Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [phase]

An entity of a material system which is uniform in chemical composition and physical state. This tag should be applied to question regarding chemical and physical properties of phases, systems of phases and also phase transition processes.

4
votes
2answers
395 views

To which state of matter does the flame belong to?

I had this question from the day (9 years old, now 16) that I learned about states of matter. I have asked many of my teachers, some of them told me it's a gas some that it's a plasma. Can anyone ...
15
votes
2answers
36k views

Why does water evaporate at room temperature?

When water temperature reaches $100\ ^\circ \mathrm{C}$, the molecules get so excited that the hydrogen atoms lose the bonds to the oxygen atom and therefore the water starts to become gas. I get that,...
7
votes
1answer
13k views

Caffeine boiling and melting points

According to both caffeine's pubchem page and chemspider page its boiling point lies at 173°C and its melting point at ~235°C. How can it melt at that temperature if it already sublimated at 173°C? Or ...
3
votes
1answer
497 views

Phase diagram analysis

The figure is a portion of the titanium copper phase diagram for which only single-phase regions are labeled. Specify all temperature composition points at which eutectics, eutectoids, peritectics and ...
1
vote
2answers
814 views

Can these changes be reversed by changing temperature?

An egg turning hard when boiled. A spoon full of batter cooking on a hot griddle. I said that they both cannot be reversed, because I think if you throw both the egg and batter into the freezer, it ...
1
vote
1answer
62 views

Is there a element that shows this pattern of boiling point?

Is there a compound that turns to gas at a certain temperature but if heated more turns back to liquid and if heated more than turn to gas? Does it exist naturally? Has a such a substance be found? ...
2
votes
2answers
844 views

Why is water evaporation not more commonly used to cool buildings [closed]

Water has a very high heat of vaporization (2260 kJ per kg). Why not just gradually sprinkle water on your roof to keep the building cool in opposed to using air conditioners? It wouldn't take much ...
5
votes
1answer
2k views

Which elements have no liquid form at atmospheric pressure?

Carbon has no liquid form at atmospheric pressure. Is this unique amongst naturally occurring elements? The more interesting and vague question is, is this property somehow important or related to ...
8
votes
3answers
2k views

What non-toxic non-water substances have a freezing point very close to water's?

I was linked to a Kickstarter for a cooling ball to be placed in drinks which claims with constant marketing hyperbole how much it relies on "Phase Change" ! which is a neat concept and seems not ...
2
votes
1answer
97 views

Why do molecules have to first transform to gas before doing a reaction?

I have to calculate the enthalpy of the reaction $$\ce{Cs(l) + 1/2I2(s) -> CsI(s)}$$ and the answer is $$\Delta H_f = \Delta H_{vap}^{\ce{Cs}} + \frac{1}{2}\Delta H_{subl}^{\ce{I2}} + \frac{1}{2}E_{...
14
votes
1answer
2k views

Why is the carbon dioxide we exhale transparent?

Why is carbon dioxide that comes from dry ice opaque and smoky while the carbon dioxide that we exhale transparent?
36
votes
6answers
394k views

Why does ice water get colder when salt is added?

It is well known that when you add salt to ice, the ice not only melts but will actually get colder. From chemistry books, I've learned that salt will lower the freezing point of water. But I’m a ...
10
votes
3answers
148k views

How can melting point equal freezing point?

I don't understand how melting point = freezing point. For example, if liquid water freezes at 0 °C how can ice also melts at 0 °C?
4
votes
1answer
10k views

What is the effect of adding salt to ice?

What will happen to the melting point temperature of ice if some common salt is added to it? How to justfy the answer?
6
votes
1answer
7k views

Why does heat solidify cake batter?

Increased vibration causes the atoms in an object to spread out farther away. Thus, with added heat, and object goes form a solid to a liquid to a gas (and then to plasma, with enough heat). Why is it ...
1
vote
1answer
108 views

What determines a substance's energy of activation with air?

Ice will melt when heat is applied; paper will catch fire. In trying to figure out why — what the difference is between things that melt and things that catch — I found "Burn, Char, Melt" by Roberto ...
5
votes
1answer
2k views

Why does water become less dense when it cools

Most materials become more dense as they cool, but ice floats in water, meaning that it's less dense. Why is this?
4
votes
1answer
3k views

What defines matter's phase at room temperature?

So, a simple question: what makes neon a gas; what makes water liquid; what makes plutonium-238 a solid at room temperature? Of course, the phase is determined by the excitation of the molecules, but ...
5
votes
1answer
224 views

Lennard Jones liquid vapor phase transition

I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen ...
6
votes
1answer
876 views

Does sublimation happen only on the surface or throughout the body?

Like evaporation happens only on the surface of a liquid, and boiling/vapourisation takes place throughout the body, how does sublimation occur? Why?
5
votes
4answers
2k views

Phase diagram for first 10 elements

I've been looking on the net for a reference which shows a phase diagram for elements at least from $\ce{H}$ up to $\ce{Ne}$. Specifically, I'm looking which of these elements can be solid or liquid ...
5
votes
4answers
16k views

What is the difference between melting and dissolving?

What is the difference between melting and dissolving? I am looking some general features. The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (...