Which gas has the highest partial pressure in atmosphere?

Options

A. `CO_2`
B. `H_2`
C. `O_2`
D. `N_2`

Answer

To determine which gas has the highest partial pressure in the atmosphere, we can follow these steps:

### Step 1: Understand Partial Pressure
Partial pressure refers to the pressure that a gas would exert if it occupied the entire volume by itself. It is directly proportional to the mole fraction of the gas in the mixture.

**Hint:** Remember that partial pressure is calculated using the formula:
\[ P_A = P_t \times X_A \]
where \( P_A \) is the partial pressure of gas A, \( P_t \) is the total pressure, and \( X_A \) is the mole fraction of gas A.

### Step 2: Identify the Composition of Atmospheric Gases
The composition of the atmosphere is approximately:
- Nitrogen (N2): 78%
- Oxygen (O2): 21%
- Carbon Dioxide (CO2) and other gases: 1%

**Hint:** Knowing the percentage composition of gases in the atmosphere is crucial for determining which gas has the highest partial pressure.

### Step 3: Calculate Mole Fractions
From the percentage composition, we can deduce the mole fractions:
- Mole fraction of N2: \( X_{N2} = 0.78 \)
- Mole fraction of O2: \( X_{O2} = 0.21 \)
- Mole fraction of CO2 and other gases is negligible compared to N2 and O2.

**Hint:** Mole fraction is simply the percentage divided by 100.

### Step 4: Compare Partial Pressures
Since the total atmospheric pressure is approximately 1 atm, we can calculate the partial pressures:
- Partial pressure of N2:
\[ P_{N2} = P_t \times X_{N2} = 1 \, \text{atm} \times 0.78 = 0.78 \, \text{atm} \]
- Partial pressure of O2:
\[ P_{O2} = P_t \times X_{O2} = 1 \, \text{atm} \times 0.21 = 0.21 \, \text{atm} \]

**Hint:** The gas with the highest mole fraction will have the highest partial pressure.

### Step 5: Conclusion
From the calculations, it is evident that nitrogen (N2) has the highest partial pressure in the atmosphere, which is approximately 0.78 atm.

**Final Answer:** The gas with the highest partial pressure in the atmosphere is **Nitrogen (N2)**.