According to the Ideal Gas Equation (PV = nRT), if the temperature and amount of gas are kept constant, what will be the effect of an increase in pressure on the volume of a gas?

• A. As the pressure increases, the volume increases
• B. The volume remains constant
• C. As the pressure increases, the volume decreases
• D. The temperature increases

Answer: (C)

The key idea is that, with temperature and the amount of gas fixed, pressure and volume vary inversely. From PV = nRT, if n and T don’t change, the product PV remains constant. Rearranging gives V = nRT / P, so V is inversely proportional to P. Therefore, as pressure increases, volume must decrease to keep the product constant. This is the isothermal behavior described by the ideal gas law. Increasing volume with higher pressure would violate the equation under these conditions, and calling for a temperature rise would contradict the given that temperature stays the same.