Final answer:
Exhaling 0.5L of air against 1 atm of pressure results in positive work done, which is calculated using the pressure-volume work formula and equates to 0.5 L·atm or 50.66 Joules.
Step-by-step explanation:
When exhaling 0.5L of air from our lungs against a pressure of 1 atm (101 kPa), we are doing positive work. To calculate the pressure-volume (PV) work done, we can use the formula W = PΔV, where W is work, P is pressure, and ΔV is the change in volume. Given that the external pressure (P) is 1 atm and the change in volume (ΔV) is 0.5L, the work done can be calculated as:
W = PΔV = (1 atm) × (0.5 L) = 0.5 L·atm
Since 1 L·atm is equivalent to 101.32 Joules, the work done in Joules can be calculated as:
W = 0.5 L·atm × 101.32 J/L·atm = 50.66 Joules
This computation shows that work must be done by the body to exhale air, as the lungs have to push against the atmospheric pressure. Moreover, if we convert this to the SI unit of Joules using the conversion 1 L'atm = 101.32 J, we see that the work done by the lungs is indeed positive.