Which equation represents Dalton's Law for a gas mixture's total pressure?

Which equation represents Dalton's Law for a gas mixture's total pressure?

• A. Ptotal = Pa + Pb + Pc
• B. Ptotal = Pa × Pb × Pc
• C. Pa = Ptotal − Pb
• D. Ptotal = Pa + Pb

Answer: (A)

Dalton's Law is about how partial pressures add up to the total pressure in a gas mixture. Each gas in the mixture contributes its own partial pressure, which is the pressure that gas would exert if it alone filled the container at the same temperature and volume. When you have three gases, their partial pressures simply add: Ptotal = Pa + Pb + Pc. This additive behavior is what makes the expression with a sum the correct representation of the total pressure. The other forms don’t fit the situation. Pa = Ptotal − Pb would only be correct if there were exactly two gases (omitting the third component). Ptotal = Pa × Pb × Pc would imply a multiplicative relationship, which isn’t how partial pressures combine. And a two-term sum would likewise only be valid if there were only two gases. In short, with three components, you must sum all three partial pressures to get the total.

Dalton's Law is about how partial pressures add up to the total pressure in a gas mixture. Each gas in the mixture contributes its own partial pressure, which is the pressure that gas would exert if it alone filled the container at the same temperature and volume. When you have three gases, their partial pressures simply add: Ptotal = Pa + Pb + Pc. This additive behavior is what makes the expression with a sum the correct representation of the total pressure.

The other forms don’t fit the situation. Pa = Ptotal − Pb would only be correct if there were exactly two gases (omitting the third component). Ptotal = Pa × Pb × Pc would imply a multiplicative relationship, which isn’t how partial pressures combine. And a two-term sum would likewise only be valid if there were only two gases. In short, with three components, you must sum all three partial pressures to get the total.