which of the following is not spontaneous process at 25 degrees celsius and 1 atm pressure?
ice melting
iron rusting
salt dissolving
steam condensing
water boiling
To determine which of the following processes is not spontaneous at 25 degrees Celsius and 1 atm pressure, we need to understand the concept of spontaneity and use thermodynamic principles.
Spontaneity refers to whether a given process or reaction occurs naturally without requiring external influence. In thermodynamics, spontaneity is determined by the change in Gibbs free energy (ΔG) of the system. If ΔG is negative, the process is spontaneous, while if ΔG is positive, the process is non-spontaneous.
Now, let's evaluate each of the processes:
1. Ice melting: The phase change from solid ice to liquid water occurs at temperatures above the freezing point. Since melting ice is a spontaneous process, it releases heat and results in a decrease in Gibbs free energy. Therefore, ice melting is a spontaneous process.
2. Iron rusting: The process of iron rusting involves the reaction between iron, oxygen, and water, leading to the formation of iron oxide (rust). This process is also spontaneous, as it occurs naturally over time due to the tendency of iron to oxidize in the presence of oxygen and moisture.
3. Salt dissolving: Dissolving salt, such as sodium chloride (NaCl), in water is a spontaneous process. When salt dissolves, the ions in the solid interact with the water molecules, resulting in a decrease in Gibbs free energy.
4. Steam condensing: The process of steam condensing involves the conversion of water vapor (steam) into liquid water when it loses heat. This phase change from gas to liquid is spontaneous, as it leads to a decrease in Gibbs free energy.
5. Water boiling: Boiling occurs when the temperature of the liquid reaches its boiling point, and the liquid is converted into a gas (vapor). This process is spontaneous, as it results in the conversion of water to steam, increasing the system's entropy and leading to a decrease in Gibbs free energy.
In conclusion, all the listed processes (ice melting, iron rusting, salt dissolving, steam condensing, and water boiling) are spontaneous at 25 degrees Celsius and 1 atm pressure.
I think what you must do here is to calculate dSsurroundings + dSsystem and see if it is + or - dS (or you can go through dG = dH - TdS and see if the rxn is + or - dG.
I assume you can find dH and S in your text. For
H2O: S for ice is about 20 but you need to confirm that. S for liquid water is about 70 so dS for the system is about +50 (70-20= +50)
dSsurounding = -dHrxn/T = -6000J/298 = about -20 J/mol.
dStotal = dSsurr + dSsys = -20J + 50 = +30. Since it is + the system is spontaneous. The others are done the same way.