To calculate the absolute pressure of an ideal gas from its partial pressures, you can use Dalton's law of partial pressures. According to Dalton's law, the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.
Mathematically, Dalton's law can be expressed as:
P_total = P_1 + P_2 + P_3 + ... + P_n
where: P_total is the total pressure of the gas mixture, P_1, P_2, P_3, ..., P_n are the partial pressures of the individual gases in the mixture.
So, if you have the partial pressures of all the gases in the mixture, you simply add them together to obtain the absolute pressure of the gas mixture.