Question

A sample of helium gas has a pressure of 1.20 atm at 22°c. at what celsius temperature will the helium reach a pressure of 2.00 atm, assuming constant volume?

Answer 1

Gay-Lussac's law gives the relationship between pressure and temperature of a gas.
it states that for a fixed amount of gas of constant volume pressure is directly proportional to temperature. 
P/T = k
where P - pressure, T - temperature and k - constant 
$\frac{P1}{T1} = \frac{P2}{T2}$
where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation.
temperature should be in the kelvin scale,
T1 = 22 °C + 273 = 295 K
substituting the values in the equation 
$\frac{1.20atm}{295 K} = \frac{2.00 atm}{T}$
T = 492 K
new temperature - 492 - 273 = 219 °C