Question

The diagram below shows the temperature dropping from 80°C to 20°C.

Two containers each hold 4 balls. One container has balls with long arrows indicating movement and is labeled 80 degrees Celsius. The other has balls with short arrows and is labeled 20 degrees Celsius. An arrow points from the first to the second container.
Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?
Molecules vibrate more as temperature decreases.
Temperature is not related to the average kinetic energy of a system.
Kinetic energy decreases as temperature decreases.
There is no change in average kinetic energy between these two systems.

Answer 1

Kinetic energy decreases as temperature decreases.

Explanation: Temperature is proportional to the average kinetic energy of the molecules. Lower temperature (20°C vs 80°C) means the molecules on average move more slowly (shorter arrows), so their average kinetic energy is lower.