Final answer:
The most substantial change in average kinetic energy in Kinetic Molecular Theory is due to changes in temperature. As temperature increases, the velocity and hence the kinetic energy of the molecules increase. Absolute zero is when particles are at rest with minimal internal energy.
Step-by-step explanation:
A change to temperature leads to the most substantial increase or decrease in average kinetic energy in Kinetic Molecular Theory. Kinetic energy (KE) is the energy an object possesses due to its motion, and is given by the equation KE = 1/2 mv² where m is the mass and v is the velocity of the molecules.
An increase in temperature causes the particles to move faster, hence kinetic energy increases since it is proportional to the square of the velocity.
Regarding absolute zero, it is the hypothetical temperature at which substances possess minimal internal energy and their particles are at rest, registering no kinetic energy.
If we consider the temperature-volume relationship, we understand that increasing the temperature of a gas will increase its volume if the pressure and amount of gas remain constant. This is because higher temperatures mean higher kinetic energy for the gas molecules, resulting in more forceful collisions with the walls of the container, hence expanding the volume.
Pressure, volume, and the number of particles also play a role in determining the kinetic energy of a gas, but according to Essential Knowledge 7.A.2, it is the temperature that characterizes the average KE of its molecules predominantly.