# Tag Info

Accepted

### How are water vapors not visible?

Water vapour is a clear and colourless gas, so it can't be seen by the naked eye. What you see in the photo in your second link is (partially) condensed water vapour, i.e. fog (or mist). Fog contains ...
• 34.4k

### Why does carbon dioxide not sink in air if other dense gases do?

Gases are all miscible. If initially separate and adjacent, they do not mix instantly, but once mixed (a process that occurs by molecular diffusion and is accelerated by macroscopic stirring or ...
• 3,375
Accepted

### Why do gases have weight?

Imagine a gas molecule in a closed box bouncing vertically between the top and bottom of the box. Let's suppose the mass of the gas molecule is $m$ and its speed at the top of the box is $v_t$. When ...
• 331k
Accepted

### Why don't molecules of a gas settle?

You are used to all collisions being somewhat lossy – that is, when you think of most collisions, a little bit of the kinetic energy is lost at each collision so the particles will slow down. If they ...
• 116k
Accepted

### Is there any way for a gas to pass through a solid metal?

Yes, some gases can diffuse into and through metal. It is the bane of the high-vacuum engineer's life. Hydrogen is the worst because it tends to dissociate into atoms at the surface and the nucleus, a ...
• 6,991
Accepted

• 16.7k

### Would a gas "weigh" less than a liquid if they have the same mass?

First of all, it is impossible to have $1L$ of liquid water in vapor form in a $1L$ container. It is difficult for liquid form and the gaseous form to occupy the same volume. The gas molecules would ...
• 6,933
Accepted

### Why (does/we assume) gas exert same pressure everywhere in a closed container?

An imbalance of pressure would itself cause an internal flow in the gas. So if the gas has reached equilibrium the pressure must be the same everywhere. The above is for a gas in ordinary ...
• 47.1k

### Would a gas "weigh" less than a liquid if they have the same mass?

The force the box exerts on the scale will be given by the difference between the force that the gas does downwards on the bottom of the box and the force that it applies upwards to the top of the box....
• 4,525

### If liquid and gas are both chaotic states of matter, what's the difference between them on the molecular level?

The described measurement would allow you to construct the Radial Distribution Function, the probability of finding another particle a distance r from a reference particle usually given as g(r), which ...
• 430
Accepted

### Why can our bodies bleed?

The Systolic and Diastolic blood pressure are measured relative to the atmospheric pressure, hence they are "stronger" than atmospheric pressure. The blood pressure measured (Systolic and ...
• 1,754
Accepted

### Why does the ideal gas law exactly match the van't Hoff law for osmotic pressure?

The law $PV = n RT$ gives the pressure $P$ of $n$ moles of ideal gas in volume $V$. Meanwhile, the law $\Pi V = n R T$ describes the osmotic pressure $\Pi$ due to $n$ moles of solute in volume $V$. ...
• 95.4k

### Why doesn't hydrogen gas exist in Earth's atmosphere?

The other answers are correct in terms of the principal reason that lighter molecules are much more likely to escape the atmosphere. However, it seems that the premise of the question (and perhaps ...
• 5,981

### If the probability of a gas molecule to have any velocity is zero then how can the molecule have any velocity at all?

I think there is a more intuitive argument: Say your average molecule speed in a gas cloud is $20\:\mathrm{\tfrac{m}s}$. Okay, so set up your apparatus and track one particle. And your apparatus ...
• 1,085

### How are water vapors not visible?

Trouble is caused by definitions of steam and vapour in physics and in common language. Physical definition of water vapour and steam is gaseous phase of water. In common language it is "the white ...
• 1,166

### Why do gases have weight?

Think of the atmosphere as if it were an ocean. You might not think water has weight if you were diving underwater, but obviously when you fill up your cup with water you feel its weight increase. The ...
• 341

### Why are sound waves longitudinal even though they are mechanical energy?

In order for mechanical waves to propagate there needs to be some form of "restoring force" that tries to bring the system back to equilibrium. For longitudinal waves in gases this restoring force is ...
• 53.4k

### Could evaporation of a liquid into a gas be thought of as dissolving the liquid in a gas?

I don't think that's a useful perspective to adopt. Fundamentally, dissolution (or solvation) involves particle of the solute being pulled away from the bulk and surrounded by particles of the ...
• 51.9k
In fact, particles in a box of gas are slightly denser at the bottom than they are at the top. In general, the probability of finding a particle with a total energy of $E$ is proportional to the ...