# chemistry

Convert the following pressures to pressures in atmospheres. a. 151.98 kPa
b. 45.6 psi

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1. 1 atm = 101.325 kPa.
1 atm = 14.7 psi

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2. How do I actually do this? I am trying to show my daughter how to do it and have no clue.

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3. Those are conversion factors that I posted. Let's work with the first one. A conversion factor converts anything you have into anything you want (if you have the right factor and use it correctly). So the factor is 1 atm/101.325 kPa and of course it can also be 101.325 kPa/1 atm.

So you want 151.8 kPa converted to atm. That's 151.8 kPa x factor = ? atm. So we could do this two ways, only one of which is correct.
151.8 kPa x (1 atm/101.325 kPa) = ?
OR
151.8 kPa x (101.325 kPa/1 atm) = ?

So which do we pick. We always choose the one in which the unit we want to lose is canceled and the unit we want to stay stays. That is, notice the first way the kPa in the numerator cancels with kPa in the denominator. What unit is left? atm. And that's what we want. We want the answer in atm. If you guessed wrong and used the second way of doing it, notice that nothing cancels. In fact, the unit you get is (kPa)^2/atm which isn't the unit we wanted and you KNOW that can't be right. With practice you want need to do it trial and error but mentally you will place the unit you want to cancel in the bottom of the factor and the unit you want to keep goes on top of the fraction. Hope this helps.

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