A closed vessel contains equal numbers of o2 and h2...

A closed vessel contains equal numbers of O2 and H2 molecules at same T . Which of the following is not true? A. The average speed of the hydrogen molecules is greater B. The hydrogen molecules strike the walls of the vessel more often C. The average kinetic energy of the two gases is the same D. The weight of H2 is the same as the weight of oxygen

Transcript

00:02 Hi there.

00:03 In this question, we have a closed container that contains an equal number of o2 molecules.

00:12 So the number of o2 molecules equals the number of h2 molecules.

00:24 And they are both at the same temperature.

00:27 We want to know which of the following is not true.

00:30 Let's look at what we have here.

00:31 It's a closed vessel and we have equal numbers.

00:35 So the things that are equal here, are going to be the number of moles because the number of molecules is going to be we could convert that to number of moles it's a closed vessel so it has a set volume so the volume is equal we are at the same temperature so since the number of moles the volume and the temperature are all equal the pressure is also equal so the number of moles the volume the temperature and the pressure are all equal.

01:09 So we want to know what is not equal, which is not true here.

01:13 Well, before we go further, let's look at the periodic table and look at the atomic masses of these, or the molecular mass.

01:20 Since it is 02, we need 16 times 2, which gives us 32 .00 amu as the molecular mass of oxygen.

01:36 Similarly, for the hydrogen, it's 1 .01 amu per atom, and there are two of those, so it's going to be 2 .02 amu.

01:47 Okay, i think we have enough information here to start looking at the answer options and try to determine which of these is not true.

01:57 Okay, so the first one talks about the average speed of the two molecules.

02:01 Well, let's use the equation kinetic energy is equal to one -half mass times velocity squared.

02:12 Kinetic energy is dependent upon temperature, and these are both at the same temperature.

02:18 Therefore, since the mass of the hydrogen is less than the mass of the oxygen, the velocity of the hydrogen must be greater than the velocity of the oxygen.

02:32 Just looking at this equation, because mass and volume squared are going to be inverse relationship, is going to be an inverse relationship.

02:40 Therefore, yes, the average speed of the hydrogen molecules is greater...

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