Chem H: Unit 2: Matter & Energy

gas

no fixed volume/shape, highly compressible, lowest density

liquid

distinct volume but takes the shape of its container, not/slightly compressible, higher desity

solid

definite volume and shape, not compressible, highest density

evaporation

liquid to gas (boiling water)

condensation

gas to liquid (water condensing)

melting

solid to liquid (ice melting)

freezing

liquid to solid (water freezing)

sublimation

solid to gas (dry ice)

deposition

gas to sold (frost freezing)

pure substance

can’t be separated by physical means, ha distinct properties and a composition that doesn’t vary from sample to sample (subcategories: elements of compounds)

element

can’t be broken down into simpler substances, composed of only one kind of atom, monotonic (1 atom) or diatomic (2 atoms) elements

compound

2 or more different elements chemically combined, can be broken down into simpler substances by chemical reactions

allotropes of elements

different forms of the same element

isomers of compounds

same formula but different structure of a compound

heterogenous mixture

visibly distinguishable parts

homogeneous mixtures

uniform appearance, have no visibly distinguishable parts, any parts of them have the same % composition

physical properties

can be observed or measure without changing the substances composition (color, odor, density, melting, boiling point)

chemical properties

describe the way a substance may change or react to form new substances (flammability, fermentation, corrosion)

extensive properties

depend on the amount of sample (mass, volume, length, energy)

intensive

doesn’t depend on the amount of sample (ALL chemical properties, density, boiling point, luster, inert)

physical changes

physical appearance changes, but not composition (all the phase changes, dissolution)

chemical changes

transformed into a chemically different substance through a reaction (combustion, rusting, dissolving ionic compounds)

Common sense methods (3)

Magnet (based on the magnetism of certain materials, ex: iron powder in cereal), Forceps/sift (based on the size of different substances, ex: wooden splints in sand & salt), Solubility (based on how well a substance dissolves in the same solution, ex: water used to dissolve sand & salt)

distillation

process that depends on the differences in the billing points, more volatile (easy to become gas) vaporizes at lower temps, condenser (cooled tube - changes gas back into liquid). Ex: separating water from sand, separating minerals from sea water

filtration

process that separates a solid from a liquid due to their differences in size. Ex: separating an insoluble (will not dissolve) solid from water

evaporation

process that separates a liquid from a solid based on their different boiling point, liquid cannot be recovered. Ex: separate salt from salt water

chromatography

2 phases - mobile (liquid) & stationary (solid/liquid on solid), the components have different affinities (separation based on binding interactions) for the 2 phases, they will pass through the system, at different times, higher affinity to the mobile phase the further it will travel, highest solubility travels the most, strongest attraction travels the least

energy

the capacity to do work or to transfer heat

work

the energy transferred when a force is applied on an object

kinetic energy

energy created in motion

potential energy

energy stored in objects

heat

form of energy

temperature

random motions of the particles in a substance (higher temp, higher average kinetic energy)

exothermic process

releases heat (freezing, condensation, deposition)

endothermic process

absorbs heat (melting, evaporation, sublimation)

heat of fusion

amount if heat required to change solid to a liquid (no temp change)

heat of evaporation

amount of heat required to change liquid to a gas (no temp change)

vapor pressure

created when the pressure of a vapor in the thermodynamic equilibrium with its liquid state in a closed system, it is the force of the escaping gas molecules posing down on the liquid phase

different liquids at a given temperature

higher vapor pressure means more volatile (evaporates readily), weaker IMF, lower boiling point

same liquid at a given external pressure

higher temperature causes higher vapor pressure, weaker IMF

boiling point

the temperature at which its vapor pressure equals the external pressure