According to kinetic theory, what does the temperature of a gas actually measure at the molecular level?
AThe speed of the fastest molecule
BThe total kinetic energy of all molecules
CThe average translational kinetic energy per molecule
DThe pressure exerted by molecular collisions
Temperature is proportional to the average kinetic energy per molecule: (1/2)mv²_avg = (3/2)kT. It is not the total energy (which depends on how many molecules there are), not the speed of any single molecule, and not pressure directly (though pressure and temperature are related through PV = NkT).
Question 2 True / False
In a gas at a fixed temperature, most molecules are moving at the same speed.
TTrue
FFalse
Answer: False
Kinetic theory gives the *average* kinetic energy, but individual molecules have a wide distribution of speeds — some moving very slowly, others very fast. This distribution (the Maxwell-Boltzmann distribution) is a key result built on kinetic theory. The temperature fixes the average, not each individual molecule's speed.
Question 3 Short Answer
Explain in molecular terms why compressing a gas into a smaller container (at constant temperature) increases its pressure.
Think about your answer, then reveal below.
Model answer: Smaller volume means molecules hit the walls more frequently, because they travel shorter distances between collisions. With more collisions per second per unit area of wall, the average force on the walls — which is pressure — increases.
Pressure arises from the rate of momentum transfer from molecules to the container walls. Reducing volume while keeping temperature constant (so molecular speeds stay the same) increases the collision rate per unit wall area, directly increasing pressure. This is the microscopic origin of Boyle's Law.