Partial pressures by mole fraction:\nA mixture contains 6 moles of H2 and 2 moles of N2 at a total pressure of 4 kgf/cm^2. What is the partial pressure of N2?

Introduction / Context:
Dalton’s law of partial pressures states that, for an ideal gas mixture, each component’s partial pressure equals its mole fraction multiplied by the total pressure. This question checks your ability to compute a partial pressure quickly from composition data.

Given Data / Assumptions:

• Total moles: n = 6 (H2) + 2 (N2) = 8.
• Total pressure: P = 4 kgf/cm^2.
• Ideal-gas behavior and uniform temperature.

Concept / Approach:
The mole fraction of nitrogen is y_N2 = n_N2 / n_total = 2 / 8 = 0.25. Therefore, the partial pressure is p_N2 = y_N2 * P.

Step-by-Step Solution:
Compute mole fraction: y_N2 = 2/8 = 0.25.Apply Dalton’s law: p_N2 = y_N2 * P.Calculate: p_N2 = 0.25 * 4 kgf/cm^2 = 1 kgf/cm^2.

Verification / Alternative check:
The hydrogen partial pressure would then be 0.75 * 4 = 3 kgf/cm^2; the two partial pressures sum to the total (3 + 1 = 4), confirming consistency.

Why Other Options Are Wrong:
Values 2, 4, and 8 kgf/cm^2 correspond to mole fractions of 0.5, 1.0, and 2.0 (impossible), respectively. 0.5 kgf/cm^2 implies a mole fraction of 0.125, not supported by the data.

Common Pitfalls:
Using mass fractions instead of mole fractions; ensure you convert to moles if masses are provided.

Final Answer:
1 kgf/cm^2