Multiplying both sides of the inequality by reverses the sign of the inequality; rearranging, −T which is equal to We can therefore see that for a spontaneous process, < 0. ΔG. ΔG The relationship between the entropy change of the surroundings and the heat gained or lost by the system provides the key connection between the thermodynamic properties of the system and the change in entropy of the universe. The relationship in the Equation above allows us to predict spontaneity by focusing exclusively on the thermodynamic properties and temperature of the system. We predict that highly exothermic processes (ΔH << 0) that increase the disorder of a system (ΔSsys >> 0) would therefore occur spontaneously. An example of such a process is the decomposition of ammonium nitrate fertilizer. Ammonium nitrate was also used to destroy the Murrah Federal Building in Oklahoma City, Oklahoma, in 1995. For a system at constant temperature and pressure, we can summarize the following results: If < 0, the process occurs spontaneously. ΔG If = 0, the system is at equilibrium. ΔG If > 0, the process is not spontaneous as written but occurs spontaneously in the reverse ΔG direction. To further understand how the various components of dictate whether a process occurs ΔG spontaneously, we now look at a simple and familiar physical change: the conversion of liquid water to water vapor. If this process is carried out at 1 atm and the normal boiling point of 100.00°C (373.15 K), we can calculate from the experimentally measured value of (40.657 kJ/mol). ΔG ΔHvap For vaporizing 1 mol of water, = 40,657 J, so the process is highly endothermic. From the ΔH definition of we know that for 1 mol of water, ΔS,
Multiplying both sides of the inequality by −T reverses the sign of the inequality; rearranging, which is equal to ΔG. We can therefore see that for a spontaneous process, ΔG < 0. The relationship between the entropy change of the surroundings and the heat gained or lost by the system provides the key connection between the thermodynamic properties of the system and the change in entropy of the universe. The relationship in the Equation above allows us to predict spontaneity by focusing exclusively on the thermodynamic properties and temperature of the system. We predict that highly exothermic processes (ΔH << 0) that increase the disorder of a system (ΔSsys >> 0) would therefore occur spontaneously. An example of such a process is the decomposition of ammonium nitrate fertilizer. Ammonium nitrate was also used to destroy the Murrah Federal Building in Oklahoma City, Oklahoma, in 1995. For a system at constant temperature and pressure, we can summarize the following results: If ΔG < 0, the process occurs spontaneously. If ΔG = 0, the system is at equilibrium. If ΔG > 0, the process is not spontaneous as written but occurs spontaneously in the reverse direction. To further understand how the various components of ΔG dictate whether a process occurs spontaneously, we now look at a simple and familiar physical change: the conversion of liquid water to water vapor. If this process is carried out at 1 atm and the normal boiling point of 100.00°C (373.15 K), we can calculate ΔG from the experimentally measured value of ΔHvap (40.657 kJ/mol). For vaporizing 1 mol of water, ΔH = 40,657 J, so the process is highly endothermic. From the definition of ΔS, we know that for 1 mol of water,