Hi, I posted this question earlier.. 100 g of water, H2O, is heated from 25C to 50C. What is the entropy change for
the process?
Cp = 4.2J/K·mol for water?
I was told 100*4.2ln(323 K/ 298k) was the way to calculate it, it does not produce the correct answer.. I also tried to put water into moles.. 5.55 mole * 4.2 *ln(323/298). The correct answer choice is .34V. I just need to know how to get there. Thanks for your help.
Cp for water=4.179J/gK
entropy=100*4.178 * ln(323/298)
= 33.65J/K
To calculate the entropy change for the process, you need to use the equation:
ΔS = nCp ln(T2/T1)
Where:
ΔS = entropy change
n = moles of the substance (water in this case)
Cp = molar heat capacity (given as 4.2 J/K·mol for water)
T1 = initial temperature (given as 25°C or 298K)
T2 = final temperature (given as 50°C or 323K)
You correctly converted the temperatures to Kelvin, so kudos for that. However, it seems like there was an error in the calculation. Let's go through it step by step:
1. Convert the mass of water to moles:
Molar mass of water (H2O) = 18 g/mol
Number of moles = mass (g) / molar mass (g/mol)
Number of moles = 100 g / 18 g/mol ≈ 5.56 mol (rounded to two decimal places)
2. Calculate the entropy change:
ΔS = nCp ln(T2/T1)
ΔS = 5.56 mol × 4.2 J/K·mol × ln(323 K / 298 K)
Now let's calculate this value:
ln(323 K / 298 K) ≈ 0.08316 (rounded to five decimal places)
ΔS = 5.56 mol × 4.2 J/K·mol × 0.08316
≈ 1.752 J/K
The result is approximately 1.752 J/K, not 0.34 V as you mentioned. It seems there might have been an error in the answer choices or misunderstanding of the units. The correct unit for entropy change is joules per Kelvin (J/K), not volts (V). Double-check the answer choices or clarify the units required.
I hope this explanation helps! Let me know if you have any further questions.