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## Homework Statement

Consider a first order decomposition reaction

2P(g) -----> 4Q(g) + R(g) + S(l)

taking place at a temperature T. After 30 minutes from the start of the decomposition in a closed vessel, the total pressure developed is found to be 317 mmHg and after a long time, the total pressure observed was 617 mmHg. Calculate the toal pressure in the vessel after 75 minutes. (Given : V.P. of S(l) at temperature T=32.5 mmHg)

**Attempt**

Let the initial pressure of P be Pi.

At t=30 minutes, let 2x be the decrease in pressure of P.

There will be a pressure of 4x,x, ? due to Q,R,S respectively.

I have a problem in finding out the pressure of S. How is the partial pressure of S in the vessel related to the state of S? i.e. How do I know whether S will remain a liquid or change into gas? Someone suggested me that if the pressure due to S is say 'y', it will remain a liquid if y > 32.5mmHg.

I don't understand the concept behind it. Can somebody explain?