Deriving Standard Molar Entropy of Water

• dbrittain
In summary, the conversation discusses the process of finding and deriving the actual Standard Molar Entropy of various molecules, with a specific focus on liquid water. The standard molar entropy of liquid water can be calculated by subtracting the heat of vaporization from the standard molar entropy of gaseous water and dividing by the standard absolute temperature. To obtain the standard molar entropy of liquid water, one must also measure or know the equilibrium constant for its formation reaction.
dbrittain
Hello everyone, I am a second year physics student attending university, and I have a question about how the actual Standard Molar Entropy of various molecules are found and derived. I have been looking through various Thermodynamics and Chemistry books as well journals online and have all referenced water, for example, to have a standard entropy of around 70 (some are more specific, stating 63.45 J/mol-K etc, but others including some chemistry books state the standard molar entropy to be 69.9 J/mol-K.).

I am specifically interested in how the standard molar entropy of water in liquid form was found.

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If you know the standard molar entropy of gaseous water (a hypothetical state), the standard molar entropy of liquid water is that value minus the heat of vaporization divided by the standard absolute temperature. To get the standard molar entropy of liquid water, you need to measure (or otherwise know) the equilibrium constant for formation reaction.

1. What is standard molar entropy of water?

The standard molar entropy of water is the measure of the amount of disorder or randomness in one mole of water molecules at standard temperature and pressure (STP). It is represented by the symbol S° and has a value of 69.91 J/mol·K.

2. How is the standard molar entropy of water derived?

The standard molar entropy of water can be derived using statistical thermodynamics principles. It involves calculating the number of possible microstates of water molecules at STP and using Boltzmann's formula to determine the entropy value.

3. Why is the standard molar entropy of water important?

The standard molar entropy of water is important because it is a fundamental thermodynamic property that helps in understanding the behavior of water in various chemical reactions and processes. It also serves as a reference point for calculating the entropy of other substances.

4. How does temperature affect the standard molar entropy of water?

The standard molar entropy of water increases with an increase in temperature, as the molecules gain more kinetic energy and become more disordered. This results in an increase in the number of possible microstates and thus, an increase in entropy.

5. Can the standard molar entropy of water be negative?

No, the standard molar entropy of water cannot be negative. This is because entropy is a measure of disorder, and a negative value would imply a negative amount of disorder, which is not possible. It can, however, have a value of zero at absolute zero temperature, where all molecular motion ceases.

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