Salt water steam pressure vs fresh water steam pressure

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Discussion Overview

The discussion revolves around an experiment comparing the steam pressure generated by fresh water versus a salt water solution in a steam-powered boat project. Participants explore the implications of boiling points, vapor pressure, and energy release in relation to the propulsion effectiveness of the two types of water.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant notes that fresh water started producing steam sooner than salt water, but the salt water provided more consistent propulsion.
  • Another participant suggests that the higher boiling point of salt water might lead to higher temperature steam, potentially increasing pressure and kinetic energy.
  • A different participant argues that while steam from salt water may be hotter, the pressure in the tube remains the same for both fresh and salt water since boiling occurs when vapor pressure equals surrounding pressure.
  • One participant challenges the idea that energy output would be identical, suggesting that higher temperature should correlate with higher energy release.
  • Another participant states that hotter steam contains more energy per mass unit, but does not clarify how this affects propulsion.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between temperature, pressure, and energy output in the context of the experiment. There is no consensus on the validity of the conclusions drawn from the results.

Contextual Notes

Participants acknowledge that the experiment's results may involve complexities related to vapor pressure and energy dynamics, but do not resolve these issues or clarify assumptions about the experimental setup.

Who May Find This Useful

Readers interested in experimental physics, thermodynamics, or educational science projects may find the discussion relevant.

Makai
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Homework Statement



My son picked a science experiment for his 5th grade project. It was supposed to be on evaporation. Basically a steam powered boat with candles heating up a cigar tube with a hole for the steam to escape and push the boat. However he got ambitious and changed the experiment with his teacher to see what would work better fresh water vs. a salt water solution. My son theorized that fresh water would push the boat better than salt water after researching about boiling points and elevated boiling points due to the addition of salt water. The conditions were the same as far as time frame, amount of water, and temp of water added to the tube. However his results show that on average the salt water powered boat traveled farther than the fresh water in the same given time. His observations were that the fresh water started pushing steam out sooner than the salt water, however the salt water powered steam was more consistent than the fresh water. Can you point me in a direction that supports these results. Do they sound valid or do we have a case of experimental error. I helped him and made sure that we kept all processes the same so we weren't influencing a result. Is the added solution with a higher boiling point releasing steam at a higher pressure due to more molecular bonds being broken?

Homework Equations





The Attempt at a Solution


He is looking into vapor pressure and is trying to come to a conclusion. Vapor pressure is lowered with salt added to the water so it takes more heat to release vapor so would this create more pressure thus pushing the boat faster.
Thanks
 
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For the salty water escaping vapor has a higher temperature - I would try to think how it can change the propulsion effectiveness. But I am just thinking aloud, I don't have any solid idea about what is happening.
 
It's been a while for me but I am thinking that because we have a higher boiling point the steam would be at a higher temperature thus increasing the pressure in the tube. Therefore we should have an increase of kinetic energy. I'm just trying to make sure we have a valid conclusion.
 
Steam will be hotter, but the pressure in the tube will be identical in both cases - that's because boiling means vapor pressure is equal to the surrounding pressure (which doesn't change).
 
Yes but if you have a higher temp you should be releasing more energy you couldn't have the same result with water vs a solution. Somehow there should be a change more energy in = more energy out.
 
Hotter steam contains more energy at the same pressure.

At least per mass unit.

I think I will move this thread to the engineering section.
 

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