18.5 A sealed cylinder (with fixed volume) contains one mole of He gas and is sl

Question

18.5 A sealed cylinder (with fixed volume) contains one mole of He gas and is slowly heated until the temperature of the gas has increased by 50 K. Which of the following statements are correct? (Note: more than one statement may be correct) (a) Rotation of the molecules contributes to the thermal energy (b) The average kinetic energy of the individual atoms of He in- (c) The total thermal energy of the gas increases by 620J (to 2 of the gas as it is heated. creases by 4.2 x 10-19 J s.f.) (d) The density of the gas decreases as the gas is heated. (e) The pressure of the gas decreases as the gas is heated.

Explanation / Answer

According to the given provlem,

Ans: C The total thermal energy of the gas increases by 623J.

Reason:

The change in thermal energy is given by Q = m * c * delta_T where Q is heat, m is mass, c is specific heat, and delta_T is the change in temperature.

You are told it is one mole of helium, so you can determine its mass to be approximately 4 g. You then have to look up its specific heat, which is 3.12 J/g*k. Then the change in temperature is given as 50 K.

Q = 4 g * 3.12 J/g*K * 50 K = 623 J which is close enough to that.

And all other options are wrong.

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