Change of state

2018年4月12日

Change of state

The state (solid, liquid, gas) of the change of state … material change. Because a change of state happens, the mass does not change, but the volume changes.

※The change of state is caused by a change of the temperature, but is caused by the change of the atmospheric pressure. For example, water usually becomes the gas at 100 degrees Celsius, but it is to gas at 20 degrees Celsius by lowering the atmospheric pressure.

※Because the temperature of the material rises, the motion of molecules of the material becomes active. Because I express the speed of the motion of these molecules, as for the temperature, time when the speed of this exercise became 0 becomes the minimum of the temperature.

I call temperature of this time an absolute zero point (-273.15 degrees Celsius). In addition, the upper limit of the temperature does not exist. (endlessly)

A fusion … solid become the liquid

A vaporization … liquid become the gas

Condensation … gas become the liquid

A solidification … liquid become the solid

Direct, sublimation … gas become the solid. Or direct, a solid become the gas.

Dry ice (solid) becomes carbon dioxide (gas) example 1 of the sublimation.

When naphthalene used example 2 of the sublimation for as insect repellent noticed it, I disappeared. (solid ⇒ gas)

Temperature during a change of state

The figure which expressed time and relations of the temperature when heated ice, and made a change of state following; show.

The following things feeling two points by all means are important from this figure

When a change of state happens, the temperature does not change.
When a change of state happens, it is in a condition that two states were mixed.

Only at the age of the pure material that other materials are not mixed in a graph levelling out it during a change of state in this way.

A change of state and heat

・When water becomes the steam, the water absorbs neighboring heat (evaporation heat). As a result, neighboring temperature falls.

An example: On the day when the summer was thick, temperature of the neighborhood fell by watering the way (sprinkled water)

An example: After doing a long-distance running, and having finished running, health cooled off suddenly. (the sweat which I exercised, and hair had vaporized and took the heat of the body away)

In addition, as for this phenomenon, the reverse thing happens. In other words

・When steam becomes the water, the steam releases heat (heat of condensation) in the neighborhood. As a result, neighboring temperature rises.

Change of the volume by the change of state

When a change of state happens, the volume changes, but the way of the change is divided into 2 patterns of “water” and “the material except it”.

Please refer to the page of the property of the material for the calculation of the density.

[in the case of water]

	Solid (ice)	Liquid Wednesday	Gas (steam)
Mass	$1 g of {}$	$1 g of {}$	$1 g of {}$
The volume	$3 {1.1cm }^{}$	$3 {1.0cm }^{}$	$3 {1,700cm }^{}$
Density	$0.9 g/cm of 3 {}^{}$	$1.0 g/cm of 3 {}^{}$	$0.000588 g/cm of 3 {}^{}$

When you changed in ice, steam on the basis of water because it is hard to image increase and decrease relations only with となるが, a number, you should understand it well in the next figure how the volume changes.

[) that, in the case of a material except the water, (“ろう” is made questions for as an example well]

	Solid	Liquid	Gas
Mass	Normal	Normal	Normal
The volume	Small	Normal	Large
Density	Large	Normal	Small

When I make it plain visually

I look such. The change of the volume when it became the solid from a liquid in comparison with a case of the water is reversed.

There is a lot of learning it,; but at first

In the case of a change of state of the water, I learn how the volume changes
The change of the volume at the age of the ⇒ solid liquid at the age of a material except the water at the age of the water is reversed

I have only to learn these two points.

In addition, because mass does not change,

The density makes move that it is reverse to the change of the volume

You should learn ということも. (because it is that a formula of the density can say, it is not the knowledge that you should learn by all means)

A melting point and the boiling point

Temperature when a melting point … material performs a change of state to a solid from a liquid or a liquid from a solid

Temperature when a boiling point … material performs a change of state to a liquid from gas or gas from a liquid

If atmospheric pressure is constant, a melting point and the boiling point are fixed by a material. For example, as for the melting point of the water, the boiling point of the water becomes 100 degrees Celsius at 0 degrees Celsius.

Material	Melting point (℃)	The boiling point (℃)
Water	0	100
Ethanol	－115	78
Naphthalene	81	218
Oxygen	－218	－183
Salt	801	1413

With this list,

[exercise] Answer in the state of each material at 20 degrees Celsius.

The issue of という is made questions for well,

If if is less than a melting point, exceed a liquid, the boiling point between a solid, a melting point and the boiling point; gas. You should feel it in a という style.

[gas]　　⇔ melting point ⇔【 liquid 】⇔ boiling point ⇔【 gas 】

Water … liquid

Ethanol … liquid

Naphthalene … solid

Oxygen … gas

Salt … solid

The distillation

I heat a mixture using difference in distillation … boiling point and correct it to a liquid again after making gas, and divide it into each ingredient.

※Because, by the distillation, I cannot take out a pure ingredient, but can divide it into an ingredient having high purity to some extent,

When I divide crude oil into each ingredient, it is applied.

As for the problem of the distillation in an entrance examination and the regular examination, a problem of mixture “of” ethanol and the water is almost made questions for.

Ethanol evaporates earlier when I distill this because the boiling point is lower ethanol. But, it is to watch out because I cannot take out pure ethanol!

When take out the liquid which distill a mixture of ethanol and the water, and is provided for wind called test tube ①⇒ test tube ②⇒ test tube ③; the ingredient of the contents

Water of test tube ① … rather much ethanol & a bit
Test tube ② … ethanol and water as for the half-and-half
Ethanol & rather much water of test tube ③ … a bit

It is necessary to learn that ratios of water increase so as to be a liquid provided in a という style later.

I return to a list of units

Chemistry

Posted by Lese