Kids Awkward Question corner - Solid, Liquid, Gas

Evaporation doesn't need to occur at boiling.

DrP

In evaporation (pond in this example) the particles leave the water from its surface only = Slow.

In boiling (kettle) the bubbles of gas form throughout the liquid. They rise to the surface and escape to the surroundings, forming a gas = Rapid.

Neither of those answers are actually proper answers.

When the evaporation happens, is the water ice, water or steam?

If it leaves slowly, is it still gass, if not how does the water float in the air suddenly?

In a liquid the particles are moving around at the surface a few can"jump out" this is evaporation. When the liquid iss heated the particles move around faster so more can "jump out" at 100°C in water loads are doing this-boiling.

First person to mention water vapour then has to explain if that is ice, water or gas or why have you invented a new catagory of being.*

*She was a know it all 6 year old

Now you've got that far add sublimation to your explanation. Solid ice to gas. 🙂

Just stick her in front of YT and let that answer those questions!

When the evaporation happens, is the water ice, water or steam?

Water is always water regardless of state.

Water vapour does not need to be at 100°C. It's just most of the water will still be liquid.

anagallis_arvensis - Better explanation and is what I said but I made the mistake of mentioning water vapour.

So these jumping particles become water gas? So does that mean water goes from liquid to gas before boiling point? Why do people keep saying it is boiling point then?

Q5 is plain wrong. Boiled water is boiled water. Distilled water is condensed from the atmosphere.

If you have a dehumidifier you can demostrate, or just take something out of the freezer and watch it get wet.

I thought that water that evaporated is not in gaseous state - its liquid molecules suspended in the air.  To be gaseous it needs to be over 100C ?????

First person to mention water vapour then has to explain if that is ice, water or gas or why have you invented a new catagory of being

Water vapour is water as is ice. Water vapour is also a gas.

Solid, liquid and gas are states of matter

Ice is solid water, water vapour is gaseous water and in its liquid form water is just referred to as water which is the confusing bit. Steam is hot water vapour.

First person to mention water vapour then has to explain if that is ice, water or gas or why have you invented a new catagory of being

I guess that is the point it all does it.

Because when the water evaporates it cools the pond. I'd be more worried about them freezing.

Evaporation of water happens at a range of temperatures. It also depends on pressure. Water at the top of mountain boils at a lower temperature than see level.

I have no idea how to explain this to a child or if I even understand it well enough to explain simply to anyone.

Evaporation cools things because the faster particles that are leaving the water take their energy with them so the average kinetic energy of the liquid left goes down. Temperature is just a measure of the kinetic energy of the particles.

Clouds are accumulations of liquid water. They're not gaseous.

Evaporation of water happens at a range of temperatures. It also depends on pressure. Water at the top of mountain boils at a lower temperature than see level.

Yeah that's got me stumped 😀

I guess there is less pressure pushing the particles back into the liquid so they need less energy to escape the surface

I’ll try and explain this for a kid, using the fact that I’m watching frank turner at Reading fest on iPlayer to create an analogy.

Your pond is full of liquid water. Liquid water is in fact made of individual molecules of water, and they’re all somewhat inclined to stick together, much like the crowd of people watching frank turner. Most of the frank turner crowd seem pretty chilled out. They’re not hot and bothered. That’s how temperature works - it’s a measure of the average (or overall) energy level of all the individual molecules. But there are a few individuals watching frank turner that are devoted fans and they’re jumping up and down. They are metaphorically ready to evaporate off into the air! The crowd as a whole still seems pretty cool.

but now frank uses his charm to whip up the crowd to all jump along. It’s like he’s lit a fire under the whole arena. When the song kicks in the whole crowd are jumping. Every single molecule is bouncing with energy, it’s like a boiling liquid.

Best without sound but this will push your ability to explain further:

Clouds are accumulations of liquid water. They’re not gaseous.

that’s right, clouds are drops of liquid or solid (ice) water in suspension of air, which brings us to one of my favourite words: aerosol.

Think like an aerosol paint spray can. Drops of paint in air. You get rain once enough tiny drops (another fave word coming up) aglomerate into bigger drops that are heavy enough to fall out of the sky.

It's either Brownian Motion or as DeLaSoul reckoned - 3.

Either answer is acceptable upto Masters Degree level.

WCA, did you do high school physics or chemistry? Sufficient answers were in those to answer these questions.

I was hoping DrP would thrown in a bit more about probability. Then intermolecular bonds maybe a bit of van Der Waal’s force, and then we’d be off to the races!

That gaseous water exists at <100C must be fairly obvious given humidity or condensation on cold windows.

Most exciting water fact is that solid water is not the densest form. It’s densest at about 4Celsius

Blow their mind with the "triple point" the temperature and pressure at which a substance can exist as a solid, a gas and a liquid in thermodynamic equilibrium.

The water is basically dissolving into the air. So if they are happy with salt into water not being melting that should be ok.

A substance,  in this case water,  doesn't stay entirely in one state wherever it is on the phase diagram (pressure and temperature). The boiling point and the melting point are where the two phases either side of the boundary are in equilibrium,  ie as much ice melts as water freezes. Move either side of that phase boundary either by changing temp or pressure and you no longer have equilibrium so soon have mainly a single phase, ice, liquid or vapour,  but molecules are still coming together or moving apart and bits of the substance change state. That state change is evaporation or condensation etc.

I for one would like to hear an explanation of either sublimation or the triple point in terms of a frank turner gig. Beyond my ability that.

The actual correct answer was "Oooh, shall we have an ice cream?"

You must be a grandparent 😂

Does it show?

Elaboration in case I’m wrong and cause offence: grandparents can escape difficult questions with ice creams. Parents reserve ice creams for the hardest situations or the easiest ways out only when the expected sugar rush can be tolerated. I’m sure you managed either situation expertly wca 🙂

Ok good. If/when I’m a grandparent I’ll just have myself a massive tub of ice cream at my place and a comfy chair. My ***+ kids will have to deal with the rest.

Perfectly deduced. She is indeed my granddaughter which is partly why I was impressed with her telling me about the different states of matter - solid, liquid & gas - so clearly aged 6. Apparently she had been talking to the interesting lady in the tent next to theirs on holiday last week.

I’ll try and explain this for a kid, using the fact that I’m watching frank turner at Reading fest on iPlayer to create an analogy.

Your pond is full of liquid water. Liquid water is in fact made of individual molecules of water, and they’re all somewhat inclined to stick together, much like the crowd of people watching frank turner. Most of the frank turner crowd seem pretty chilled out. They’re not hot and bothered. That’s how temperature works – it’s a measure of the average (or overall) energy level of all the individual molecules. But there are a few individuals watching frank turner that are devoted fans and they’re jumping up and down. They are metaphorically ready to evaporate off into the air! The crowd as a whole still seems pretty cool.

but now frank uses his charm to whip up the crowd to all jump along. It’s like he’s lit a fire under the whole arena. When the song kicks in the whole crowd are jumping. Every single molecule is bouncing with energy, it’s like a boiling liquid.

I still believe

Here's slightly enhanced version the answer I gave my similarly inquisitive 5 year old:

When you add heat to liquid water it speeds up the molecules. Some of that means the temperature of the water goes up (faster molecules = higher temp) and some of them are fast enough to escape as water vapour (evaporate). The more heat you put in the hotter the water will get and the more molecules will escape (hence ponds evaporate in hot weather). Once you get to boiling point any extra heat you put in won't increase the water temperature, it'll just ping more molecules out - the bubbles you see in the liquid have water vapour inside, not air. One of the reasons steam burns are worse than water burns is because steam can be >100 degrees but water can't.

Hope that's useful. It's more or less what I used to teach an S1 class. Not sure if my lad really understands that stuff but he seems to enjoy listening to me talk about science and I'm really chuffed he's asking such questions.

Kids Awkward Question corner – Solid, Liquid, Gas

Poo, pee, fart. Next question?

Water evaporates long before reaching 100c...if it didn't puddles would never disappear after rain as it wouldn't dry up.

The temperature measured by a thermometer represents the average energy of the water molecules. The molecules bounce around randomly, exchanging energy as they do. Some will have higher energy, some will have lower energy. Even though the average energy is below the threshold to evaporate, some individual molecules will exceed that threshold and they will evaporate. When they evaporate, they carry energy with them so the temperature of the liquid drops slightly every time a molecule evaporates. When you boil a kettle, you are pumping energy into the liquid and that energy is then removed by the molecules that evaporate. This means that the remaining liquid stays at a constant temperature (i.e. average energy level)

I thought that water that evaporated is not in gaseous state – its liquid molecules suspended in the air.

No, that’s an aerosol.

Seems to me the problem in learning about this is the plethora of names we give water. Water, ice, steam, water vapour - four names for three phases. Confusion is understandable.

<p style="text-align: left;">The temperature of the water is a measure of the average energy of the molecules. Some of them have more energy, they are the ones that jump out of the liquid and become free in the air.</p>
If the air cools down then the water molecules bump into each other and they no longer have enough energy to escape the water bonds and they clump together into little drops of actual water. This is clouds. Cooler still and they clump together into even bigger drops which can no longer float about and they the fall from the sky as rain.

If the ground cools down outside then the water molecules collect on the grass as they lose energy, this is dew. The reason the air molecules don't form droplets is that the attraction between them isn't as strong so even the energy in  cool air is enough to stop them clumping together.

The thing about 100C is that's the point at which the average energy of the water molecules is enough to break the bonds.

Temperature is a measure of average kinetic energy. Think if a bell curve some molecules are on the extreme right they have enough energy to escape the surface of the puddle and they will. The shape stays the same so there's always enough energy that some molecules will escape. (Draw a line on the RHS of the curve all molecules above this line can escape. Warming pushes the curve to the right so more molecules are above the line evaporation happens quicker.

The escaping molecules when applied to sweat are taking energy away that's why sweating cools you down.

Should have noticed there was a second page.

I always start energy distribution curves in rates at Higher with "why does a puddle dry up?"

Hydrogen bonding innit. Water should actually be a gas at room temperature but the weak hydrohen bonding affect due to the molecules becoming marginally positively and negatively charged due to the oxygen atoms distorting the orbits of the electrons on the hydrogen.

This is why water is most dense at 4 degrees and expands when it freezes, everything else contracts.

And ice cream.

Kids Awkward Question corner – Solid, Liquid, Gas

Given the thread title and the usual interest of kids I was convinced this was going to be a thread about poo.

First person to mention water vapour then has to explain if that is ice, water or gas or why have you invented a new catagory of being.*

*She was a know it all 6 year old

You're donald ducked when she hears about plasma. I'd start reading things if I were you.

Also,

Water is weird and doesn't behave.

Ok, my go at this:

Water = H2O

Air = N2 and O2 plus other bits

Water is therefore lighter than air and would, without a force operating on it be a gas.  As others have said the hydrogen forms weak bonds that generally hold everything together.  However not all bonds are equal and a small increase in energy going in to the liquid (sunlight ambient, temperature, ground being warmer below the surface) can give so me molecules enough energy to break that bond and evaporate.  In the open air this molecule is lighter than the air around it and it rises.  As it goes up the temperature drops and if the molecule touches other molecules and they start to form a vapour.  That is a loose collection of molecules that we see as clouds or mist.

This is the sort of “lies to children” concept that Terry Pritchett used that means that we simplify complex things in to stories that aren’t quite right, but you get the idea.  The more complex explainations (which this may be depending on your audience) mean you loose people and they don’t get the concept, let alone the mechanisms.

It's odd that the assembled minds of the forum can't define the difference between solids, liquid and gas but your bumhole can with almost perfect accuracy.

Seems to me the problem in learning about this is the plethora of names we give water. Water, ice, steam, water vapour – four names for three phases. Confusion is understandable.

Folk talk about steam cos you can see it but it's not a gas. It's a different phase called an aerosol. There's loads of examples of substances that don't quite fit into solid/liquid/gas and they're usually colloids of some sort - that is little bits of one phase suspended in a continuous load of another phase. Aerosols are little bits of liquid suspended in a gas.

Colloids can be a bit counterintuitive and the physics of how they work can be tricky so we tend to leave them out of the model we start with for simplicity's sake. I don't think of this as 'lying to kids' btw, more 'how science works'. We ake some observations and come up with a model to explain/predict them. When we find stuff that doesn't fit the model we change/adapt the model to account for the new stuff.

It’s odd that the assembled minds of the forum can’t define the difference between solids, liquid and gas but your bumhole can with almost perfect accuracy.

You say that but, mine's made mistakes occasionally.

"Sorry love, back in a minute, I just need to go and check that last fart. I think it may have come with prizes."

You've all got it wrong, it's not evaporating, the fish are drinking it!

steam can be >100 degrees but water can’t

Liquid water can be >100 degrees. [ see superheating ]

This is the thing with teaching kids science, everything has to be simplified and exceptions to the rules ignored for brevity and easy recollection. The gaps get filled later. Teaching kids about the triple point of water after years of having 0 and 100 drummed into them as being when state transitions occur, must be a painful task. I wouldn’t want to be a teacher.

colloids

I’ve never heard that word before! Every day’s a school day.

Anecdotally, I read that the purpose of putting a pinch of salt into a pan of water, when cooking pasta, for example, is not for flavour.

It's because the disolved salt in the water raises the boiling temperature of the solution above 100c.

And that helps with cooking it better or something.

Thank you for listening to my TED talk.

Salt reduces the boiling point...it also reduces the freezing point, which is why it gets used on roads when it is looking like 0c temps.

It increases the boiling point as it is entropically unfavourable.  You have to add loads for that value to be significant. You'd be better off increasing the pressure using a sealed container.

Whilst technically true, I can't imagine that a pinch of salt in a panful of water makes a significant difference to its boiling point. You'd be better off putting the pan lid on.

I Am Not An Italian.

I Am Not An Italian.

I bet you put Pineapple on your pizza too! 😉

The real reason to put salt in pasta water is to make the pasta taste better.

‘A pinch’ is vague. If you are cooking 500g of pasta in 5L of water you should add at least 25g of salt. More if you prefer.

I thought impurities typically lower the melting point and increase the boiling point of substances.

I’d imagine, but have not done the calculations or experiments, that 500g of pasta would have a bigger effect than 25g of salt on boiling point.

The melting/boiling changes assume you’ve not changed the ambient pressure or temperature between unadulterated/adulterated tests.

Maybe the pond has a leak....

What's the atmospheric pressure in the vicinity of this pond?

The thing about 100C is that’s the point at which the average energy of the water molecules is enough to break the bonds.

It is the temperature at which the pressure inside a bubble of gaseous water is equal to atmospheric pressure, so that bubbles can grow in shallow water and rise, aka boiling. So water boils at a lower temp at altitude and you can't make a decent cuppa. The pressure the bubbles have to overcome also has a component from the water pressure, so it takes higher temps to boil water at depth eg around hydrothermal vents.

There is also a weak component of pressure holding the water together/ tending to collapse small bubbles from surface tension (which is due to the hydrogen bonds). But that is not enough to keep liquid water drops intact in space, where water exists as ice. Unless it has a planet and atmosphere to provide the necessary pressure.

Ice in space is quite happy as ice because it's at absolute zero. It takes heat to change that hence the tail of a commet as it approaches the sun and warms up relaesign dust and gas which are carried behind it by the solar wind..

Ice in space is quite happy as ice because it’s at absolute zero.

It's actually 2.7 Kelvin in deep space. If you're in the solar system, it will depend how close to the sun and whether you are in shade or not. When the surface of the moon is exposed to the sun, it's above 100 Celsius, but when it's in shadow, it's about as cold as liquid nitrogen.

This was a concept that caused no end of difficulties as a primary school pupil learning about the water cycle.  The idea of water vapour was beyond me.  I got steam, but gaseous water in the air around us - no!

Later I found out what a difficult concept it was to teach.

Ice in space is quite happy as ice because it’s at absolute zero. It takes heat to change that hence the tail of a commet as it approaches the sun and warms up relaesign dust and gas which are carried behind it by the solar wind..

I knew that was not an ideal example to give, anyhow...

Water is also unhappy in space because liquid water cannot exist at low pressures (below the triple point pressure which is around 1/100 of an atmosphere), whatever the temperature. See the phase diagram below, off Wikipedia. If you could somehow transport a bucketload of water into space it would boil (though that word is possibly a bit peaceful for what would happen). The resulting bits would be ice and gas and would have some temperature. The lack of pressure would be the main driver of this, not coooling from the cold of space.

Water phase diagram the image wouldn't link

ETA of course if your bucket is planet-sized, then it can generate enough pressure via gravity for liquid water to exist, and it may also get warm enough somehow.

This was a concept that caused no end of difficulties as a primary school pupil learning about the water cycle.  The idea of water vapour was beyond me.  I got steam, but gaseous water in the air around us – no!

Later I found out what a difficult concept it was to teach.

I think it’s harder because we have special names for solid and gaseous water; harder still because we call the stuff that visibly comes out a kettle the wrong name.  However I think that it makes sense if you ignore water for a moment and think of other liquids.  We seem to get the idea that you can smell many liquids (without actually putting the liquid up your nose).  It doesn’t take too much thought to imagine that this must be caused by some molecules leaving the bulk liquid and becoming vapour? Which can then reach our nose.  Similarly we can all think of liquids that turn solid or vice versa.   Glacial acetic acid would be an easy visualisation.  Solid at fridge temp - liquid at room temp but clearly not boiling, yet you can smell it easily, but heat it up and it boils.  It’s only because we don’t see, smell or otherwise observe water vapour that we forget it is there.  Condensation makes it easy to show it is there though.

Water is also unhappy in space

water is a molecule (or if you mean liquid water a lot of molecules in close proximity) it has no emotions and thus the concept of describing it as happy/unhappy is actually weird.  Sometimes it’s helpful to anthropomorphise atoms/molecules etc but it often leads to limits in our real understanding.  The thought experiment of taking a bucket of water to space depends if you allow it to cool first or it boils before it’s cooled.

water is a molecule (or if you mean liquid water a lot of molecules in close proximity) it has no emotions and thus the concept of describing it as happy/unhappy is actually weird

@poly I am afraid the weirdness is mainly your's. As you later note, people do (often) anthropomorphise things. They are not all weirdos. Furthermore "happy" in such contexts is a common figure of speech, no doubt derived from ideas of what a human would feel but no longer indicating an actual connection with human experience. And further furthermore, thermodynamic happiness is true happiness. As for the thought experiment, it is clear. Water (I can't be arsed to keep calling it "liquid water" where the meaning is obvious) in space. What happens to it. You can't quibble about how it got there because it's a thought experiment. It just got there, all wet and bucket-shaped (the bucket may or may not still be present).