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Mandymassey79 Mandymassey79
wrote...
7 years ago
Let's show the formula for molecular speed at work. Provide a line-by-line solution for the molecular speed of each of the following five gases at 300K: CO, SF6, H2S, Cl2, HBr. You must show your work for each gas to get full credit (6 points for each gas). Finally, use these speeds to help place the five gases in order of increasing average molecular speed i.e. lowest to highest speeds (3 points).
2. Now let's calculate the rms speeds of CO and Cl2 gas by providing line-by-line solutions for each molecule. You must show your work for each gas to get full credit (16 points for each gas). Compare your calculated rms speeds of the CO and Cl2 molecules at 300 K by explaining any potential fundamental differences between the molecules (1 point).
3. The most probable speed formula behaves similarly to the molecular speed formula. Calculate the most probable speeds of the CO and Cl2 molecules by providing line-by-line solutions for each molecule. You must show your work for each gas to get full credit (16 points for each gas). Compare the molecular speeds of the CO and Cl2 molecules at 300 K by explaining any potential fundamental differences between the molecules (1 point). Finally, from your calculations what is the trend in similarities between rms speeds for CO and Cl2 and the most probable speeds for CO and Cl2 (1 point)?
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wrote...
Educator
7 years ago
Hi Mandy, I'm not a chem expert, but does this topic help: https://biology-forums.com/index.php?topic=574117.0
wrote...
Valued Member
7 years ago
As average speed of molecules of gases are given v = SQRT(8RT/pi x M), where R is gas constant, T is Temp. in Kelvin, pi = 22/7 or 3.147 and M is molar mass of the gas. Thus average speed is inversely proportional to the square root of molar mass of the gas.
Now molar masses of CO = 28; SF6 = 146; H2S = 34; Cl2 = 71; HBr = 81
In increasing order molar masses are: CO(28) < H2S(34) < Cl2(71) < HBr(81) < SF6(146)
Therefore, Average speed will be in the order : CO > H2S > Cl2 > HBr > SF6

(b) RMS (Root Mean Square) Speed of the gases = SQRT(3RT/M)
RMS of CO = SQRT ( 3 x 8.314 x 300/28 x 10^-3) = 5.169 x 10^2 m/s (Molar mass in Kg)
RMS of Cl2 = SQRT ( 3 x 8.314 x 300/71 x 10^-3) = 3.246 x 10^2 m/s

(c) Most Probable Speed = SQRT (2RT/M)
OR Most Probable Speed = 0.82 x RMS Speed
Therefore, Most Probable Speed of CO = 0.82 x 5.169 x 10^2 = 4.238 x 10^2 m/s
And Most Probable Speed of Cl2 = 0.82 x 3.246 x 10^2 = 2.66 x 10^2 m/s
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