# Tag Info

7

Chemistry is very complicated and I'm probably missing certain edge cases, but I think the answer is almost certainly 'no'. Salts lower the vapour pressure of water because intermolecular forces attract the salt ions to the water, raising the energy needed for water molecules to escape. In order for water's vapour pressure to rise, the salt would need to (on ...

6

Liquid evaporation occurs at any temperature, just its rate changes with temperature. You must have seen washed clothes getting dry in open air, water evaporating at room temperature. OTOH, I guess you have not observed boiling sea, lakes or rivers to obtain clouds - putting aside geothermal activities. There are few things for you to understand: Molecules ...

4

The equilibrium is independent on the pressure above the liquid because the mechanism of creating it has nothing to do with the other gases above the liquid It may seem intuitive that a higher gas pressure above a liquid would "push" liquid vapour back into the liquid. But not if you understand how gases work or how a liquid/vapour equilibrium is ...

3

If you heat the commercial concentrated ammonia solution ($25$% $\ce{NH3}$) at usual pressure, it will boil at $32$°C and the vapor contains $3$% $\ce{H2O}$ (and of course $97$% $\ce{NH3}$). So the liquid looses much ammonia and nearly no water. Its total volume decreases a bit but the concentration of ammonia decreases more, so that it is necessary to heat ...

3

I assume you consider the saturated vapor pressure at 100% relative humidity. (As at 50% rel.humidity, vapor pressure = 0.5 saturated vapor pressure). Be aware that ability to contain certain amount of vapor, having respective vapor pressure, is property of space, not of a gas. In first approximation, presence of air or other gas has no effect of ...

3

Evaporation depends on molecular velocity not on the energy The simple mistake in your assumption is that evaporation is driven by molecules having enough energy to escape the liquid phase. This is wrong. Evaporation depends on whether the molecule is travelling fast enough to escape the liquid. The molecules in the liquid will have, on average, the same ...

2

[OP] the average kinetic energy of evaporating water molecules You have to specify whether you are talking about the kinetic energy just before the water molecule breaks the hydrogen bonds to its neighbors or just afterwards. A millisecond before or after the event, of course, the average kinetic energy will be determined by the bulk temperature. One way to ...

2

At gas/liquid phase equilibrium, average kinetic energy of evaporating molecules, i.e. those just passed to a gas phase, is equal to average kinetic energy of condensing molecules. The latter is then approximately proportional to $T$. If these average values were not equal, the system would not be in thermal equilibrium. Feedback to comments: @theorist In ...

2

Azeotropic composition is a function of the boiling pressure and therefore of the boiling temperature. This can be seen in looking up the composition of the constant boiling $\ce{HCl}$ azeotrope with changing atmospheric pressure. However, information on this is hard to find and the effect seems to be small in most cases. Wikipedia does discuss this a bit. ...

2

What I understood: Let's say $\ce{H2O}$ has a (saturated) vapour pressure of $x$ atm at a certain temperature. Now Relative humidity (RH) is the ratio of the partial pressure of water vapour to the equilibrium vapour pressure of water at a given temperature. So what this means is that if RH = 100% then the maximum amount of water vapours is present in the ...

1

As very simple model to find what properties are important in evaporation consider a molecule that when close to the surface moves around in a cell of side $a$ and collides with frequency $f$ into its neighbouring molecules. There is an area $a^2$ through which it can escape the surface and in a second it moves on average a distance $v= 2af$ back and forth ...

1

Assuming that the reservoir does not absorb any heat and there is no loss of heat from the setup by:- Radiation of heat from the reservoir, Convection currents in the air/surrounding fluid (if any), The entire water is at the same temperature so that heat absorbed is not used for increase in temperature, Conduction loss from the reservoir to the ground/...

1

Evaporation rates are used to compare solvents for different reasons and under various conditions. One condition would be under vacuum in a rotary evaporator, to remove a low-boiling solvent to assist crystallization of a solute. Another condition would be in a paint, where you desire a higher boiler to allow enough time to spread the paint without brush ...

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