Question

15 mark for review a balloon that contains a sample of gas at room temperature is observed to decrease in size after being placed in a freezer. which of the following best helps explain the observed decrease in size? a the gas particles in the balloon have a lower average kinetic energy at the lower temperature, so they collide with the inside of the balloon less frequently and with less kinetic energy. b the gas particles in the balloon have a lower average kinetic energy at the lower temperature, so a smaller proportion of their collisions are effective. c the pressure in the balloon is lower at the lower temperature, and volume is directly proportional to pressure. d the pressure in the balloon is higher at the lower temperature, and volume is indirectly proportional to pressure.

Explanation:

• Option A: According to the kinetic - molecular theory of gases, temperature is a measure of the average kinetic energy of gas particles. When the temperature decreases (balloon in freezer), the average kinetic energy of gas particles decreases. As a result, gas particles collide with the inside of the balloon less frequently and with less force (lower kinetic energy), causing the balloon to decrease in size.
• Option B: The concept of "effective collisions" is more relevant in the context of chemical reactions (related to activation energy) rather than the simple volume - change of a gas in a balloon due to temperature change.
• Option C: According to Boyle's law \(V=\frac{k}{P}\) (at constant temperature) and Charles's law \(V = kT\) (at constant pressure). The statement "volume is directly proportional to pressure" is incorrect. The correct relationship (at constant temperature) is that volume is inversely proportional to pressure (\(V\propto\frac{1}{P}\)).
• Option D: According to the ideal gas law \(PV = nRT\), at a lower temperature (assuming \(n\) and \(V\) are initially considered, but here \(V\) changes), the pressure should decrease (not increase) when temperature decreases (if we consider \(P=\frac{nRT}{V}\), for a fixed \(n\) and initially fixed \(V\), as \(T\) decreases, \(P\) decreases). Also, the incorrect pressure - volume relationship (volume is indirectly proportional to pressure is a misstatement of Boyle's law, but the pressure change assumption is wrong here).

Answer:

A. The gas particles in the balloon have a lower average kinetic energy at the lower temperature, so they collide with the inside of the balloon less frequently and with less kinetic energy.