properties of pure substances
TRANSCRIPT
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Prepared By......
Ronak VaghasiyaAs Student,B.E. Mechanical 3rd SemGovernment Engg. Collage Bhavnagar.
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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
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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)
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Examples of Homogeneous mixture
Examples:
•Salt dissolved in water,
•Augar dissolved in water,
•Apple juice,
• Tea,
•Copper (II) sulfate solution in water,
•Alloys....
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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
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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.
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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
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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
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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
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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]
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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]
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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]
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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).
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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.
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P-V-T SURFACE[Expanding]
Any point on p-v-T surface represents an equilibrium state of the substance.
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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.
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Thank you