Αποτελέσματα Αναζήτησης
Changes in entropy (ΔS), together with changes in enthalpy (ΔH), enable us to predict in which direction a chemical or physical change will occur spontaneously. Before discussing how to do so, however, we must understand the difference between a reversible process and an irreversible one.
- 4.7: Entropy
Calculate the change of entropy for some simple processes....
- 10.5: Entropy and the Second Law
The thermodynamic arrow of time (entropy) is the measurement...
- 4.7: Entropy
The change in entropy is positive, because heat transfers energy into the ice to cause the phase change. This is a significant increase in entropy, because it takes place at a relatively low temperature.
Calculate the change of entropy for some simple processes. The second law of thermodynamics is best expressed in terms of a change in the thermodynamic variable known as entropy, which is represented by the symbol S. Entropy, like internal energy, is a state function.
So we can calculate the change in entropy of the hot reservoir for a hypothetical reversible process in which 4000 J of heat transfer occurs from it; then we do the same for a hypothetical reversible process in which 4000 J of heat transfer occurs to the cold reservoir.
What does a change in entropy mean, and why should we be interested in it? One reason is that entropy is directly related to the fact that not all heat transfer can be converted into work. The next example gives some indication of how an increase in entropy results in less heat transfer into work.
The thermodynamic arrow of time (entropy) is the measurement of disorder within a system. Denoted as ΔS, the change of entropy suggests that time itself is asymmetric with respect to order of an isolated system, meaning: a system will become more disordered, as time increases.
The total entropy change is the sum of the change in the reservoir, the system or device, and the surroundings. The entropy change of the reservoir is . The entropy change of the device is zero, because we are considering a complete cycle (return to initial state) and entropy is a function of state.
