QBank

A

• Ratio of A:B = 2:1
• So, the rate of disappearance of A is 2 x the rate of appearance of B
• Thus, [A]/t = 2 x [B]/t and [B]/t = 0.5 x [A]/t

A 

Normally when more solvent is added, the [] of all species decreases. HOWEVER, this question stem asks about solvent TYPE - changing this will most likely change the activation energy because it will be a completely different reaction!

A

III is not true because, at identical conditions i.e. same Temperature, all species will have the same average Kinetic energy!!

A

Fb = Vfluid displaced x g

The V fluid displaced in this case = the Vbaloon because the entire balloon is submerged in the air. The Methane balloon has the largest volume.

A

• Remember that Keq doesn't always = 1!
• Nothing certain can be said about the [] of the products and reactants OR the rate constant, as that depends on the reaction. 

We can only be sure about the fact that the rate of changes are equal because the ratef = rater

D

If a gas is unideal, the molecules have a volume and they experience intermolecular attractive forces to each other. In this case, since PV/RT < 1, we know that PV is a small value. Considering the Vgas molecules would increase the value of PV, while considering their intermolecular forces will decrease the numerator.

A

Sound will travel faster in denser media. However in this case, we need to take into account the absorptivity of the molecules in air. More massive molecules will absorb more sound, and slow it down. Water (18g) on a humid day will replace N2 (28g) and O2 (32g) in the air. The lessened density will allow sound to travel faster. 

Keep in mind that when comparing different media though, sound travels faster in denser media like solids than in air.

C

This is just a reminder to not forget doubling the distance since the sound must travel first to the bug and then back to the bat.

C

• I is proportional to 1/(d)^2
• By doubling the distance, the Intensity should decrease by a factor of 4. 

So

• db = 10 (log I/Io / 4)
• db = 10(log I/Io) - 10(log 4)
• db = 25 - 6 = 19

B

• 53 x 1 = 53
• 53 x 3 = 159
• 53 x 5 = 265

The harmonics are 1,3,5 meaning that the pipe must be open at one end.

B

v is proportional to sqt(T)

• Remember that increasing T by 44% doesn't mean T = .44!
• The new, increased T will be 1T+.44T= 1.44T

• sqt(1.44T) = 1.2v = 1v + .2v
• So you are increasing v by 20%

D

Intensity: All of the first wave reflects and none of it refracts, so the intensity of wave I will be greater than the intensity of wave II. 

Time: Remember that sound will travel faster in denser media. The second wave travels into the rock and then refracts - the sound speeds up while in the rock and actually travels back in a shorter amount of time than it takes the wave in I to return.

C

An increase by 50db units is a 1 x 10^5 increase in Intensity. 

The different distances are related by their different sqt(intensities) 

sqt(1x10^5) = 1x10^2.5 = 316

D

• T = sqt(L/g)
• What the scientist sees must mean that she observes the g to be greater than what it really is

• mg = T , remember that ma should be added to the lesser valued side
• So, mg = T + ma, meaning that a is pointed in the same direction that T is in.

B

Note that this is an exothermic reaction and when the reaction proceeds in the normal direction, the Pressure increases. 

Increasing the T will shift the rxn to the left, thereby decreasing the mols. So the Pressure will increase, but not by as much as is expected.

C

If the battery's V was increased, the charge would have to be moved through a stronger electric field -- more work 

Increasing the particle's mass will increase the particle's density and its ability to hold more charge - a particle with a greater charge will require more work to be moved through the field.

B

The voltage must be conserved from the anode to the cathode. 

The first resistor will have a Vdrop of 8V, so there are only 4Vs left. Since the next set of resistors are all in parallel, they experience the same Vdrop of 4Vs.

C

The amount of current depends on V and R. Because the V going through that branch of parallel resistors stays the same and because the resistance of the resistors R1 and R2 stay the same, Ohms law states that the current shouldn't change just because R5 is added.

D

The electrons in the pi bond have 100% p character and are unstable - so they are of higher energy. 

The actual bond energy is high because the pi bond combined with the sigma bond makes for a very strong bond which in turn has a high bond energy - this requires more energy to break it. However, this question is asking specifically about the energy of the electrons making up this bond.

D

Since constitutional isomers have different bond to bond connectivity, they will have different functional groups too!

To find the answer, we need to substitute H for Br because it says retention is retained and we know lactic acid is S.

C

Voy^2 = 2hmax x g

C

• Air resistance always acts against the direction of velocity. 
• On the way up, air resistance pushes against the object, so the time and hmax will decrease. 
• On the way down, the air resistance pushes up against the object, so t increases. 

The change in t balances out so t will not change. However, air resistance works in all planes. It will cause the range to decrease.

B

In this case, the football is getting its velocity from the kinetic energy of the kicker's kick - so, the mass of the football does affect its range because a more massive football will have a smaller initial velocity.

D

We're looking for a hill where the angle of acceleration is decreasing. This only happens in hill 3.

C

In oxyacids, the proton is bound to an O atom, so the size of the central atom doesn't matter. 

• However, when normally ranking acidity:
• 1. EN of atom
• 2. Inductive or resonance effects 
• 3. Column - size, Row - EN
• 4. Oxidation (more Os=more acidic)
• 5. Size of atom the proton is bound to

A

Normality = Molarity x equivalents of H ions that the acid can dissociate 

In this case, H3PO4 has 3 protons. So 3 x 1.5M = 3.0 N

C

This question is specifying that the solution is aqueous and at room temperature - so we must also take into consideration the H+ ions that are given from water.

B

Since the object is not 100% submerged, it can be considered to be floating. Thus, mg = Vdispfluid x pfluid x g. Because the gravitational acceleration terms cancel out, gravity will not affect how much of the object is submerged, as long as the fluid in which it is submerged stays the same.

D

Since temperature stays constant, we can assume that a phase change is taking place. During a phase change, any heat applied to a system goes into breaking the intermolecular bonds of the substance to transition to the next phase.

A

A photoelectric cell takes radiation energy in the form of a photon, store it in a battery, and then uses that energy electrolytically.

D

An electrolytic cell doesn't produce energy, it inputs energy in order to run a reaction backwards and store the potential energy.

D

The Nernst equation describes the logarithmic decay of voltage. 

D

Na+ has 10e, giving it the configuration of Ar. However, this question is asking about an excited state of Na+, meaning that the last electron in the 2p6 orbital will move to the 3s subshell.

C

• nisin0i = nrsin0r
• If the media stay the same, increasing the incidence angle must cause an increase in the refracted angle to keep the equation equality