Question

Which of the following gas samples have the greatest average molecular speed at 25°C?

A) Kr
B) CH4
C) N2
D) CH2CI2
E) CO2

Answer 1

• Average Molecular Speed be V

We know

$\boxed{\sf V\propto T}$

$\boxed{\sf V\propto \dfrac{1}{m}}$

• m is molar mass
• Temperature is constant for all.
• So lower the molar mass higher the average molecular speed

Lets find one by one

$\\ \tt\hookrightarrow Kr=83.7g/mol$

$\\ \tt\hookrightarrow CH_4=16g/mol$

$\\ \tt\hookrightarrow N_2=28g/mol$

$\\ \tt\hookrightarrow CH_2Cl_2=86g/mol$

$\\ \tt\hookrightarrow CO_2=44g/mol$

• Lowest is METHANE(CH_4)

Option B is correct.

Answer 2

Answer:

B) Methane, CH4

Explanation:

» For a molecule to have a great molecular speed, it mas have less molecular mass.

• From the samples given,

• Kr → 83 g
• CH4 → 12+(4×1) → 16 g
• N2 → (2×14) → 28 g
• CH2Cl2 → 12+2+(35.5×2) → 85 g
• CO2 → 12+(16×2) → 44 g

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