Class 3 Phases and Gases
Boyle's Gas Law
"Boiling Point" = Boyle's Law = Vapor Pressure P is inversely related to V (constant n, T) (if you increase volume of container gas molecules have more room to move around and aren't hitting container walls, therefore pressure decreases) AT CONSTANT TEMPERATURE P : (1/V) or P1V1=P2V2
Charles's Gas Law
"Charles is on TV" T is directly proportional to V (constant n, P) (decrease temperature of a gas, molecules move more slowly, then they take up less space) AT CONSTANT PRESSURE T : V or (V1/T1)=(V2/T2)
Gay-Lussac's/Amonton's Gas Law
"Gay-Lussac is your PT" P is directly proportional to T (constant n, V) (as you increase pressure, the gas is going to heat up because the molecules are closer together and hitting each other more) AT CONSTANT VOLUME P : T or (P1/T1) = (P2/T2)
aVogadro's Gas Law
"if two equal-volume containers hold gas at the same pressure and temperature, then they contain the same number of particles (regardless of the identity of the gas" = the volume of a sample of gas is proportional to the number of gas particles in the container (the greater the number of gas molecules = the greater the volume it will fill) - gas stoichiometry can be done using volumes: V : n (=Avogadro's Law) The volume of an ideal gas is proportional to the number of particles in the container at a given P and T, regardless of the identity of the gas One mole of ANY ideal gas occupies 22.4 L at STP (1 mole = 22.4L) - STP is defined as OC (273K) and 1 atm *see notes for ex; may need to find LR first then get moles
Role of IMF in Physical Properties Pt2: Vapor Pressure
(Pvap) = is the force exerted by the gas particles that vaporize from a solid or liquid sample
Non-Ideality (IMF)
Because the particles of a real gas DO experience IMF, their paths are deviated and thus the frequency of collisions on the container wall result in a lower pressure (molecules aren't hitting container walls - too busy interacting with each other) - curved path of real gas molecules is longer, so it takes more time to hit container wall = lower pressure Pideal > Preal
Non-Ideality (Particle Size)
Because the particles of a real gas DO have physical size, they take up space in the container and thus the free space in the container is smaller Videal > Vreal
Combined Gas Law
Boyle's, Charles's, Amonton's Laws can be combined to change two variables at once: (P1V1/T1) = (P2V2/T2) - gas law problems can be used solving proportions - the number of moles are still constant when using the combined gas law - P and V units can vary but temperature must be in K
Melting and Freezing Point (relationship: pressure, temperature, IMFs)
(mp/fp) is the temperature at which the fusion/crystallization phase transitions occur - S-> L = fusion - L -> S = crystallization The freezing point and melting point are identical and follow the same rules Trends: - external pressure is directly proportional to mp/fp, as external pressure increases so does mp/fp (this doesn't apply to water because increase in pressure causes shift towards liquid phase and not toward solid phase) - IMF is directly proportional to mp/fp; increase IMF strength will have higher mp/fp - meaning the stronger the IMF, the more the substance is going to want to be in solid form (instead of converting to liquid form)
Ideal Gas Law
* V = 1/P (Boyle's) *V=T (Charle's) *T=P (Guy-Lussac/Amonton's) combine to form: PV=nRT (R=0.08 Latm/molK) - many ideal gas law problems can be simplified using 22.4L/mol at or near STP 1) use PV=nRT if asked to solve for a missing variable 2) use (P1V1/T1) = (P2V2/T2) if asked "before and after" scenarios
Phase Diagrams
**notice positive slope for solid liquid boundary line - the solid/liquid boundary represents the trend in fp/mp - liquid/gas boundary represents the trend in bp - triple point = the one T&P when all 3 phases coexist in equilibrium - critical point = the T&P above the which the difference between liquid and gas is no longer distinct - above critical point = supercritical fluid *most phases have a positive-sloping melting/freezing point line, making the solid phase the most dense Water follows the same general trends except at the solid-liquid boundary line: *exception for water: negative slope because we have H-bonding IMFs (2LP on O and 2H's bonded = up to 4 H-bonds) densityice (more H bonds, trapping air) < densitywater - the fp/mp of ice decreases under increasing pressure (if temp is constant, increasing pressure causes ice to melt) P2 >P1 T2<T1
Phase Diagrams pt.2
*water exception negative slope: temperature is constant as pressure increases at solid - liquid boundary; this can favor the liquid phase, not the solid phase (as would be the case for most other substances like CO2) - the solid water (ice) is melting (turning to a liquid) as pressure increases ex: as the blade of an ice skate bearing all of the weight of the skater contacts the ice, the pressure increases, melting the ice under the blade and allowing the skate to glide over the liquid water (dashed vertical line shown on pg. 152 shows this effect). As the skater moves across the ice, each blade continually generates a thin layer of liquid water that refreezes as the blade passes. - the properties of CO2 don't allow for skating because solid CO2 (dry ice) will never turn to liquid when the pressure is increased *water has the peculiar property of being denser at around 4°C than it is colder or warmer than that: this is why ice floats on water, whereas almost no other solid phases of materials would float on their respective liquid phases.
Real Gas Law (Van der Waals Equation)
*would be given to you* How much greater is the ideal world (in terms of pressure and volume) than the real world? - real gas behavior can be accounted for under extreme P and T conditions - the pressure term (P+an^2/V^2) takes into account the attraction between real gas particles (a increases as the IMFs of a gas get stronger) - the volume term (V-nb) accounts for the volume occupied by the real gas particles (b increases as the size of the gas particle increases)
Dalton's Law (pg. 171)
- The partial pressure of a gas is proportional to its mole fraction (X) states that the total pressure of a mixture of gases is equal to the sum of their partial pressures: Ptotal = Pa+Pb+...Pn Pn = partial pressure Pa=XaPtotal where Xa = na/ntotal
supercritical fluid
- beyond the critical point, the substance displays properties of both a liquid (such as high density) and a gas (such as low viscosity). - if a substance is in this state - where the liquid and gas phases are no longer distinct - its called supercritical fluid, and no amount of increased pressure can force the substance back into its liquid phase
In order for a solid to turn into a liquid the temperature and pressure must (in a phase diagram)
- both increase - THINK POSITIVE SLOPE
Vapor pressure (relationship: pressure, temperature, IMFs)
- is a measure of the tendency of a material to change into the gaseous state Trends: - decrease BP, increase Pvapor - external pressure has NO EFFECT on Pvap (it is only the pressure of the gas particles we are concerned about) - external temperature has direct effect on Pvap; (increase temp, enable more particles to enter gas phase which would allow them to exert a greater vapor pressure) - IMF is indirectly proportional to Pvapor; stronger IMFs will be harder to break interactions between particles and will have less molecules in gas phase. So the stronger the IMF the lower the Pvapor
Heating Curve (Temperature Change)
- it requires heat energy (q=mCAT) to raise temperature - slope on graph is where temperature change occurs m = mass (g) c = specific heat (J/gC=J/gK) C = mc = heat capacity (J/C=J/K)
Temperature
- physical changes are closely related to this - is the measure of the amount of internal KE that molecules have - KE is also related to entropy (disorder); the higher the KE of the molecules of a substance, the higher the entropy
The solute can be a
- strong electrolyte = complete dissociation (anything that is strong will dissociate 100% = strong acid, strong base, strong electrolyte) - weak electrolyte (partial dissociation) - non-electrolyte (no dissociation) The van't Hoff factor (i) is the number of particles produced in solution per mole of substance C6H121O6 (i=1) NaCl (i=2) Ca(NO3)2 (i=3) HF (1<i<2) = weak acid HCl (i=2) = strong acid
Phase Transition Diagram/Heating Curve
- the process requires input of heat (S to L to G) - flat lines = when a substance reaches its melting point (mp) and boiling point (bp) - DURING A PHASE TRANSITION, THE TEMPERATURE OF THE SUBSTANCE DOES NOT CHANGE (flat lines: q=nH) - the greater the value for the heat of transition the longer the flat line - a substance's heat of vaporization is always greater than its heat of fusion (BC MORE IMFS MUST BREAK FROM L>G VS. S>L) - the sloped lines show how the temperature changes (within a phase) as heat is added - since T=q/C, the slopes of the non-flat lines are equal to 1/C, the reciprocal of the substance's heat capacity in that phase (heat capacity, C = mxc(specific heat)
Units of Pressure
1 Pa = 1 N/m^2 at sea level, atmospheric pressure = 100kPa = 100,000Pa = 1 atm at 0C, 1 torr = 1mmHg 1 atm = 101,000 Pa = 760 torr = 760 mmHg = 100 kPa
STP
1 mol = 22.4 L (must divide 22.4/4 if sample has 0.25mol) T = 0C or 273K P = 1 atm = 10^5 Pa = 10^2 (100) kPa = 760 mmHg = 760 torr #of gas particles = (#moles) x (6.02x10^23 particles/mol) # particles at STP would be (1 mole) x (6.02x10^23 particles/mol) = 6.02x10^23 particles
The most important criteria for an ideal gas are:
1. The molecules do not liquefy at low temperature. 2. The molecules do not experience intermolecular forces. 3. The molecules have negligible volume. (The molecules having negligible mass is NOT a criterion for a gas to be considered ideal.)
Rules to follow for calorimetry problems:
1. the specific heat of a substance also depends upon phase. For example, the specific heat of ice is different from that of liquid water 2. The SI unit for energy is the joule, not the calorie. Specific heats and heat capacities may be given in terms of joules rather than calories (1 cal = 4.2J) 3. Specific heats may also be given in terms of kelvin rather than degrees Celsius; ie. 4.2J/gxK rather than 4.2J/gxC - however since the size of a Celsius degree is the same as a kelvin (if two temperatures differ by 1C, they also differ by 1K), the numerical value of the specific heat won't be any different if kelvins are used
Kinetic Molecular Theory of Gases WHAT CONDITIONS OF temperature and pressure do ideal gases favor?
2 most important: - an ideal gas has ZERO IMFs - an ideal gas has particles with negligible volume/size compared to their container size (will have smallest MW/period) - an ideal gas has an average KE proportional to its temperature **ideality is favored with high temperature and low pressure since interactions of the particles are minimized** - an ideal gas has elastic collisions between particles and container walls* (*creates pressure) (elastic collisions = the total KE is the same after the collisions as it was before) Q: raising temperature causes gases to behave more ideally Q: decreasing pressure causes gases to behave ideally
Why is temperature constant during any phase change? A. All phases have the same energy, so no temperature change is observed during the phase transitions. B. Energy is used to break or form bonds rather than change temperature during a phase change. C. Energy is used to break or form intermolecular forces rather than change temperature during a phase change. D. Added or removed energy either decreases or increases the entropy of the system, respectively, thereby making temperature changes impossible.
= C. Energy is used to break or form intermolecular forces rather than change temperature during a phase change. Solids, liquids, and gases all have different potential energies (they are listed in order of increasing energy) so choice A can be eliminated. While a phase change does affect the entropy of the system, adding energy makes a more disordered system, thereby increasing entropy (eliminate choice D). A phase change is a physical, not chemical process, so no chemical bonds are broken or formed in the process (eliminate choice B). The energy added to a system causing a phase change is used to break the intermolecular forces holding molecules together rather than make molecules move faster (associated with a temperature change).
Units of Volume
= L, m^3, mL, cm^3 1 cm^3 = 1cc (cubic centimeter) = 1 mL 1 m^3 = 1000L 1L=.001m^3=1,000mL=1000cm^3
Vaporization
= boiling Liquid to a gas Heat is absorbed Internal KE increases Entropy increases
Where would the dissolved gas be highest in a shallow body of water? Top Middle Bottom Constant
= bottom because gas is directly proportional to pressure - assume temperature is constant throughout water
Crystalization
= freezing liquid to a solid Heat is released Internal KE decreases Entropy decreases
Fusion
= melting Solid to a liquid Heat is absorbed Internal KE increases Entropy increases
Heat of transition (equation?)
= the amount of energy required to complete a phase transition (deltaH) - each substance has a specific heat of transition for each phase change, and the magnitude is directly related to the strength and number of the intermolecular forces that substance experiences The amount of heat required to cause a phase change depends on 2 things: 1. the type of substance 2. the amount of substance (mol) *if deltaH and q are positive = heat is absorbed (S>L>G) *if deltaH and q are negative = heat is released (G>L>S) n= number of moles of substance (or mass if deltaH is given in energy/mass)
Solids
= the most ordered and least energetic of the phases - as a solid absorbs heat its temperature increases, meaning the average KE of the molecules increases - this causes the molecules to move around more, loosening the intermolecular interactions and increasing entropy - when enough energy is absorbed for the molecules to move freely around one another, the solid melts and becomes liquid
Calorimetry
= the science of measuring changes to determine heat transfer "When a substance absorbs or releases heat, one of two things can happen: either its temperature changes OR it will undergo a phase change BUT NOT BOTH AT THE SAME TIME" *adding heat can also raise the temperature of a substance, increasing irs average KE (incline on graph) q = McdeltaT q = heat added to (or released by) a sample c = specific heat = intrinsic property of that substance and how resistant it is to changing its temperature m = mas or moles depending on units of c (use whichever will cancel out) C = heat capacity = mc
The van der Waals equation for real gases: contains two constants which have unique values for each gas. When comparing these constants for neon and argon, the constant "b" is larger for argon because: A. argon atoms have greater real volume than neon. B. argon has more protons than neon. C. argon has stronger intermolecular forces than neon. D. argon has a greater density than neon.
A. argon atoms have greater real volume than neon. The constant "b" is a correction for the real, finite volume of gas molecules. The larger the value of "b", the larger the gas in question. As such, choice A is correct. The number of protons does not have a consistent relationship to molecular volume (eliminate choice B). Density (which is mass/volume), has no correlation to the van der Waals equation (eliminate choice D). The correction for intermolecular forces is contained in the constant "a" (eliminate choice B).
liquids
At the molecular level, the molecules in a liquid are still in contact and interact with each other, but they have enough KE to escape fixed positions - liquids have more internal KE and greater entropy than solids - if enough heat is absorbed by the liquid, the KE increases until the molecules have enough speed to escape intermolecular force and vaporize into the gas phase
Electrolytes in Water that are USUALLY insoluble:
Ag+ (silver) Pb2+ (lead) Pb4+ (Hg2)2+ (mercury) Hg2+ (CO3)2- (carbonate) (PO4)3- (phosphate) S2- (sulfurs) *if you have something that is usually insoluble like Ag+ coupled to something that is soluble like NO3- = will be soluble
Each of the following equations shows the dissociation of an acid in water. Which of the reactions occurs to the LEAST extent? TRY TO IDENTIFY ACID AND CONJUGATE BASE FOR STABILITY A. HCl + H2O → H3O+ + Cl− B HPO42− + H2O → H3O+ + PO43− C H2SO4 + H2O → H3O+ + HSO4− D H3PO4 + H2O → H3O+ + H2PO4−
B HPO42− + H2O → H3O+ + PO43− HPO42− has a high negative charge and so dissociation of it will occur to the least extent.
Under what conditions are gases most soluble? A high P and high T B high P and low T C low P and high T D low P and low T
B high P and low T
Which compound is a weak electrolyte? A. CaCl2 B. H2CO3 C. PbSO4 D. CH3OH
B. H2CO3 All ionic compounds are strong electrolytes, regardless of how soluble they are. This means that both choices A and C can be eliminated. Both carbonic acid and methanol are molecular compounds, but since carbonic acid dissociates to a small extent in solution (it's a weak acid) while methanol doesn't, B is the best answer.
Role of IMF in Physical Properties Pt3: Boiling Point and Freezing Point
BP = is the temperature at which the condensation/vaporization phase transitions occur - L -> G (vaporization) - G -> L (condensation) Boiling point is more specifically when Pvap = Patm
How would you increase the solubility of sugar in water? A increase P B decrease P C increase T D decrease T
C increase T (not related to pressure)
Which of the following best explains why gases behave less ideally at higher pressures? A. Molecules possess greater kinetic energy at higher pressures. B. Molecular collisions become increasingly elastic at higher pressures. C. Molecular interaction occurs to a greater degree. D. As a gas is compressed, its temperature increases.
C. Molecular interaction occurs to a greater degree. At higher pressures, gaseous molecules are packed in closer proximity to one another and intermolecular forces play a larger role, resulting in non-ideal behavior (hi P = low V) an increase in kinetic energy would result in more ideal behavior An increase in the elasticity of collisions would be characteristic of more ideal behavior, not less
What is the final phase of a 36 g water vapor sample at 400°C after removal of 15 kJ of energy? [Note: ΔHfus and ΔHvap = 6.0 kJ/mol and 40.6 kJ/mol, respectively; c of solid, liquid, and gaseous water = 38.0 J/mol?K, 74.5 J/mol?K, and 36.0 J/mol?K, respectively] A. Aqueous B. Solid C. Liquid D. Gas
D. Gas As we are uncertain of the end phase of the water, let us first calculate the amount of energy required to cool the sample to its boiling point. Given q = mcΔT (2 mol)(36.0 J/mol?K)(300 K) = 21,600 J, or 21.6 kJ, which is far more energy than the amount we removed. Thus, no phase change takes place Choice A could have been eliminated before doing any calculations because aqueous is not a phase, but describes a solution in which a solute is surrounded by water.
What is the ratio of the diffusion rates of hydrogen gas to oxygen gas? A. 2 : 1 B. 1 : 2 C. 4 : 1 D. 1 : 4
Diffusion rate is proportional to the speed of the gas. Since lighter gases travel faster than heavier gases, hydrogen must diffuse faster than oxygen. This eliminates 1 : 4 and 1 : 2. Two gases with the same temperature have the same average molecular kinetic energy. Thus, (1/2) mHvH2 = (1/2) mOvO2, which implies (vH/vO)2 = mO/mH. Since mO/mH = 16, we have (vH/vO)2 = 16, which gives vH/vO = 4/1.
Process of Dissolution (dissolving) in Water
Electrolytes dissolve in water steps: 1st = Agitation (stirring, endothermic=bonds breaking) (ex: NaCl) 2nd = Dissociation (endothermic, ions break apart; breaking bonds is endothermic, think S>L>G) (Na+ Cl-) 3rd = Solvation (exothermic=ions form bonds with solvent) **dissolution is only going to occur if the net process is exothermic Polar non-electrolytes dissolve in water steps: 1st = Agitation (endothermic) (ex: C6H12O6) 2nd = Solvation (exothermic) **polar species dissolve much faster Nonpolar non-electrolytes do not dissolve in water steps: 1st = =Agitation (endothermic) (ex:CCl4) **"Like Dissolves Like"**
A mixture of gases at 760 torr contains 50% carbon dioxide, 30% helium, and 20% hydrogen by pressure. What is the partial pressure due to carbon dioxide? A. 532 torr B. 380 torr C. 152 torr D. 228 torr
If half the mixture is composed of CO2, then half the total pressure is due to CO2. Thus, the partial pressure of CO2 is (1/2)(760 torr) = 380 torr.
Condensation
Gas to liquid Heat is released Internal KE decreases Entropy decreases
Electrolytes in Water that are ALWAYS soluble:
Group I ions, H+ (hydrogen ions) NH4+ (ammonium ions) NO3- (nitrate ions) CH3COO- (acetate ions) ClO4- (perchlorates)
Going from a solid to a liquid to a gas
Heat is absorbed (H>0; endothermic) Internal KE increases Entropy increases endothermic processes: - fusion (S -> L) - vaporization (L->G) - sublimation (S->G): requires heat input, this reaction removes heat from its surroundings (lowering the temperature of its surroundings)
Going from a gas to a liquid to a solid
Heat is released (H<0; exothermic) Internal KE decreases Entropy decreases exothermic processes: - condensation (G->L) - crystallization (L->S) - deposition (G->S)
Rank the following species by increasing boiling point. I.CH3CHO II.F2 III.CH3OH IV.KBr
I.CH3CHO (Polar, weaker dipole-dipole) II.F2 (NP = LDFs) III.CH3OH (Polar, can hydrogen bond with OH group) IV.KBr = ionic = strongest (K+ and Cl- full charges) II < I < III < IV
When aqueous solutions of AgNO3 and Ba(OH)2 are combined, one should expect to observe: I. no visible change since all ion combinations create soluble compounds. II. the formation of a precipitate since AgOH is insoluble. III. the formation of a precipitate since Ba(NO3)2 is insoluble.
II. the formation of a precipitate since AgOH is insoluble. The reaction suggested is the double displacement: AgNO3(aq) + Ba(OH)2(aq) → Ba(NO3)2(aq) + AgOH(s). Two common ionic solid solubility rules are that nitrate compounds are soluble, while most Pb, Hg, and Ag solids are insoluble. Because the AgOH forms a precipitate, Roman numeral I is false while Roman numeral II is true. Since all nitrates are soluble, Roman numeral III is also false
An ideal gas fills a closed rigid container. As the number of moles of gas in the chamber is increased at a constant temperature: A. pressure will increase. B. the effect on pressure cannot be determined. C. pressure will decrease. D. pressure will remain constant.
If V, R, and T are constants, then the ideal gas law, PV = nRT, implies that P is proportional to n. Therefore, increasing n will cause an increase in P.
Two gases, each 1 L at STP, are allowed to spontaneously react in an insulated cylinder with a floating piston to form two new gaseous products such that total moles are constant before and after the reaction. Immediately after the completion of the reaction the volume of the cylinder was measured to be 1.82 L. What can be said about the reaction? A. The reaction was isothermal. B. The reaction was endothermic. C. ΔS for the reaction was negative. D. The reaction was exothermic.
If the reaction created the same number of moles of gas as it consumed, and the reaction remained at STP, the volume of the cylinder should have been 2 L. Since the eventual volume is less with the pressure equilibrated to atmospheric, the temperature of the reaction must have decreased, as would have been the case if the reaction was endothermic and consumed heat from the system in order to do chemical work. Had the reaction been exothermic, and the reaction given heat to the system, the end volume would have been greater than 2 L. If the reaction were isothermal, at STP, there would have been no change in volume. Finally, ΔS for the reaction could not have been negative, since the number of moles of gas did not change over the course of the reaction. - The reaction was endothermic. V:T so if V was less than expected, T decreases as with the case of S>L>G THINK OF IT LIKE THIS: n1=n2 (which doesn't follow avogadro's, but v1 < v2 so that means t1 < t2 and since t2 went up the KE went up and the KE increases from s > l > g which is an +H endothermic reaction
Physical changes
Melting, freezing, and boiling - no intramolecular bonds are made or broken; a physical change ONLY affects the intermolecular forces between molecules or atoms - intermolecular forces affected = ion-dipole, H-bonding, dipole-dipole, induced-dipole, LDF - intramolecular forces NOT affected = ionic, covalent, coordinate covalent, metallic ex: ice melting to liquid water does not change the molecules of H2O into something else. Melting reflects the disruption of the attractive interactions between the molecules
gases
Molecules in the gas phase move freely of one another and experience very little, if any, intermolecular forces - gases are the most energetic and least ordered (most entropy) of the phases
Heating Curve (Phase Change)
Potential energy of the substance increases as IMFs break (no temperature change occurs, flat part on graph) - similar to how real gases have IMFs and PE *the pressure is constant (1atm) in a heating curve *heat (q) is required to change the phase of a substance (flat line on graph): q = ndeltaH - flat part on graph = phase change/IMF breaking (q=nH) - slope on graph = temperature change (q=mcT) - can add equations (see notes): qtot=q1 + q2
Boiling Point (relationship: pressure, temperature, IMFs)
Pvap = Patm Trends: - External pressure is directly related to BP (boiling is only going to occur when the independent vapor pressure is the same as the external pressure) (THINK: low atmospheric pressure (high elevation) = lower BP higher atmospheric pressure (low elevation) = higher BP) - IMF is directly proportional to BP (the stronger the IMFs= the longer it takes the vapor pressure to reach the atmospheric pressure and the longer it takes to boil)
Solubility Rules of Solids/Liquids
Solids and Liquid Solutes in Water: - solubility is directly proportional to temperature (higher temperature will increase solubility) - solubility is not affected by pressure (you don't have any particles in gas phase) Gaseous Solutes in Water: - solubility is indirectly proportional to temperature (cold water is better to keep gas particles in solution) (think of hot can of Coke will explode) - solubility is directly proportional to pressure (more O2 gas, will be able to dissolve with greater pressure) (more gas remains dissolved in liquid when pressure is increased, just like unopened soda can)
Solutions =
Solution = Solute + Solvent A solution is a homogeneous mixture of 2 or more substances - the solute is usually present in small quantity - the solvent is usually present in large quantity (solvent is usually water = aqueous solution)
Units of Temperature
T (in K) = T(in celcius) + 273K - this is an absolute temperature scale where 0K = 0 entropy where molecular motion is at a minimum, 0 internal energy = 0 KE - no negative temperatures, always take absolute temperatures
Gram's Law of Diffusion/Effusion (equation?)
The rate of diffusion (gas molecules spreading in container, v) or effusion (molecules passing through/escaping an opening) of a gas is inversely related to the square root of its molar mass (MW) - heavy particles move slowly - light particles move quickly (perfume molecules spread quickly in a room) - lighter MW particles would effuse through a hole faster speed increases as temperature (which is directly proportional to KE) increases rate of effusion = velocity v1/v2 = sqrt(MW2/MW1)
ex of ideal gases
The real gas that acts most like an ideal gas is helium. This is because helium, unlike most gases, exists as a single atom, which makes the van der Waals dispersion forces as low as possible. Another factor is that helium, like other noble gases, has a completely filled outer electron shell - should be the most volatile and have the least IMFs - also should have the smallest molecular volume (n=1 vs n=2) ex: NO2, CO2, and N2O are all elements of 2nd period, while CS2 belongs to the 3rd making it the one to deviate the most from ideal behavior (all have LDFs; otherwise look for IMF trend)
Inside a half-filled water balloon at 25°C and sea level, the vapor pressure of water is 24 mm Hg. What will the vapor pressure of water in the balloon be if a diver takes it to a depth where temperature is 25°C and pressure is 2 atm? WHAT ARE THE VAPOR PRESSURE TRENDS WITH IMF, PRESSURE, TEMP A. Cannot be determined from the given information B. 12 mm Hg C. 24 mm Hg D. 48 mm Hg
The vapor pressure of a substance depends only on the temperature and the intermolecular forces that substance experiences. In particular, it does not depend on external pressure. Therefore, the vapor pressure of water will not change and 24 mm Hg is the correct answer.
Role of IMF in Physical Properties Pt1 : Volume and Pressure (same)
Volume = the space that a gaseous substance occupies - IMF indirectly proportional to V (more space = less interaction between particles) Pressure = the force exerted by gas particles on a surface - IMF is indirectly proportional to P (adding more IMFs causes the molecules to hit each other therefore won't be traveling in container and hitting the sides of the container as much = results in smaller pressure) (less IMFs means particles will hit the walls more often and you will get a larger force)
van der walls equation for real gases; what is 'a' and what is 'b'?
a= strength of intermolecular forces b = molecular size the larger the values of "a" and "b", the larger the deviation from ideal behavior predicted by the ideal gas law
as a solid absorbs heat
as a solid absorbs heat its temperature increases, meaning the avg KE of the molecules increases. This causes molecules to move around more, loosening IMFs and increasing entropy
Every type of molecule...
experiences intermolecular forces such as: - LDFs - dipole interactions - hydrogen bonding all molecules have some degree of attraction towards each other (dispersion forces at least), and its the intermolecular interactions that hold matter together as solids to liquids - the strength and the type of intermolecular forces depend on the identity of the atoms and molecules of a substance: i.e. NaCl(s), H2O(l), and N2(g) = all have different strengths of intermolecular forces and varying melting/boiling points
Phase changes that release heat
condensation, freezing, desposition - phase changes that bring molecules together release heat
Phase changes that absorb heat
fusion, vaporization, sublimation - phase changes that spread molecules out absorb heat
Desposition
going directly from a gas to a solid Heat is released Internal KE decreases Entropy decreases
denver is at a higher altitude than los angles and therefore the atmospheric pressure is lower in denver than in los angles. compared to los angles the melting point of water in denver is a. higher b. lower c. same
higher - on a P vs T phase diagram of water, the solid-liquid equilibrium line has a negative slope for water. Water's melting point increases with decreasing external pressure. Therefore in Denver the melting point of water is higher than in Los Angeles - not asking about BP, BP of denver would be lover than LA
High temperatures
increase the temperature at a given pressure, a solid transforms into a liquid and then into a gas
Density (relationship: pressure, temperature, IMFs)
is a measure of how condensed a substance is - external Pressure is directly proportional to density - external Temperature is indirectly proportional to density (increase volume:T, decrease density) - IMF is directly proportional to density (molecules are held together more tightly, taking up less volume, making it more dense)
Specific heat
is a substances intrinsic property and tells us how resistant it is to changing temperature water: 1 calorie per gram x degree Celsius copper: 0.09 cal/gramxdegreeCelsius
Solubility (S)
is the amount of a substance that can dissolve in a specific solvent at a specific temperature (think about adding sugar to cold glass of iced tea vs. hot glass) Unsaturated solution - concentration of solute Qsp < solubility Ksp (not adding very much sugar in coffee) - additional solute can still dissolve - more reactants, shifts to products Saturated solution - concentration of solute, Qsp= solubility, Ksp - no additional solute will dissolve (can't put any more sugar into coffee) Supersaturated solution - concentration, Qsp > solubility, Ksp - additional solute causes excess precipitate - more products (hi Qsp), will shift to reactants
calorie
is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius - heat is measured in joules 1 cal = 4.2J
Low temperatures
matter tends to exist as a solid and is held together by intermolecular interactions - the molecules don't have enough KE to overcome the intermolecular forces
Sublimation
solid directly to gas Heat is absorbed Internal KE increases Entropy increases
Heat of fusion
the amount of heat that must be absorbed to change a solid into a liquid
Standard Temperature and Pressure (STP)
the conditions under which the volume of a gas is usually measured temp = 0C = 273K pressure = 1 atm (vs. Standard State = 25C = 298K and 1 atm)
Heat of vaporization
the energy absorbed when a liquid changes to a gas
Which of the following is the most likely identity of this white powder (a solid)? A. Na B. H2SO4 C. C3H6O D. NaC3H5O3
we are looking for the compound that will have the strongest intermolecular forces (and therefore is most likely to be solid). - Large mass also contributes to phase: <4-5C (g), 10-15 (l), >20C (s) H2SO4 (sulfuric acid) is capable of hydrogen bonding C3H6O (acetone) is capable of dipole-dipole interaction NaC3H5O3 (sodium lactate) is an ionic compound. Ionic interactions are stronger than any other form of IMF, making NaC3H5O3 the answer While sodium is a metal, pure sodium would not appear as a white powder, nor would it be added to any traditional solution given its volatile reactivity when added to water (choice A is incorrect).
