A sample of an ideal gas is cooled from 50.0 degrees celsius to 25.0 degrees celsius in a scaled container of constant volume. Which of the following values for the gas will decrease?

1. The average molecular mass of gas.

2. The average distance between the molecules.

3. The average speed of molecules.

Answer: 3 - The average speed of the molecules would reduce.

It has been mentioned that the container in which the ideal gas is cooled from 50 degree Celsius to 25 degree Celsius has constant volume. Since the volume of the container is constant, the molecular mass would remain the same. Also since the volume is constant even though the gas is cooled down, the average distance between the molecules would remain the same.

Since the temperature is reduced from 50 degree Celsius to 25 degree Celsius, the movement and the kinetic energy associated with the gas molecules would reduce. Hence the average speed of the molecules would reduce.

The ideal gas law is PV=nRT where P is pressure, V is volume, n is number of moles of gas, R is the Ideal Gas constant, and T is temperature. In your question, T is decreased by one half. The volume and number of moles of gas are constant, so we are determining the relationship between pressure and temperature. Both temperature and pressure is directly related, meaning lowering the temperature will lower the pressure. And pressure is defined as the frequency at which gas molecules collide with the container. Based on this relationship if temperature is decreased to half, the pressure will be decreased to half, so the answer is 3.