Tutorial – Charles’ Law        (Std 4c)

Read through this tutorial very carefully.  It has almost everything that needs to be done in the most difficult of Charles’ Law problems, and goes through the logic of why each step is required.  I hope

this helps!!!!

With Boyle’s Law pressure and volume were inversely proportional.  That means that as one

increases the other decreases.

PV = k    k is a constant

With Charles’ Law temperature and volume are directly proportional.  That means that as

temperature increase, volume must increase also.

V

----   =   b         b  is a constant

T

Using Charles’ Law:

V1        V2                     V1 – starting volume

---   =   ---                    V2 – ending volume

T1        T2                     T1 – starting temperature in Kelvins only

T2 – ending temperature  in Kelvins only

As with Boyle’s law, the unit of measure for Volume must be the same for both V1 and V2.   Another important thing to remember is that pressure and amount of gas cannot change for this law to work.

Example:

We start with temperature at 25 °C and an end with a temperature of 58 °C.  The

volume starts at 75 ml.  What is the final volume?

Solution:

T1 =  25 °C        T2 =  58 °C       V1 = 75 ml      and    V2 =  unknown

We cannot use Charles’ Law until the temperatures are in Kelvins.  Remember that:

°C + 273 = K   which also means that   K = °C - 273

25 °C  +   273 °C  =  298 K = T1

58 °C  +   273 °C  =  331 K = T2

Now we can use these temperatures in Charles’ Law as follows:

75 ml             T2

--------   =   ---------

298 K         331 K

The unit of measure  K  crosses out on both sides of the = sign.  The unit of measure

left is ml.    To finish off the math, multiply 75 ml x 331 and then divide your answer

by 298:                                       Answer        83.3 ml  =  T2