Answer: If molecular weight is increased the sound speed will decrease
Explanation: The sound speed in an ideal gas is given by the relationship
v =√((γRT)/M)
When,
R - gas constant = 8.314 J/mol⋅K;
T - the total temperature
M - the molar mass of gas in kg/mol
γ = adiabatic constant of specific gas.
this equation can also be explained as
v2 =((γRT)/M)
So, when T is constant , V squared is inversely proportional to M
Let us use example as an illustrate
assuming that
1st (γRT)= 2 and M= 5
V will be
v2=2/5=0.4=0.632
2nd (γRT)= 2 and M= 10 (notice that we have increased M)
thus
v2=2/10=0.2=0.447
inconclusion, if you increase M(molecular weight) the speed of sound will decrease
