Final answer:
The partial pressure of the second gas in a mixture can be calculated using the total pressure and the given partial pressure of one gas, as per Dalton's Law of Partial Pressures.
Step-by-step explanation:
The question asks about which variable can be calculated when only the total pressure of a mixture of two gases (Ptotal) and the partial pressure of one gas (P1) are given. In this scenario, the variable we can calculate is the partial pressure of the second gas (P2).
According to Dalton's Law of Partial Pressures, for a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of individual gases. Mathematically, this is expressed as Ptotal = P1 + P2, where P1 is the partial pressure of gas 1 and P2 is the partial pressure of gas 2.
If we are provided with Ptotal and P1, we can rearrange the equation to solve for P2: P2 = Ptotal - P1. This shows that if we know the total pressure of the gas mixture and the partial pressure of one gas, we can always find the partial pressure of the second gas.