Unit 5: Phases of Matter Flashcards
What is thermal energy?
The type of energy that gives matter the ability to move
Temperature of a substance tells you how much thermal energy it has - cold less, hot more
When the amount of thermal energy that matter has changes, its state changes as well (e.g. adding energy moves toward gas)
What are exothermic changes?
Phase changes that release energy - freezing, condensation and deposition.
The gas phase has the most energy and solid the least (liquid is between but closer to solid) so as changes occur to move from gas to liquid or solid, energy is released.
What are endothermic changes?
Phase changes that require energy - melting, vaporization and sublimation.
The solid state has the least energy and gas the most (liquid is between but closer to solid) so as changes occur to move from solid to liquid or gas, energy is needed (e.g. heat needs to be added to liquid for it to become a gas).
What are the physical phase changes?
Ex of sublimation is CO2 (dry ice) - goes directly from solid to gas
Ex of deposition is snow - goes directly from gas to solid (without becoming liquid in between)
Note: If a substance gains energy, the molecules are able to pull themselves apart (e.g. gas) and if it loses energy, the molecules aren’t able to stay apart and get stuck together (e.g. solid).
What does the heating curve of a substance illustrate?
The heating curve of a substance illustrates the relationship between the heat added to a system, its temperature, and its phase.
During the sloped parts of the graph, heating a substance changes it temperature. During the flat parts of the graph, heating a substance changes its phase
Note that, at the melting and boiling points, the temperature does not increase until the phase change is complete
Ex: Ice water remains at 0oC until all of the ice has melted
What is an intermolecular force?
What are the different types?
Attraction between molecules which arise from the interaction of positive and negative charges
3 types (strength assuming similar sized molecules):
- London dispersion forces (weak)
- Dipole-diple forces (medium)
- Hydogen bonding (strong but still 10 times weaker than a covalent bond)
Note: Much weaker than chemical bonds but influence the bulk behavior of the substance; strength of intermolecular forces determines temp at which a substances undergoes a phase change
What are London dispersion forces?
Describes the interactions between a molecule with a temporary dipole moment and the induced dipole moment of it neighbors
Occurs between all atoms and molecules, and it is the only intermolecular force at work in nonpolar substances
Tend to be stronger, the larger the atom or molecule (the larger the electron cloud, the easier it is to distort it, resulting in stronger London dispersion forces)
Relatively weak forces
What are dipole-dipole forces?
Describe the interactions between polar molecules where the partially positive end of one molecule attracts the partially negative end of the other
Stronger than dispersion forces - attractions between polar molecules are stronger than those between nonpolar molecules of similar size
More polar molecules experience larger dipole-dipole forces
Ex: SH2
What is hydrogen bonding?
Special type of dipole-dipole force
An attractive intermolecular force that occurs when a hydrogen atom bonded to O, N, or F (must be a direct covalent bond) is electrostatically attracted to an O, N, or F atom in another molecule (e.g. water molecules being attractracted to each other)
Hydrogen bonds are stronger than normal dipole-dipole forces
What is a temporary dipole moment?
When the electrons of an atom or molecule happen to be more on one side at an instant in time, that side will be more negative than normal, and the other side will be more positive. This situation leads to the formation of a temporary dipole, or instantaneous dipole, which—like any dipole—contains partial charges.
Ex: Both of the electrons on He move to the same side of the atom
What is an induced dipole moment?
Reaction to a temporary dipole moment
When the positive end of the temporary dipole exerts an attractive force on nearby electrons, causing an adjacent atom to develop into another temporary dipole, this is called an induced dipole. This effect passes on to more atoms, resulting in a kind of electron “choreography” in which the movements of the electrons in nearby atoms correlate.
What intermolecular force accounts for the secondary structure of biological molecules?
The term secondary structure refers to the interaction of the hydrogen bond donor and acceptor residues of the repeating peptide unit.
What is a boiling point?
Which molecules have higher boiling points?
The amount of energy needed to overcome the intermolecular forces
The temperature at which boiling occurs—where the vapor pressure equals the external pressure of the atmosphere
Boiling points generally increase with the size of the molecule but some relatively small molecules have high boiling points due to hydrogen bonding (Ex: H2O has a strong hydrogen bond so requires a lot more energy than H2S; thus has a higher boiling point)
Study note: understand pattern - be able to determine which from graph has higher boiling point and why
What are the condensed phases?
Liquids and solids
Intermolecular forces keep the molecules close together
What is the viscosity of a liquid?
Its resistance to flow
Viscosity increases as temp decreases
Stronger intermolecular forces create greater viscosity
Gases have almost no viscosity, liquids have intermediate viscosity, and solids have very high viscosity
Ex: shampoo has relatively high viscosity - pours very slowly
What is surface tension?
The energy required to increase the surface area of a liquid by a unit amount
Surface tension increases as intermolecular forces becomes stronger
Ex: This is why a belly flop hurts and why high divers try to keep themselves as small as possible when entering the water
What is a surfactant?
A substance added to a liquid to disrupt intermolecular forces and lower surface tension
Ex: laundry detergent - reduces the surface tension so the water can wet the clothing better, allowing the detergent to surround the dirt particles
What is capillary action?
The ability of a liquid to climb up narrow spaces
Ex: Water creates a miniscus when you put it in a tube
The meniscus (curved surface of a liquid in a container) may be either concave or convex, depending on whether the intermolecular forces among liquid molecules are greater than or less than the forces of attraction between the liquid and the container walls. Concave for water because the water-glass interactions are stronger than the water-water interactions. In contrast, the intermolecular forces in mercury are stronger than mercury-glass interactions, so mercury tends to withdraw into itself and repel the glass, forming a convex surface.
What are cohesive forces of a liquid?
The forces pulling the liquid molecules together
A cohesive force that is stronger than the adhesive force with the container will cause the liquid form a convex surface or meniscus (e.g. mercury in a glass tube)
What are the adhesive forces of a liquid?
The forces pulling the liquid toward the container
An adhesive force with the container that is stronger than cohesive force of the liquid will cause the liquid form a concave surface or meniscus (e.g. water in a glass tube)
What is a molecular solid?
Solid made up of molecules; can be polar or nonpolar
Many discrete molecules pack together and experience intermolecular forces
What is meant by close packing (of metallic solids)?
Atoms are arranged in efficient, space-saving pattern; each atom is surround / touched by 6 other atoms
Similar patterns seen in nature (e.g. wasp nest)
What is a network solid?
A giant molecule
Chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules and the entire crystal or amorphous solid may be considered a macromolecule.
Ex: diamond, graphite
What is a crystalline solid?
Well organized
Particles arranged in a regular, repeating geometric structure
Happens when the temp of a liquid drops slowly, allowing the particles to become well ordered
Most solids are of this type
Ex: quartz
What is an amorphous solid?
Without form
Particles arranged in a random, nonrepeating fashion; lacks a regular form
Tends to happen when the temp on a liquid drops quickly; long molecules may even get tangled
Ex: glass
What are the general properties of a solid?
Fixed shape
Its own volume
No volume change under pressure
Particles are fixed in place and tends to be in a regular (cyrstalline) array
Symbol: (s)
Note: For most substances, the solid is denser than the liquid; water is the exception due to the unique arrangement of molecules
What are the properties of a gas?
Takes the shape of and fills its container (variable shape and volume)
Volume of the container
Large volume changes under pressure
Particles are widely separated and move independently of one another (low density)
Gases expand & compress uniformly
Gases mix uniformly with other gases in the same container
Symbol: (g)
What are the properties of a liquid?
Takes the shape of its container (may or may not fill it)
Has its own volume
Slight volume change under pressure
Particles are randomly arranged and free to move about until they bump into one another
Symbol: (l)
What are the properties of a metallic solid?
Fudamental Particles: Atoms
Attractive Forces: Attractions between nuclei and delocalized valence electrons
Properties:
- Low melting point and soft OR high melting point and hard
- Good heat and electrical conductors
- Malleable (able to be hammered or pressed permanently out of shape without breaking or cracking)
- Ductile (able to be drawn out into a thin wire)
Ex: Hg, Na, alloys such as Nitinol
What are the properties of an ionic solid?
Fudamental Particles: Cation and anions
Attractive Forces: Ionic bonds
Properties:
- High melting point
- Hard, brittle
- Nonconductors when solid; electrical conductors when melted
Ex: NaCl, KNO3
What are the properties of a molecular solid?
Can be polor or nonpolar
Fudamental Particles: Polar molecules
Attractive Forces: Dipole-diple forces
Properties:
- Low to moderate melting point
- Varible hardness, may be brittle
- Nonconductors
Ex: H2O, CH2Cl2
_______________________
Fudamental Particles: Nonpolar molecules
Attractive Forces: London dispersion forces
Properties:
- Low melting point
- Soft
- Poor heat conductors; electrical insulators
Ex: CH4, S8
What are the properties of a network solid?
Fudamental Particles: Atoms
Attractive Forces: Covalent bonds
Properties:
- Very high melting point
- Very hard, somewhat brittle
- Nonconductors or semiconductors
Ex: C (diamond), SiO2 (silica)
What is the relationship between pressure and tempurature of a gas?
Higher temperature makes the molecules move faster and therefore higher pressure; low temp = low pressure
When molecules collide with a surface they exert pressure
Gas molecules are very small and do not exert much force but there are a lot of them and they collide frequently
What is atmospheric pressure?
The standard pressure a lab would experience at sea level
What is a barometer?
A device used to measure atmospheric pressure
What are the standard units of pressure?
All of these are equity units of pressure
- atmosphere - 1 atm (exactly)
- inches of mercury - 29.9in Hg
- cm of mercury - 76cm Hg (exactly)
- mm of mercury - 760mm Hg (exactly)
- torr1 - 760 torr (exactly)
- pounds per square inch - 14.7 psi
- kilopascal2 - 101kPa
What is Standard Temperature and Pressure (STP)?
Defined as a temperature of 0ºC and a pressure of 1 atm
Under these conditions, all ideal gases have the same molar volume, 22.41 L/mol
What is Boyle’s Law?
At constant amount and temperature, the volume and pressure of a gas are inversely proportional
PV = constant
P1V1 = P2V2
What is Charles’s Law?
At constant amount and pressure, the volume and temperature of a gas are directly proportional
All temperatures must be reported in units of Kelvin!
V/T = constant
V1/T1= V2/T2
What is Gay-Lussac’s Law?
At constant amount and volume, the pressure and temperature of a gas are directly proportional
All temperatures must be reported in units of Kelvin!
P/T = constant
P1/T1 = P2/T2
What is Avogadro’s Law?
At constant temperature and pressure, the amount and volume of a gas are directly proportional
V/n = constant
V1/n1 = V2/n2
What is the combined gas law?
The combined gas law expresses the interdependence of pressure, volume, and temperature
(P1*V1)/T1 = (P2*V2)/T2
What is an ideal gas?
An approximation that helps us model and predict the behavior of real gases. The molecules:
- do not attract or repel each other
- are small and far apart
- move randomly in straight lines
- collide elastically
There are no gases that are exactly ideal, but for temperatures near room temperature and pressures near atmospheric pressure, many of the gases we care about are very nearly ideal.
What is the ideal gas law?
Combines the relationships of all the named gas laws into a single equation
PV = nRT
R = 0.0821 L atm / mol K
R is the ideal gas constant
To use the ideal equation you must convert pressures to atm, volumes to L, and temperatures to K
What is a solution?
A solution is a homogeneous mixture containing a solute and a solvent
Solvent: more abundant component of a solution
Solute: less abundant component of a solution
What is an aqueous solution?
A solution where water is the solvent
How do different types of compounds dissolve in water?
LIKE DISSOLVES LIKE - polar solvants dissolve polar solutes, nonpolar dissolve nonpolar
Ionic compounds dissociate into ions when they dissolve in water
Acids ionize in solution and the H+ ion reacts with water to form H3O+
Molecular compounds are solvated but otherwise unaffected in solution
Which solids are soluable?
Soluble Solids
- Most salts of sodium (Na+), postassium (K+) and ammonium (NH4+) ions are soluable
- All nitrates (NO3-) are soluable
- Most sulfates (SO42-) are soluable
- Most chlorides (Cl-), bromides (Br-) and iodides (I-) are soluable except when combined with Ag, Hg2, Pb
Insoluble Solids
- Silver salts (Ag+)
- Oxides (O2-) and hydroxides (OH-)
- Most carbonates (CO32-)
What is solubility?
Quantification of the amount of a solute that can dissolve in a given amount of solvent
- Saturated: solution contains exactly as much solute as it can dissolve
- Unsaturated: solution contains less solute than it can dissolve
- Supersaturated: solution contains more solute than it can dissolve
Solubility of a solid tends to increase as temperature increases
Solubility of a gas tends to:
- decrease as temperature increases
- increase as the pressure above the solution increases
How do you deterine the molarity of a solution?
Moles of solute / Liters of solution
What is molar volume for an ideal gas?
The volume of 1 mol of an ideal gas at STP (0°C and 1 atm)
22.414 L/mol
