We say that the overall process, the pressure is constant (i.e., the same at the end as in the beginning) even though in steps 1 and 3, the pressure does change. So, overall, the entropy change for the entire process is not equal to the enthalpy change divided by the temperature. Overall, the entropy of the gases changes in all three steps of the process, but the enthalpy of the gases only changes in the middle step. Here again, the enthalpy change is zero, but, in this case, the entropy changes of the gases are negative. Similarly, for the final third step of the process, the pure product gases are compressed isothermally from their partial pressures in the equilibrium mixture to the total pressure P. So in this step of the process, the enthalpy changes of the gases are zero, but not their entropies increase. Since it is at constant temperature, the enthalpy of the gas is constant, but its entropy increases (because of the pressure change). In general, reversible processes are accompanied by heat exchanges that occur at different temperatures. If there is heat absorbed by the reservoir at temperature, the change in entropy of the reservoir is. This step is not at constant pressure P, and the enthalpy change of the gas is not equal to the heat added. 5 Irreversibility, Entropy Changes, and Lost Work'' Consider a system in contact with a heat reservoir during a reversible process. It will even increase more when water is evaporated to steam (gas). For example, the entropy increases when ice (solid) melts to give water (liquid). Therefore, the system entropy will increase when the amount of motion within the system increases. In the first step, you take each reactant individually and expand it isothermally at T from its initial pressure to its partial pressure in the equilibrium box. Entropy (S) by the modern definition is the amount of energy dispersal in a system. The first step of the overall process is very different from this. When a reaction occurs reversibly, $\Delta S_$$ What determines whether a reaction will be spontaneous is the sum of the changes in entropy of the surroundings and the system. A positive value indicates an increase in entropy, while a negative value denotes a decrease in the entropy of a system.
It is a recurrent subject of confusion to conflate changes in the entropy of the surroundings, of the system, and of the sum of both. Standard molar entropy is defined as the entropy or degree of randomness of one mole of a sample under standard state conditions. In many spontaneous processes, entropy of a. Your logic though is partly correct: exothermic means the entropy of the surroundings increases, as it would do with an increase in T - the catch is that we usually assume that the surroundings has constant T, but that's because we say it has infinite heat capacity. Increasing T will increase entropy due to increase in molecular motion. Exo- and endothermic refer to the direction in which heat is exchanged between system and surroundings, not to changes in the entropy of the system, or of the temperature of either system or surroundings.