Properties of pure substances

Prepared By......

Ronak VaghasiyaAs Student,B.E. Mechanical 3rd SemGovernment Engg. Collage Bhavnagar.

MATTER

Heterogeneous mixture

Is it uniform throughout?

No

Homogeneous

Yes

Can it be separated by physical means?

Pure Substance Homogeneous Mixture (solution)

Can it be decomposed into other substance by a chemical process?

Element Compound

No yes

No yes

Homogeneous Substances

• Means same throughout

1) element: only 1 type of atom

2) compound: 2 or more CHEMICALLY combined elements (not easily separated from each other)

ex: water, CO2

3) Solution: a special kind of mixture 2 phases/parts (SOLUTE dissolves & SOLVENT does the dissolving)

ex: moist air (H2O in Air); sterling silver (Cu

in Ag…called an alloy)

Examples of Homogeneous mixture

Examples:

•Salt dissolved in water,

•Augar dissolved in water,

•Apple juice,

• Tea,

•Copper (II) sulfate solution in water,

•Alloys....

A pure substance of constant chemical composition throughout its mass.

It is a one-component system. It may exist in one or more phases. Here we take water as the representative of a pure

substance.

INTRODUCTION ABOUT PURE SUBSTANCE

Phase of Pure Substance

The substances exist in different phases, e.g. At room temerature and pressure ,copper is solid and mercury is a liquid.It can exist in different phases under variation of conditionThere is 3 principal phases•solid•Liquid•GasEach with differnt molecular structures.

BASIC[1]

Triple Line/Point

• Area where all three phases can exist;– Line on P-v and T-v diagrams– Point on P-T diagrams

BASIC[2]

Sublimation• Two ways a substance can

go from solid to vapor:– Melts to liquid, then

vaporizes to vapor– Evaporates directly with

out first melting, sublimation

• Happens at pressures below triple point value

P-V DIAGRAM FOR PURE SUBSTANCE[1]

Assume a unit mass of ice(solid water) at -10’c and 1 atm contained in a cylinder and piston machine.(Fig. 1)Let the ice be heated slowly so that its temperature is always uniform.

Heating of H o at a ₂constant pressure of 1 atm.

Fig. 1

Let the state changes of water be plotted on P-V coordinates

1-2 The temperature of ice increases from -10˚C to 0˚C.The volume of ice Would increase,as would be the case for any solid upon heating.At state 2 i.e., 0˚C,the ice would start melting.

2-3 Ice melts into water at a constnt temperature of 0˚C.At state 3,the melting process ends. There is a decrease in volume,which is a peculiarity of water.

P-V DIAGRAM FOR PURE SUBSTANCE[2]

3-4The temperature of water increases,upon heating,from 0˚C to 100˚C.The volume of water increases because of thermal expantion.

4-5 The water start boiling at state 4 and boiling ends at state 5.This phase change from liquid to vapour occurs at a constant temperature of 100˚C(the pressure being constant at 1 atm).There is a large increase in volume.

P-V DIAGRAM FOR PURE SUBSTANCE[3]

5-6 The vapour is heated to,say 250˚C(state 6).The volume of vapour increases from v ₅to v₆.

P-V DIAGRAM FOR PURE SUBSTANCE[4]

P-V DIAGRAM FOR PURE SUBSTANCE[5]

All the state changes of the system can similarly be plotted on the p-v co-ordinates, when it is heated at different constant pressures.All the saturated solid state 2 at various pressures are joined by a line(fig).

P-V-T SURFACE

The relationship between pressure,specific volume,and temperature can be clearly understood with the aid of a

three dimensional P-V-T surface.

1. Expand upon freezing[WATER]2. Contract upon freezing[OTHER THAN WATER]

There are two different surface for different

substance of P-V-T surface.

P-V-T SURFACE[Expanding]

Any point on p-v-T surface represents an equilibrium state of the substance.

P-V-T SURFACE[Contracting]

The triple point line when projected to the p-T plane becomes a point.The critical isotherm has a point of inflection at the critical point.

Thank you