Unit 1: Module 1 - How do we distinguish substances?

Homogeneous mixtures

combo of substances that have identical makeups and properties

• ex: clean air and drinking water

Heterogeneous mixtures

combo of obviously different substances that can be the same state or different

• ex: mineral in the earth vs minerals in the human body

Differentiating characteristic

measurable trait that makes a substance unique

• (so the substance can be identifiable/recognizable to separate and quantify the different substances present in different places and circumstances)

Good differentiating characteristics should have values that

• doesn’t depend on the volume of the substance that we have (intensive property)

• are unique for each substance

Good differentiating characteristics examples

• melting point

• boiling point

• density

• solubility

• viscosity

• conductivity

Solubility

ability to dissolve in a substance

viscosity

resistance to phase change

Intensive property

doesn’t depend on the volume of a substance available

Extensive property

does depend on the volume of a substance available

• ex: mass and volume

Intensive property BUT not a good differentiating characteristic..

temperature and pressure because they are intensive properties of a system not individual parts

Converting Kelvins (K)

celsius (^oC) + 273.15

Phase Change

chemical composition of the substances remains the same and the changed temperature is measured w/ great accuracy + precision

Understanding phase behaviors are

successful ways to identify and separate many substances of interest

Phase Changes that RELEASE energy

• Freezing (L→S)

• Condensation (G→L)

• Deposition (G→S)

Phase Changes that ABSORB energy

• Melting (S→L)

• Boiling (L→G)

• Sublimation (S→G)

Larger change in density the larger

amount of energy transferred

Don’t use phase change as a D.C when

adding/removing energy from a system causes the chemical composition to change by chemical deposition or reaction with other substances

Normal [D.C like density, melting point, etc]

the differentiating property at a pressure of 1 atm (at sea level)

ΔE

change in energy

Energy Absorbed

(+) (0< ΔE)

Energy Released

(-) (0>ΔE)

Range of temp for a substance changes when

the pressure changes

Phase diagrams

graphs that show visually when a substance changes phases and when it is stable (zones + boundaries)

Triple Point

when the three phases (S/L/G) can coexist w/ each other under the same conditions stably

• ex: water’s TP is at 0.01^oC and 4.58 mmHg

Abrupt density change occurs

between solid and liquid phases, and between solid and gas (at ANY temp + pressure)

Density of Gas and Liquid

have drastically different densities at LOW temps + pressure BUT a HIGH temps + pressure they become more alike

Critical Point

when the temp and pressure reach a specific value, the two phases become identical and impossible to see an actual phase change

Supercritical Fluid

when the temp + pressure are higher than the critical point, the gas and liquid phases are impossible to tell apart

Vapor Pressure

when a liquid enclosed in a container evaporates into a certain extent making vapor that exerts pressure on its surroundings

• Differentiating characteristic of a substance

• Higher temp = Higher rate of evaporation = higher __

Boiling

when the vapor pressure of a liquid equals the externa; [pressure acting on the liquid, the gas freely escapes

Liquids’ Vapor Pressure

due to liquids being more volatile, they have higher vapor pressures than less volatile liquids at any temp

Volatile

substance evaporate faster

Liquids’ boiling point

volatile liquids have lower BP cause their vapor pressure becomes equals to the external pressure at lower temps

• lower BP = lower temp to be reached for it to evaporate = higher vapor pressure