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.

Example:

If you have P1 = 235 kPa  and  P2 = 9,500. Torr and  V1 = 925 ml, what will  V2  be?

Solution:

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)

9,500.