Question

A sample of gas has an initial volume of 4.2 L at a pressure of 736 mmHg. If the volume of the gas is increased to 9.0  L , what will the pressure be?

Express your answer using two significant figures.

Answer 1

We will use Boyle's law. P = 1/V which simply means pressure is inversely proportion to volume at a constant temperature. We will assume temperature here does not change. Since we have two pressure/volume points, we use this version of Boyle's law.

P1 V1 = P2 V2

P is pressure and V is volume

In our case:

P1 is 736, V1 is 4.2 while V2 is 9.0 but P2 is unknown. This is what we need to find out.

736 * 4.2 = P2 * 9.0

P2 = 736 * 4.2 / 9.0

P2 = 3091.2 / 9.0

P2 = 343.5

Therefore the new pressure 343 mm/hg

Here we see that the increase in volume causes decrease in pressure in total agreement with Boyle's law.