Tutorial – Boyle’s Law Problems (Std 4c)
Read through this tutorial very carefully. It has almost everything that needs to be done in the most difficult of problems and goes through the logic of why each step needs to be donel. I hope this helps!!!!
Using Boyle’s Law: P1V1 = P2V2
Stated another way: PV = k (k is a constant)
P1 is the first pressure that goes with V1 which is the first volume. When the external pressure or volume of a container changes, the new pressure and volume inside the container will be P2 (the new pressure) and V2 (the new volume), provided we don’t change temperature or moles (amount of gas).
If P1 is given in atm and P2 is given in mmHg, you must convert mmHg to atm,
OR convert mmHg to atm so that both pressures have the same unit of measure.
Also, if V1 is given in liters and V2 is given in ml then you must convert liter to ml
OR convert ml to liter so the both volumes have the same unit of measure.
So, Boyle’s Law tells us how changing pressure will affect volume, or how changing the volume will affect pressure.
If you have P1 = 235 kPa and P2 = 9,500. Torr and V1 = 925 ml, what will V2 be?
You must first change 235 kPa to Torr ( P1 ) so that P1 and P2 are in the same
units of measure and we have to change kPa to Pa before we can change to atm.
. 1000 Pa = 1 kPa and 101,325 Pa = 1 atm and 1 atm = 760 Torr
Use this string of equalities to convert any unit of pressure to any other in one conversion because any one of these equalities is equal to any other equality in the string:
1 atm = 101 kPa = 14.7 psi = 760 Torr = 760 mmHg
235 kPa 760 Torr
------------ x -------------- = 1,768 Torr = P1
1 101 kPa
Now we have everything we need to use Boyle’s Law
P1 x V1 = P2 x V2
1,768 Torr x 925 ml = 9,500. Torr x V2
Divide both sides by 1 Torr to get rid of that unit of measure and also divide both
sides by 9,500. Torr to get that number to the left side of the equation. Now the equation
looks like this:
1,768 x 925 ml
----------------- = V2 Answer: V2 = 172 ml (after rounding)