Question

Based on Kinetic Molecular theory, explain/answer the following: a. Why would inhaling helium make your voice become much higher than normal? b. Why would inhaling sulfur hexafluoride make your voice much lower than normal? c. Would your voice be higher or lower than average if you’re in the hospital and placed in an oxygen-rich environment?

Answer 1

One of the major outcomes of the kinetic molecular theory of gases is that the kinetic energy of all the molecules of a gas remains constant as long as its temperature is constant.

$\therefore KE= CT$ .........................................................[ 1 ]

2 C=-R

and we know that relation between velocity/speed and kinetic energy is given by

..........................................................[ 2 ]

2 KE =-mu

comparing 1 and 2, we get

2 2 RT =-mu

23RI

So, coming to the first case ''inhaling helium makes your voice become much higher than normal'' because helium has lower mass when compared to normal air, therefore the velocity of molecules vibrating to produce sound increases and thus the voice becomes higher.

Coming to the second case ''inhaling sulfur hexafluoride makes your voice much lower than normal'' because sulphur hexafluoride has higher mass when compared to normal air, therefore the velocity of molecules vibrating to produce sound decreases and thus the voice becomes lower.

Coming to the third case, your voice would be higher then the average level if you’re in the hospital and placed in an oxygen-rich environment. Again the reason is the same i.e. due to change in mass, as the molar mass of oxygen [ 15.994 g/mol ] is less than molar mass of dry air[ 28.9647 g/mol ]

NOTE= In any of the case the frequency of molecules vibrating wont change, only the velocity changes. Therefore, normal voice is regained after a while.