Question

The diagram below shows the temperature dropping from 80°C to 20°C. Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?
1. Molecules vibrate more as temperature decreases.
2. Temperature is not related to the average kinetic energy of a system.
3. Kinetic energy decreases as temperature decreases.
4.. There is no change in average kinetic energy between these two systems.

Answer 1

Answer:

The answer to this question is 3.  Kinetic energy decreases as temperature decreases.

Explanation:

The average Kinetic energy is given by

$K = \frac{3}{2}$ × $K_{B}$ × T where

K = The average molecular kinetic energy of the gas (J)

$K_{B}$ = Boltzmann's constant (1.38×$10^{-23}$ J/K)

T = Temperature of the gas in Kelvin (k)

When the temperature of a given mass of gas drops average kinetic energy of the molecules goes down and the average molecular speed decreases.  The lower kinetic energy  which is the energy of motion of the molecules indicates lower speed of the molecules.

Note that, the kinetic energy and average speed are related by the following formula

KE = $\frac{1}{2}$×m×v²

Where KE = Kinetic energy in Joules (J)

v = the velocity in m/s and

m = the mass of the molecule in Kg