Question

A sample of nitrogen gas has the temperature drop from 250.°c to 150.°c at constant pressure. what is the final volume if the initial volume is 310. ml?

Answer 1

Charles law gives the relationship between temperature of gas and volume of gas.
It states that for a fixed amount of gas, temperature is directly proportional to volume of gas.
V / T = k
where   V- volume , T - temperature and k - constant 
$\frac{V1}{T1} = \frac{V2}{T2}$
parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation.
T1 = 250 °C + 273 = 523 K
T2 = 150 °C + 273 = 423 K
Substituting the values in the equation,

$\frac{310 mL}{523 K} = \frac{V}{423K}$
V = 251 mL
the new volume is 251 mL