# A #7 L# container holds #7 # mol and #18 # mol of gasses A and B, respectively. Every three of molecules of gas B bind to one molecule of gas A and the reaction changes the temperature from #320^oK# to #240 ^oK#. By how much does the pressure change?

##### 1 Answer

The pressure decreases by

#### Explanation:

The key to this problem is to find the number of moles of gas before and after the reaction.

We can then use the ideal gas equation to find the pressure in each case and hence the pressure change.

Before the gases react we have a total number of moles of 7 + 18 = 25

We can write the equation as:

This tells us that 1 mole of

Multiplying through by 6 tells us that 18 moles of

Since we have 7 moles of

So the total moles after reaction = 6 + 1 = 7.

Total final moles = 7

The ideal gas equation gives us :

**Initial:**

(note I have converted

**Final:**

So the pressure has been reduced by