, we have to have a gibbs free energy that's negative.

00:16 But in this particular case, we're given the fact that we have an endothermic process, which makes delta h positive.

00:23 So in order for that to work out for something to be both endothermic and spontaneous, that must mean that in this particular, term, we're either going to have to have high values of temperature or a high value in the change of entropy to have this boxed in terms so negative that it makes the delta g negative.

00:48 Two straightforward examples of this to see would have to do with water.

00:55 And if we remember the heating curve of water, we know that the melting point of water is at zero degrees celsius.

01:04 We know that the boiling point is at 100 degrees celsius.

01:08 And to have substances change states of matter, we need to be able to have a temperature surrounding it over the temperature which that phase change will occur.

01:22 So we can think about, for instance, melting.

01:27 And we know melting occurs at zero degrees celsius.

01:30 But if we have the temperature, if we set the temperature greater than that.

01:34 If we have an ice cube sitting in our homes at 20 degrees celsius, we know that spontaneously melts.

01:42 So the heat from the room is going into the ice cube to break the intermolecular forces, heat in endothermic.

01:54 And we know that something like melting an ice cube, as long as the temperature is high enough, is spontaneous.

02:01 So we can say melting an ice cube, but we also need to specify the temperature.

02:08 As long as the temperature is over zero degrees celsius, that's fine.

02:12 So for instance, we can say at 20 degrees celsius, like room temperature...

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