# IMAT 2019 Q56 [Ideal Gasses]

A fixed mass of an ideal gas is compressed at constant temperature. The pressure is recorded continuously as the volume decreases. The pressure ( y-axis) and volume (x-axis) are plotted on a linearly scaled graph.

Which statement describes the plotted line?

A. a curved line of increasing positive gradient starting at the origin of the graph

B. a curved line with negative gradient of decreasing magnitude

C. a straight line parallel to the pressure axis

D. a straight line parallel to the volume axis

E. a straight line of positive gradient starting at the origin of the graph

This concept is one of memorization. In Ideal gasses, we know the relationship between pressure and volume is inversely proportional. This is what is called Boyle’s Law.

Boyle’s law states that at constant temperature, the pressure exerted by a gas is inversely proportional to the volume occupied by it . We can therefore eliminate any “straight lined” graphs, being C, D or E.

Since the volume is decreasing in increments, the gradient must be negative. Making our answer B.