Final answer:
When a gas is heated at constant volume, its pressure and the kinetic energy of the molecules increase due to more frequent and forceful collisions. The attractive forces between molecules are not significantly affected.
Step-by-step explanation:
When a gas is heated at constant volume, there are several effects observed. According to Amonton's law, if the temperature is increased, the average speed and kinetic energy of the gas molecules increase. Since the volume is held constant, the increased kinetic energy causes molecules to collide more frequently and with greater force against the container walls, thus increasing the pressure. Increase in molecular kinetic energy is a direct consequence of the temperature rise, as kinetic energy is proportional to the square of the velocity of molecules (KE = mv²).
Under these conditions, the attractive forces between molecules do not increase significantly with temperature. That's because these forces depend more on the molecular nature and closeness of the gas molecules rather than the temperature. Furthermore, as the temperature of a gas increases, any increase in attractive forces is overshadowed by the increased kinetic energy that tends to separate the molecules.