What are the signs of dH, dS, and dG for the following and please explain why? Also what does it mean by sublimation, and molten?
1. CO2(s) --> CO2(g)
(Dry ice subliming)
dH = ?
dS = ?
dG = ?
2. The electrolysis of molten NaCl(l).
dH = ?
dS = ?
dG = ?
1. For the sublimation of CO2(s) to CO2(g), the signs of dH, dS, and dG are as follows:
dH = + (positive)
dS = + (positive)
dG = ? (undetermined without additional information)
In sublimation, a substance directly transitions from a solid to a gas phase without passing through the liquid phase. Dry ice is the solid form of carbon dioxide (CO2). When it sublimes, it converts from solid CO2 to gaseous CO2.
The positive sign of dH indicates that the process is endothermic, meaning it requires heat energy to break the intermolecular forces holding CO2 molecules together in the solid phase.
The positive sign of dS represents an increase in the entropy or disorder of the system. When CO2 molecules transition from an ordered crystal lattice in the solid phase to a more disordered gas phase, the entropy increases.
The value of dG cannot be determined without the temperature and pressure conditions specified. The relationship between dG, dH, and dS is given by the equation: dG = dH - TdS, where T is the temperature in Kelvin. It is required to determine the spontaneity of the process.
2. The electrolysis of molten NaCl(l) refers to the process of passing an electric current through molten liquid sodium chloride (NaCl).
dH = + (positive)
dS = + (positive)
dG = ? (undetermined without additional information)
The positive sign of dH indicates that the process is endothermic since energy is required to melt the NaCl(l) and break the strong ionic bonds holding the solid together.
The positive sign of dS suggests that the system experiences an increase in entropy. Electrolysis causes the dissociation of NaCl(l) into Na+ and Cl- ions, increasing the disorder in the system.
Similar to the previous case, the value of dG cannot be determined without considering the temperature and pressure. The spontaneity of the process depends on the relationship between dG, dH, and dS, given by the equation: dG = dH - TdS.
To determine the signs of dH (change in enthalpy), dS (change in entropy), and dG (change in Gibbs free energy) for the given reactions, we need to consider the properties of the reactants and products. At the same time, we will explain the concept of sublimation and molten.
1. CO2(s) --> CO2(g) (Dry ice subliming):
Sublimation is the process in which a substance transitions directly from the solid state to the gaseous state, without passing through the liquid state. Dry ice, which is solid carbon dioxide (CO2), undergoes sublimation when it is heated. It goes from a solid to a gas without melting into a liquid.
dH: The reaction involves converting CO2 from the solid state to the gaseous state. Since energy is required to break the intermolecular forces holding the CO2 molecules together in the solid, the process is endothermic. Therefore, dH is positive (+).
dS: Sublimation typically leads to an increase in entropy because the gaseous state has greater molecular disorder compared to the solid state. Therefore, dS is also positive (+).
dG: The equation to calculate dG is dG = dH - TdS, where T represents the temperature in Kelvin. Since dH is positive (+) and dS is positive (+), the value of dG will depend on the temperature. If the temperature is relatively low, dG will be positive (+), indicating the reaction is non-spontaneous. However, if the temperature is high enough, the positive value of dS will dominate, and dG will become negative (-), indicating the reaction is spontaneous. The exact value of dG cannot be determined without knowing the specific temperature.
2. The electrolysis of molten NaCl(l):
Molten refers to a substance being in its liquid state due to high temperature.
dH: In this reaction, molten NaCl (liquid) is being electrolyzed. Electrolysis requires an input of energy to break the chemical bonds in NaCl and promote the reaction. Since energy is needed, the process is endothermic and dH is positive (+).
dS: The electrolysis of molten NaCl(l) involves a transformation from a more ordered state (liquid) to a less ordered state (formation of ions in the solution). The increase in ions and their movement increases the disorder, resulting in an increase in entropy. Thus, dS is positive (+).
dG: Similar to before, dG = dH - TdS, where T is the temperature in Kelvin. Since dH is positive (+) and dS is positive (+), dG will once again depend on the temperature. If the temperature is relatively low, dG will be positive (+), indicating the reaction is non-spontaneous. However, if the temperature is high enough, the positive value of dS might dominate, resulting in a negative (-) value of dG, indicating the reaction becomes spontaneous. The exact value of dG cannot be determined without knowing the specific temperature.
Remember that the sign of dG indicates whether a reaction is spontaneous or non-spontaneous, while the magnitude of dG determines the extent of spontaneity.