Final answer:
According to Boyle's Law, when the volume of gas in a cylinder is halved, the pressure should double if the temperature remains constant. Thus, when the volume decreases from 8.0 liters to 4.0 liters, the pressure increases from 70 kPa to 140 kPa.
Step-by-step explanation:
The question is pertaining to the Boyle's Law, which states that for a given mass of gas at constant temperature, the volume of the gas is inversely proportional to the pressure. This means if the volume of the gas decreases, the pressure should increase proportionally, assuming the temperature remains constant.
In this case, if the volume of a cylinder is reduced from 8.0 liters to 4.0 liters, which is by half, then according to Boyle's Law, the pressure should double. Since the original pressure is 70 kilopascals, doubling this pressure would result in a new pressure of 140 kilopascals.