Question

At room temperature (25°C), the particles for which substance would have the highest average kinetic energy?

Sodium
Sodium

Mercury
Mercury

Neon
Neon

Magnesium

Answer 1

Sodium would have the highest average kinetic energy

Further explanation

Kinetic Molecular Theory (KMT) states that a gas consists of molecules that move at a constant and random speed. The collisions between molecules are perfectly elastic so that no energy is wasted.

The molecules move in straight lines until they collide

Energy because this motion is expressed as Kinetic energy (KE) which can be formulated as:

`\tt \displaystyle KE=(1)/(2)mv^2`

Average velocities of gases can be expressed as root-mean-square averages. (V rms)

`\large{\boxed{\bold{v_(rms)=\sqrt{(3RT)/(Mm) } }}`

R = gas constant, T = temperature, Mm = molar mass of the gas particles

So

`\tt KE\approx v\approx (1)/(Mm)`

The substance would have the highest average kinetic energy = the lowest molar mass

Molar mass :

• Sodium : 22,989769 u
• Mercury : 200,59 u
• Neon : 200,59 u
• Magnesium : 24,305 u

From the data above, it shows that Sodium has the smallest molar mass so that it has the largest kinetic energy