U1 - Module 1: Searching for Differences Flashcards
What are most things in our surroundings considered?
complex systems
What is an example of a complex system?
The air we breath
What are most of the systems that we encounter?
Mixtures
Mixtures
Combination of many different substances
Homogenous Mixture
Uniform composition and properties
What is an example of a homogenous mixture?
Drinking water
Heterogenous Mixture
Composed of visibly different substances that can be in the same or different phases (solid, liquid, gas)
What is an example of a heterogenous mixture?
Minerals on earth
The properties of systems can…
remain constant
or
change on a regular basis
What is an assumption used towards the chemical analysis of substances?
Each substance, no matter how simple or complex, has at least 1 differentiating characteristic that makes it unique.
Differentiating Characteristic
Specific chemical/physical properties used to distinguish substances from each other.
What makes a good differentiating characteristic?
Intensive and unique
Intensive Properties
The bulk properties that do not depend on the amount of matter present.
What are examples of intensive properties?
- Melting point
- Density
- Conductivity
Extensive Properties
Depend on the amount of matter that is present.
What are examples of extensive properties?
- Mass
- Volume
- Energy
Boiling Point
The temperature at which a substance transforms from liquid to gas at a given pressure.
What do normal boiling points consist of?
Boiling temperatures at atp at sea level
Kelvin to C conversion
C + 273.15 = K
atm to Pa conversion
Pa divided by 101325 = atm
atm to mmHg conversion
mmHg divided by 760 = atm
What is the main distinguishing characteristic focused on in this chapter?
Transformation of a pure substance from one phase to another at a constant pressure.
Phase Transition/Change
Transformation of a substance from one state to another.
What 2 things are true about phase change?
- Chemical nature is preserved
- Temperature can be accurately measured.
Transition Point
The slope part of the heat curve
- Adding energy causes temperature to increase
Phase Transition on heat curve
Adding/removing energy induces a change of state, but no change in temperature.
What is the differentiating characteristic during a phase transition?
The energy released per unit of mass
The larger the change in density induced by phase transition…
The larger the energy transfer
Vaporization
Liquid to gas
Freezing
Liquid to solid
Deposition
Gas to solid
Condensation
Gas to liquid
Melting
Solid to liquid
Sublimation
Solid to gas
cal to J conversion
1 cal = 4.184 J
What is phase transition dependent on?
External pressure
Phase Diagrams
Shows the 3 main phases and the values where they occur/co-occur.
What does each substance have?
Its own phase diagram
What do the solid lines in a phase diagram show?
Where phase transition occurs and specifies conditions where 2 conditions simultaneously exist
Triple Point
Where the 3 lines of a phase diagram intersect, displaying where all the conditions coexist.
What is true of the triple point?
The specific values of temperature and pressure at the triple point can be used as differentiating characteristics.
When does density change?
As phase changes from solid to liquid
When do liquid and gas become more alike?
As temperature and pressure increases
Critical Period
The point at the end of the line in a phase diagram that states it impossible to observe another phase change since the liquid and gas are so alike.
Supercritical Fluid
The term used for when the gas and liquid phases are indistinguishable from each other.
Vapor Pressure Curve
An indirect measure of how much a liquid evaporates at a given temperature (liquid to gas phase).
What does the vapor pressure curve trace?
the value of vapor pressure
The higher the pressure of the vapor pressure curve…
-Higher the rate of evaporation
- Larger amount of pressure exerted
When does boiling occur?
When the vapor pressure of a liquid becomes equal to the external pressure
- gas can escape
What is the vapor pressure curve useful in?
Separating liquids
What are the 2 methods of separation?
- Filtration
- Distillation
Filtration
Based on differences in particle size
Used to separate solids from liquids.
What is true about filtration?
It is never complete; some solid will still pass through
What is the efficiency of filtration dependent on?
The filters thickness and pore size
Distillation
Based on differences in boiling points
Gas is cooled down to a liquid and heated up to separate gases based on boiling points.
Is distillation ever perfect?
No - have to distill the different separations collected again
What is the normal boiling point of water?
100 C / 1 atm
What is the normal freezing point of water?
0 C / 1 atm
What is the normal temperature and pressure levels of the critical point?
0.0098 C / 4.58 mmHg
Phase Behavior
The separation and identification of the components of many systems can be done using phase change points (conversion of matter) as “differentiating characteristics”.
Physical Change
The observed behavior is characteristic of all substances undergoing phase change.
When is energy released during a phase transition?
gas to liquid or liquid to solid
- energy levels go down
When is energy absorbed during a phase transition?
solid to liquid or liquid to gas
- energy levels go up
What is the usual starting point for an energy graph?
delta e = 0
Phase Stability
A system tends to remain stable at different values of temperature and pressure.
What happens to the boiling point at higher elevations?
It lowers since the pressure levels are lower.
What effect have differentiating substances had on the development of models?
Oversimplified the models (sometimes wrong)
