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Homework Help: How do you calculate kpa/min?

  1. Jan 8, 2012 #1
    How do you calculate kpa/min??

    1. I am trying to find the rate of CO2 production in yeast fermentation. I used a gas pressure sensor to measure the kpa every minute. I recorded the initial kpa and the kpa after every minute for four minutes. I forgot how to calculate the kpa/min and need clarification

    2. I think the equation is something like this:
    Initial pressure - final pressure/ (seconds?) I doubt this is right

    3. For instance, the initial pressure was 99.05 kpa and after a minute it was 99.03.
    So would the rate be -.02 kPa/min?
    Can someone please help or steer me in the right direction?
    Any help would be appreciated.
    Last edited by a moderator: Jan 9, 2012
  2. jcsd
  3. Jan 8, 2012 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Re: How do you calculate kPa/minute? Pleaaase help!

    You plot a graph of pressure vs time and find the slope
    (you have more than one data point so you may as well use them)

    Quick-and-dirty method, take the difference between final and initial pressure readings, divide by 4mins.

    Yes - do you need to worry about uncertainty? Best to take values farthest apart: it's change in pressure divided by change in time.
    Measure changes in the units you need - so if you want kPa/min, measure pressure in kPa and time in mins ... if you need psi/decade, then...
  4. Jan 9, 2012 #3


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    Staff: Mentor

    Re: How so you calculate kpa/min??

    Yes, that's the average rate of the pressure change for the first minute.
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