Question

Dry air near sea level has the following composition by volume: N2, 78.02 %; O2, 20.94 %; Ar, 0.93%; and CO2, 0.05 %. The atmospheric pressure is 1.00 atm. Calculate the partial pressure of each gas in atm. PN2 = ? atm PO2=? atm PAr= ?atm PCO2= ?atm

Answer 1

1. Dry air near sea level has the following composition by volume: N2, 78.02%; O2, 20.94%; Ar, 0.93%; and CO2, 0.05%. The atmospheric pressure is 1.00 atm. Calculate the partial pressure of each gas in atm. PN2 = ? atm PO2=? atm PAr= ?atm PCO2= ?atm

Solution:

We have:

$$P = 1 \text{ atm}; \quad k_{N_2} = 78.02\%; \quad k_{O_2} = 78.02\%; \quad k_{Ar} = 78.02\%; \quad k_{CO_2} = 78.02\%$$

Lets suppose, that we have ideal gases. So, according to Dalton's Law:

$$P = P_{N_2} + P_{O_2} + P_{Ar} + P_{CO_2}$$

Obviously,

$$k_i = \frac{P_i}{P}$$

where $P_i$ is the pressure of certain gas, $k_i$ - coefficient (proportion) of certain gas. Hence,

$$P_i = k_i \cdot P$$

For our gases, we have (Answer):

$$P_{N_2} = 0,7802 \cdot 1 \text{ atm} = 0,7802 \text{ atm}; P_{O_2} = 0,2094 \cdot 1 \text{ atm} = 0,2094 \text{ atm}$$ $$P_{Ar} = 0,0093 \cdot 1 \text{ atm} = 0,0093 \text{ atm}; P_{CO_2} = 0,0005 \cdot 1 \text{ atm} = 0,0005 \text{ atm}$$