The first-order decomposition of phosphene to phosphorus and hydrogen
4PH3(g) → P4(g) + 6H2(g)
has a half-life of 35.0 s at 680°C. Starting with 520 mmHg of pure phosphene in an 8.00-L flask at 680°,
how long will it take for the total pressure in the flask to rise to 1.000 atm?