We can use Boyle's law to solve this problem, which states that for a constant temperature, the volume of a gas is inversely proportional to its pressure. The formula for Boyle’s law is:
\[
P_1 V_1 = P_2 V_2
\]
Where:
- \( P_1 = 1.0 \, \text{atm} \) is the initial pressure,
- \( V_1 = 5.0 \, \text{L} \) is the initial volume,
- \( P_2 = 2.0 \, \text{atm} \) is the final pressure,
- \( V_2 \) is the final volume, which we need to find.
Rearranging the formula to solve for \( V_2 \):
\[
V_2 = \frac{P_1 V_1}{P_2}
\]
Substitute the known values:
\[
V_2 = \frac{1.0 \times 5.0}{2.0} = 2.5 \, \text{L}
\]
Thus, the volume of the gas at 2.0 atm pressure is \( 2.5 \, \text{L} \).