The molar mass of the gas : 18 x 10⁻³ kg/mol
<h3>Further explanation</h3>
Given
An unknown gas has one third the root mean square speed of H2 at 300 K
Required
the molar mass of the gas
Solution
Average velocities of gases can be expressed as root-mean-square (V rms)

T = temperature, Mm = molar mass of the gas particles , kg/mol
R = gas constant 8,314 J / mol K
v rms An unknown gas = 1/3 v rms H₂
v rms H₂ :

V rms of unknown gas =


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The amount of heat lost by the copper is 2402.4 J.
To Calculate the amount of heat lost, we use the formula below.
<h3>Formula:</h3>
- Q = cm(t₂-t₁)................. Equation 1
<h3>Where:</h3>
- Q = Amount of heat lost
- c = specific heat capacity of copper
- m = mass of copper
- t₂ = Final temperature
- t₁ = Initial temperature
From the question,
<h3>Given:</h3>
- m = 78 g
- c = 0.385 J/g°C
- t₂ = 120°C
- t₁ = 40°C
Substitute these values into equation 1.
- Q = 78(0.385)(120-40)
- Q = 2402.4 J
Hence, The heat lost by the copper is 2402.4 J
Learn more about heat here: brainly.com/question/13439286