class 3 General chemistry

In Van der Waals equation what is 'b'

'b' is molecular size

How to solve for, What is the partial pressure of He in a mixture comprised of 2 g He, 32 g O2 and 44 g CO2 at STP

32 g of O2 = 1 mol 2 g of He = 0.5 mol 44 g of CO2 = 1 mol P = 0.5 + 1 + 1 P = 2.5 Xhe = 0.5 He / 2.5 = 0.2 Pressure(partial) = (0.2)(1 atm) = 0.2 atm

which has the highest vapor pressure? A) CH4 B) H2O C) CH3OH D) (CH3)2O

A) CH4 increase of vapor pressure = decrease in intermolecular force

Denver is at a higher altitude than Los Angeles and therefore the atmospheric pressure is lower in Denver than in Los Angeles. Compared to Los Angeles, the melting point of water in Denver will be: A) higher B) lower C) the same D) undetermined from the information given

A) higher On a pressure vs temperature phase diagram of water, the solid-liquid equilibrium line has a negative slope for water. Water's melting point increases with decreasing external pressure

A chemist seals a rigid reaction vessel containing a gaseous reaction at equilibrium and begins pumping in helium gas. She fails to see a change in the relative quantity of reactants and products in the system of study. Which of the following best explains these observations? A. Total pressure has increased with no change in the reaction quotient. B. Total pressure has increased with compensatory changes in Q and Keq. C. Total pressure has decreased with no change in the reaction quotient. D. Total pressure has decreased with compensatory changes in Q and Keq.

A. Total pressure has increased with no change in the reaction quotient.

usually insoluble

Ag^+, Pb^2+, Pb^4+, Hg2^2+, Hg^2+, CO3^2-, PO4^3-, and S^2-

which has the highest freezing point? A) CH4 B) H2O C) CH3OH D) (CH3)2O

B) H2O increase freezing point = increase in IMF

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

How to solve for, A 2 mol sample of He initially at 1 atm and 27 ˚C has its temperature doubled and its volume halved. What is the final pressure of the gas?

PV = nRT P = T / V P (proportional) 2T / 1/2 V = 4P 2 ÷ 1/2 = 4

saturated solution

concentration = solubility. no additional solute will dissolve

what is the dissociation (i) of C6H12O6

i = 1

what is the dissociation (i) of NaCl

i = 2

the pressure of ideal or real gas is more

Pressure (ideal) > Pressure (real)

How to solve for, What is the volume of 0.25 mol He at 25 ˚C and 725 torr?

STP = 0 ˚C at 1 atm 22.4 L per mole (20L)(0.25) = 5 L of He to the 22.4 L per mole and multiplied by the 0.25 given. did not have to worry about the pressure or the temperature

unsaturated solution

concentration < solubility . Additional solute can still dissolve

supersaturated solution

concentration > solubility. additional solute causes excess to precipitate

what is the dissociation (i) of Ca (NO3)2

i = 3

always soluble in water

group I ions, H^+, NH4^+, NO3^-, CH3COO^-, and ClO4^-

which is denser ice or water

ice is denser than water

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

A confined gas at 0°C occupies a volume of 55.6 L. Determine the volume of this quantity of gas if the pressure is held constant but the temperature is lowered to -10°C. A. 42.0 L B. 53.6 L C. 5.56 L D. 33.6 L

B. 53.6 L At constant pressure, the volume drops by a factor of 1/273 for every 1 kelvin (or 1°C) drop in temperature. Thus, the volume here drops by (10 / 273) × (55.6 L) = 2 L, so the final volume is 55.6 - 2 = 53.6 L.

Which of the following substances, when added to a saturated solution containing both aqueous and solid silver chloride, will cause dissolution of the silver chloride solid through complex ion formation with Ag? A. Aqueous silver nitrate B. Aqueous potassium cyanide C. Aqueous sodium chloride D. Aqueous sodium acetate

B. Aqueous potassium cyanide In order to solubilize the solid silver chloride, the aqueous ions must be consumed (Le Châtelier's Principle) causing the equilibrium to shift and dissolve more solid silver chloride. Alternatively, the silver chloride must be converted to a soluble substance, such as a complex ion. Adding neutral salts of silver or chloride is the common ion effect and will actually reduce the solubility of silver chloride, causing more precipitation, not dissolution (eliminate choices A and C). Aqueous potassium cyanide will cause the formation of the complex ion dicyanoargenate, Ag(CN)2- (aq), resulting in the consumption (dissolution) of the solid silver chloride. AgCl(s) + 2 CN-(aq) ? Ag(CN)2-(aq) + Cl-(aq). The addition of sodium acetate will have no effect, since both sodium and acetate salts are known to be completely dissociated in solution (eliminate choice D).

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. A. I only B. II only C. III only D. II and III only

B. II only 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, making B the best answer.

Which of the following changes to an equilibrated system is most likely to change the proportion of reactants and products at equilibrium? A. Increasing activation energy B. Increasing product stability C. Increasing reactant concentration D. Increasing reaction rate

B. Increasing product stability Increasing product stability will increase the relative proportion of products at equilibrium (choice B is correct). Changes in reaction rate (and other kinetic changes) are not likely to impact equilibrium (or other thermodynamic properties - choices A and D are wrong). Increasing reactant concentration will temporarily decrease the reaction quotient, Q, but once equilibrium has been re-established, the same proportions of reactants and products will exist (choice C is wrong).

The ΔG° of a reaction increases following an increase in temperature. What impact would this have on the equilibrium constant? A. It increases. B. It decreases. C. It does not change. D. Inadequate information is provided to determine the outcome.

B. It decreases. As ∆G increases it becomes more positive thus favoring the reactants. SO K = P/R and that number would become smaller, it decreases!

If the first measurements of the ideal gas constant, R, were performed at high altitude instead of at sea level, what would be true of the derived value? A. Magnitude would be greater than 0.08 B. Magnitude would be 0.08 Correct Answer C. Magnitude would be less than 0.08 Your Answer D. Magnitude could not be determined above sea level

B. Magnitude would be 0.08 Correct Answer Assuming the gas behaves ideally, the ideal gas constant is valid and the same at all pressures and temperatures. Looking at the units (L?atm?K-1?mol-1 ) shows that the constant factors in differences in volume, pressure, temperature and number of moles.

Which of the following represents a deviation from the assumptions of the kinetic molecular theory of gases when observed in real gases? A. Kinetic energy is conserved upon collisions. B. Particles are instantaneously polarized. C. Molecules remain in constant random motion. D. The temperature of the gas depends on its average kinetic energy.

B. Particles are instantaneously polarized. The kinetic molecular theory of gases describes the behavior of gases but relies on many assumptions, including: the total volume of gas molecules is negligible, all collisions are elastic (choice A is incorrect), particles are in constant random motion (choice C is incorrect), particles span a distribution of speeds, and gas particles do not interact appreciably (no IMFs). Instantaneous polarization of molecules is characteristic of London dispersion forces and would contribute to deviations from predicted behavior (choice B is correct). Temperature is a function of average kinetic energy of particles and is true of any sample (choice D is incorrect).

Which of the following is NOT a criterion for a gas to be considered ideal? A. The molecules have negligible volume. B. The molecules have negligible mass. C. The molecules do not experience intermolecular forces. D. The molecules do not liquefy at low temperature.

B. The molecules have negligible mass.

The enthalpy of formation of HCl(g) from H2(g) and Cl2(g) is -92.3 kJ/mol. The system was allowed to establish equilibrium for an hour. Which of the following observations is consistent with this? A. The pressure measured at equilibrium is higher than the pressure immediately following the reaction. B. The pressure measured at equilibrium is lower than the pressure immediately following the reaction. C. The temperature measured at equilibrium is higher than room temperature. D. The temperature measured at equilibrium is lower than room temperature.

B. The pressure measured at equilibrium is lower than the pressure immediately following the reaction. After one hour the reaction is at equilibrium and will not be generating any net heat, so the temperature should equal room temperature, eliminating C and D. Because the reaction is exothermic, the gas expands initially, causing the pressure reading to peak. As equilibrium is established, the gas cools and contracts, and the final pressure reading at equilibrium will be lower than the initial peak.

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.

B. The reaction was endothermic. 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.

To increase the solubility of a gas in solution you could: A. stir the mixture. B. cool the mixture. C. move the solution to a higher elevation. D. place it in a container under a vacuum.

B. cool the mixture. Stirring a solution has no impact on how much solute can dissolve in a solvent, although it can affect the rate at which a solute (usually a solid) dissolves (eliminate choice A). At higher elevation atmospheric pressure is lowered. Therefore, choices C and D both suggest the same change and must both be incorrect. The solubility of a gas increases as pressure increases, or as temperature decreases, making B the best answer.

A researcher is working with a sample of neon at a temperature of 285 K and a pressure of 58 atm. If the pressure is lowered to 48 atm, the best prediction would be a phase change from: A. gas to liquid. B. liquid to gas. C. liquid to solid. D. gas to solid.

B. liquid to gas. Changing gas to solid, liquid to solid, or gas to liquid would each involve increasing the pressure of a noble gas. The only transformation listed that involves a decrease in pressure is the change from liquid to gas.

A substance is in the gas phase at STP. As the pressure of the surroundings is progressively decreased at constant temperature, the gas will eventually undergo: A. sublimation. B. no phase change. C. evaporation. D. condensation.

B. no phase change.

Which of the following statements most clearly defines the P and V terms of the van der Waals equation for real gases? A.P is the pressure caused by collisions with the walls of the container and between gas molecules, and V is the volume of the container. B.P is the pressure caused by collisions with the walls of the container, and V is the volume of free space in the container. C.P is the pressure caused by collisions with the walls of the container and between gas molecules, and V is the volume of free space in the container. D.P is the pressure caused by collisions with the walls of the container, and V is the volume of the container.

B.P is the pressure caused by collisions with the walls of the container, and V is the volume of free space in the container.

As a substance goes from the gas phase to the solid phase, heat is: A) absorbed, internal energy decreases, and entry decreases B) released, internal energy increases, and entropy decreases C) released, internal energy decrease, and entropy decreases D) released, internal energy decreases, and entropy increases

C) released, internal energy decrease, and entropy decreases

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? A. Cannot be determined from the given information B. 12 mm Hg C. 24 mm Hg D. 48 mm Hg

C. 24 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.

When 1 mole of K3PO4 is dissolved in 1 L of water, how many moles of ions are produced? A. 1 B. 2 C. 4 D. 8

C. 4 Because potassium phosphate is an ionic compound, it is a strong electrolyte and will dissociate in solution (eliminate choice A). The covalent bonds between the P and O will not break: only the ionic bonds will, so choice D can be eliminated. The question asks for the total number of ions formed, not just the number of different types of ions. Since three K+ ions and one PO43- ion will form for every unit of K3PO4, choice C is the better answer.

A sample of nitrogen gas is cooled from 80°C to 20°C in a rigid-walled container. What impact would this have on pressure? A. Increase to 1.2 times the original pressure B. Increase by a factor of 4 C. Decrease to 0.8 times the original pressure D. Decrease by a factor of 4

C. Decrease to 0.8 times the original pressure Remember!! change celcius to kelvin! it should be p2/p1 = 293/353 = 0.8

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.

Which of the following is true of two solutions heated to 70°C? A. The same amount of energy was required to raise the temperature of each to 70°C. B. The final temperature following mixing of the two solutions would be 70°C. C. All molecules in each solution are traveling at the same speed. D. The solutions possess the same average molecular kinetic energy.

D. The solutions possess the same average molecular kinetic energy. Temperature is a measure of the mean molecular motion in a sample, therefore two samples at the same temperature would possess the same average molecular kinetic energy (choice D is correct). As we do not know the starting temperature, nor the heat capacity of either substance, we cannot determine the amount of energy needed to heat them to 70°C (choice A is incorrect). If the two solutions were mixed, a chemical reaction may occur which could change the final temperature (choice B is incorrect). While the average molecular kinetic energy of the solutions may be the same, this does not mean that every molecule travels at the same speed. Instead, they occupy a distribution of speeds (choice C is incorrect).

What assumption is NOT made when a closed-end manometer is used? A. The gas is behaving ideally. B. The gas is not reacting with the mercury in the tube. C. The gas is not soluble in mercury liquid. D. The vapor pressure of mercury is zero.

D. The vapor pressure of mercury is zero. Whenever you use a manometer, you have to assume that the gas is ideal (choice A), and that the gas is chemically and physically immiscible with mercury (choices B and C). However, since the vapor pressure of mercury is identical over the liquid's surface in the left and right sides of the J-tube, the partial pressure of Hg( g ) cancels itself out, no assumption has to be made.

A balloon contains 3 gasses, O2 , N2 and Xe. At constant temperature which gas exerts the most momentum on the wall of the balloon with each molecular collision A. They all transfer the same momentum per collision Your Answer B. O2 C. N2 D. Xe

D. Xe highest mass

pressure decreases with decreasing

decreasing temperature

vapor pressure is directly proportional to

external T

Boiling point is directly proportional to

external pressure and IMF

density is directly proportional to

external pressure and IMF

melting point/freezing point is directly proportional to

external pressure and IMF

external Pressure has what affect on vapor pressure

external pressure has no effect on vapor pressure

density is indirectly proportional to

external temperature

what volume of NH3 is made from 3 L N2 and 3 L H2 at STP? N2 (g) + 3 H2(g) --> 2 NH3(g)

the molar ratio of N to H is 1 : 3 so for every 1 mole of N we need 3 mol of H. we have 3 L of N so we need 9 L of H2 but we only have 3 L so its the limiting reagent! so we have a ratio of N : 2 NH3 so we end up with 2 L of NH3

when asked the question like, Given starting conditions of -100°C and 1 atm, which of the following changes could potentially result in CO2 fusion? what should you immediately think

think of the phase diagram so to get solid CO2 to melt one would increase the temperature and the pressure. If you decrease the pressure then it will become a gas, you want it to melt not sublime.

According to Boyl's law P is inversely proportional to

volume PV = nRT

according to Charles law T is directly proportional to

volume PV = nRT

according to avagadros law how is volume and molarity related

volume is proportional to moles

how to solve the problem, How much energy is required to convert 18g of 90˚C water to 100˚C steam? - c of H2O (l) = 4.18 J/g ˚C - ∆Hvap(H2O) = 40.68 kJ/mol

you need to include both the temperature change and the phase change so use the formula q = m∆Hvap + mc∆T q = (1)(40.68) + (18)(4)(10) q = 1(40.68) + 800J q = 41 kJ + 800J q = 41.8 kJ

1 atm = ? mmHg

760 mmHg

1 atm = ? torr

760 torr

vapor pressure is indirectly proportional to

IMF

1 atm = ? kPa

101 kPa or 100 for mACT

cm^3 to grams

1cm^3 = 1 g

1 L of H2O = ? moles

about 55

what is fusion also known as

melting

how to find the rate of effusion

1 / √molar mass

1 liter = ? Kg water

1kg or 1000 g

1 mole of ideal gas at STP

22.4 L

The van der Waals equation for real gases: (P + an^2/v^2) (V-nb) = nRT contains two constants which have unique values for each gas. When comparing these constants for neon and argon, the constant "a" is larger for argon because: A. argon has larger particles than neon. B. argon has more protons than neon. Your Answer C. argon has stronger intermolecular forces than neon. D. argon has a greater density than neon.

C. argon has stronger intermolecular forces than neon. he constant "a" is a correction for the attractive forces between the gas molecules. The larger the value of "a," the stronger the intermolecular forces of the gas in question. Only choice C talks about intermolecular forces, so is the correct answer. Choice A, referring to particle size, is dependent on the "b" constant from the equation (eliminate choice A). The number of protons does not have a consistent relationship to intermolecular forces (eliminate choice B). Finally, density (which equals mass/volume) has no correlation to the van der Waals equation (eliminate choice D).

CO(g) + NO3(g) → NO2(g) + CO2(g) The overall reaction order for the elementary step above is: A. zeroth order. B. first order. C. second order. D. third order.

C. second order. The rate law for this elementary step is rate = k [CO][NO3] which, due to each reactant being first order, is a second order process overall (choice C is correct).

Sublimation releases or absorbs heat

absorbs heat because it goes from solid to gas. requires energy so absorbs heat

what will cause precipitate to form

adding common ions

what will cause a solid to dissolve more

adding not common ions

explain triple point

all phases are in equilibrium (NOT equal volumes)

vapor pressure always increases as what increases

as temperature increases

Polar molecules exhibit dipole-dipole interactions, which are intermolecular forces

attractive

How to find the mass of the gas that effuses 4x slower than hydrogen

molar mass (x) = molar mass (H2) (rate (H2)/rate (x) ) ^2 molar mass (x) = 2 g/mol (4)^2 molar mass (x) = 32 g/mol

what solids are typically insoluble

most Pb, Hg, and Ag solids are insoluble

An ideal gas has particles with ? volume compared to their container size

negligible

for gaseous solutes in water, solubility is directly proportional to

pressure

for solid and liquid solutes in water, solubility is not affected by

pressure

light particles move

quickly

heavy particles move

slowly

what size of Keq favors reactants

smallest equilibrium constant (Keq)

typically nitrate compounds are

soluble

In Van der Waals equation what is 'a'

strength of IMF is proportional to 'a'

an ideal gas has an average KE proportional to its

temperature

for gaseous solutes in water, solubility is indirectly proportional to

temperature

for solid and liquid solutes in water, solubility is directly proportional to

temperature