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1
Q

Which has the highest entropy (per mole)?

a. H2O (s)
b. H2O (g)
c. H2O (l)
d. All the same

A

b. H2O (g)

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2
Q

When liquid water freezes below 0 °C…

a. the entropy of the system increases and the entropy of the surroundings increases.
b. the entropy of the system increases and the entropy of the surroundings decreases.
c. the entropy of the system decreases and the entropy of the surroundings decreases.
d. the entropy of the system decreases and the entropy of the surroundings increases.

A

d. the entropy of the system decreases and the entropy of the surroundings increases.

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3
Q

You (a human being) are what kind of system?

a. Open
b. Isolated
c. Closed
d. It depends on whether you are awake or asleep.

A

a. Open

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4
Q

What is the boiling point of methanol, if ΔH° for vaporization is 35.3 kJ/mol, and ΔS° for vaporization is 105 J/mol K?

a. 336 K
b. 2.97 K
c. 373 K
d. 0.33 K

A

a. 336 K

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5
Q

Which of the following would you predict to have the smallest ΔHvap? (The heat required to change one mole of substance from a liquid phase to a gas phase [vaporize]?)

a. CH3OH
b. CH4
c. OF2
d. NaF

A

b. CH4

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6
Q

If you wanted to prepare 500 mL of a 0.20M solution of dextrose (C6H12O6) in water, how much dextrose would you need?

a. 180 g
b. 90 g
c. 36 g
d. 18 g

A

d. 18 g

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7
Q

How would you prepare 500 mL of a 0.20M solution of dextrose (C6H12O6) in water?
a .Put the dextrose in a beaker and add 500 mL of water.
b. Put the dextrose into 0.5 L volumetric flask and add 500 mL of water.
c. Put the dextrose into 0.5 L volumetric flask and add water until the volume of the solution is 500 mL.
d. Fill a 0.5L volumetric flask with water and then add in the dextrose.

A

c. Put the dextrose into 0.5 L volumetric flask and add water until the volume of the solution is 500 mL.

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8
Q

Is Ne or Xe more soluble in liquid water and which of the following best explains why it is the more soluble?

a. Ne, because it is smaller than Xe so it can fit between the water molecules easier which results in stronger interactions.
b. Ne, because it is similar in size to water so that it can replace water molecules easily due to its polarizablity.
c. Xe, because it is larger than Ne and the larger the atom the more soluble it is in water.
d. Xe, because it is more polarizable than Ne resulting in stronger interactions with the water molecules.

A

d. Xe, because it is more polarizable than Ne resulting in stronger interactions with the water molecules.

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9
Q

Which compound do you predict would be most soluble in hexane C6H14?

a. H2O
b. CH3OH
c. CH3CH2OH
d. CH3CH2CH2OH
e. It is not possible to predict solubility from the information given.

A

d. CH3CH2CH2OH

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10
Q

Which of the following must be true about a process where the sign of ΔG is negative?

a. It must be exothermic
b. The entropy of the system must increase
c. The entropy of the universe must increase
d. All are true

A

c. The entropy of the universe must increase

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11
Q

When calcium nitrate is placed in water, the solution becomes clear and the temperature increases. What are the values of ΔH, ΔS and ΔG for this process?

  ΔH    ΔS 	 ΔG

a. + + +
b. – – +
c. – + –
d. + – –

A

c. – + –

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12
Q

Which would be the best solvent for grease (a mixture of hydrocarbons)?

a. toluene (C7H8)
b. ammonia (NH3)
c. molten sodium chloride
d. apple juice

A

a. toluene (C7H8)

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13
Q

Which compounds can form hydrogen bonds with water but not with itself? (Hint: draw out the Lewis structures)

a. CH3OCH3
b. CH3CH2OH
c. CH3CO2H
d. none of them form hydrogen bonds

A

a. CH3OCH3

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14
Q

A high blood alcohol concentration is considered to be 0.25 g/dL. What is the molarity of this blood alcohol (CH3CH2OH) level?

a. 5.4 x 10^–2 M
b. 5.4 x 10^–4 M
c. 115 M
d. 11.5 M

A

a. 5.4 x 10^–2 M

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15
Q

Rank the following compounds in increasing order of solubility when placed in ammonia (NH3):

a. H2O, CH2Cl2, CH4
b. H2O, CH4, CH2Cl2
c. CH4, CH2Cl2, H2O
d. CH4, H2O, CH2Cl2

A

c. CH4, CH2Cl2, H2O

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16
Q

When a solution of CaCl2 is dissolved in water the temperature rises. Which of these statements can definitely be inferred from this observation?

I. The entropy change for this process is negative.
II. The entropy change for this process is positive.
III. The interactions between the species in solution are stronger compared to those in the separate solute and solvent.
IV. The interactions in the separate solute and solvent are stronger compared to those between the species in solution.

a. I and III
b. I and IV
c. II and III
d. II and IV
e. III only

A

e. III only

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17
Q

The entropy change when carbon dioxide (CO2(g)) dissolves in water is:

a. Positive, because mixing things up always increases the entropy since there are more available positions.
b. Negative, because the number of positions available to the carbon dioxide molecules decreases.
c. Zero, because carbon dioxide does not dissolve in water.
d. Either positive or negative depending on the temperature.

A

b. Negative, because the number of positions available to the carbon dioxide molecules decreases.

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18
Q

Ethanol has a boiling point of 78°C and a melting point of -114°C. What happens when ethanol goes from -84°C to 90°C?

a. the entropy of the system decreases and the entropy of the surroundings decreases.
b. the entropy of the system decreases and the entropy of the surroundings increases.
c. the entropy of the system increases and the entropy of the surroundings increases.
d. the entropy of the system increases and the entropy of the surroundings decreases.

A

d. the entropy of the system increases and the entropy of the surroundings decreases.

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19
Q

Consider the following reaction for the synthesis of ammonia.

N2+ 3 H2→ 2 NH3	           
∆H = -92.2 kJ/mol 
∆S = -72.6 J/K

At 25 °C, would this reaction be thermodynamically spontaneous?

a. No because ∆G is positive
b. No because ∆G is negative
c. Yes because ∆G is positive
d. Yes because ∆G is negative

A

d. Yes because ∆G is negative

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20
Q

Why don’t oil and water mix?

a. Because oil is nonpolar and water is polar.
b. There are no attractive forces between oil molecules and water molecules; therefore, the hydrogen bonds between water molecules would require too much energy to break.
c. The entropy of the system is higher in the unmixed state because non-polar molecules cause water molecules to cluster around them.
d. Oil and water repel each other because they both contain negative polar regions.

A

c. The entropy of the system is higher in the unmixed state because non-polar molecules cause water molecules to cluster around them.

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21
Q 
26.	Calcium phosphate (Ca3(PO4)2) is insoluble in water.  The ΔH for solution is about zero.  Predict the signs of ΔS and ΔG.
		ΔS 	 ΔG
a.		+	–
b.		–	–
c.		+	+
d.		–	+
A

d. – +

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22
Q

If you place a container of a mixture of liquid water and water vapor (the system) on a hotplate:
When the hotplate temperature is above 100 °C what change will occur in the system?

A

The liquid water will vaporize since the temperature is above the boiling point of water.

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23
Q

What is the sign of these thermodynamic functions for this change:

a. ΔH system:
b. ΔH surroundings:
c. ΔS system:
d. ΔS surroundings:
e. ΔG:

A

a. ΔH system: (+)
b. ΔH surroundings: (-)
c. ΔS system: (+)
d. ΔS surrounding: (-)
e. ΔG: (-)

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24
Q

If you place a container of a mixture of liquid water and water vapor (the system) on a hotplate:
At T= 100 °C (373K) what is ΔG?

A

ΔG = 0 (because the system will be at equilibrium)

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25
Q

When a hot block is placed next to a cold block the two blocks eventually end up at the same temperature. Explain both how this happens (what processes allow this to occur) and why this happens (and why it will not reverse).

A

Energy is transferred from the hot block to the cold block until the two have the same number of energy quanta.

HOW: Energy is transferred by collisions of metal atoms. When the blocks touch energy can be transferred from hot to cold, then collisions within the block allow the energy quanta to disperse.

WHY: There are more energy states available (arrangements of energy quanta) when the two blocks are at the same temperature (have equal #s of energy quanta) than if one block is hot and one is cold.
That is the entropy is higher (more possibilities for energy states) when the temperatures are the same.

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26
Q

Describe how you would make 250 mL of a 1.25 M solution of sodium chloride, given a 250 mL volumetric flask, water, sodium chloride and a balance.

A

Put 14.6 g NaCl into a 250 mL volumetric flask and fill to the measuring line with water until the bottom of the meniscus reaches the line.

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27
Q

Calculate the amount of sodium chloride needed to make 250 mL of a 1.25 M solution of sodium chloride.

A

250 mL x (1.25 mol NaCl/1000mL) x (58.5 g NaCl/1mol NaCl) = 14.6 g NaCl in 250 mL of water.

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28
Q

When magnesium chloride is added to water, the white solid seems to disappear and the temperature increases. What information can you deduce from these observations? For example about the thermodynamic functions ΔH, ΔS and ΔG, and the relative strengths of interactions

A

MgCl2 + H2) -> MgCl2(aq)
Magnesium chloride dissolves.
Before solution there are ionic interactions in MgCl2 and H-bonding, dipole-dipole, and LDFs in the water.
After the solution forms, there are ion-dipole interactions. Sine the temperature goes up, energy is released to the surroundings. Therefore the interactions after the solution is formed bust be stronger than the interactions before.
ΔH: (-)
ΔG: (-) since MgCl2 dissolved
ΔS: don’t know, probably (+)

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29
Q

Imagine a reaction in which compound A (which is a blue compound) reacts with compound B (which is a yellow compound) to give AB.
A2 + B2 -> 2AB

What can you say about the color of compound AB?

A. It is blue
B. It is yellow
C. It is green
D. It is impossible to predict what the color of AB is from the information given.

A

D. It is impossible to predict what the color of AB is from the information given.

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30
Q

Which acid is the strongest?

a. CH4
b. OH2
c. NH3
d. HF

A

d. HF

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31
Q

When a bond forms between two atoms
A. energy is released to the surroundings
B. energy is absorbed from the surroundings
C. energy is neither created nor destroyed
D. the kinetic energy of the system falls

A

A. energy is released to the surroundings

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32
Q

Which is the strongest base?

a. -CH3
b. -OH
c. -NH2
d. F-

A

a. -CH3

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33
Q

Explain why -CH3 is the strongest base out of

-CH3, -OH, -NH2, and F-

A

-CH3 is the strongest base b/c its the least stable and therefore the most reactive. The negative charge on the carbon is not very electronegative. Carbon has the lowest effective nuclear charge and therefore the least able to stabilize the extra negative charge by interactions with the positive charge by interactions with the positive charge on the nucleus. CH4 (conjugate acid) is the weakest.

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34
Q

Which is a stronger acid, NH3 or H2O?
A. NH3, because N is more electronegative than O, and therefore is better able to stabilize the charge on the conjugate base
B. NH3, because N is less electronegative than O, and therefore is better able to stabilize the charge on the conjugate base
C. H2O, because O is more electronegative than N, and therefore is better able to stabilize the charge on the conjugate base
D. H2O, because O is less electronegative than N, and therefore is better able to stabilize the charge on the conjugate base

A

C. H2O, because O is more electronegative than N, and therefore is better able to stabilize the charge on the conjugate base

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35
Q

When this reaction occurs :
H2O + NH3 ->  –OH + NH4+
Do you think the final reaction mixture contains:

A. More reactants than products because H2O + NH3 are weaker acids and bases than –OH + NH4+
B. More reactants than products because H2O + NH3 are stronger acids and bases than –OH + NH4+
C. More products than reactants because H2O + NH3 are weaker acids and bases than –OH + NH4+
D. More products than reactants because H2O + NH3 are stronger acids and bases than –OH + NH4+

A

A. More reactants than products because H2O + NH3 are weaker acids and bases than –OH + NH4+

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36
Q 
What is the pH of a 0.10 M solution of HNO3?
A. 0.10				
B. 13.0
C. 2.0
D. 1.0
A

D. 1.0

37
Q 
What is the pH of a 0.10 M solution of KOH at 25°C?
A. 0.10				
B. 13.0		
C. 2.0
D. 10
A

B. 13.0

38
Q 
If the pH of a 0.020 M acid is 1.70 what does that tell you about the acid?
I. The acid is completely ionized
II. The acid is strong
III. The acid is not completely ionized
IV. The acid is weak

A. I
B. III
C. I, II
D. III, IV

A

C. I, II

39
Q 
What is the percent ionization in a 0.10 M solution of an acid that has a pH of 3.75?
A. 1.78 x 10^–4 %	
B. 17.8 %		
C. 0.178 %
D. 1.78 x 10^–3 %
E.  1.78 %
A

C. 0.178 %

40
Q 
What is the oxidation number of C in H2CO3?
A. +4		
B. +2
C. -4
D. -3
A

A. +4

41
Q 
In the reaction Zn + Cu2+ -> Cu  + Zn2+
The zinc
a. is oxidized in the reaction
b. is reduced in the reaction
c. is metabolized
d. is a catalyst
A

a. is oxidized in the reaction

42
Q

Which reaction is NOT a redox reaction:

a. 2Na + 2H2O -> 2NaOH + H2
b. H2 + O2 ->  H2O
c. H+ + H2O -> H3O+
d. 2Fe + 3S -> Fe2S3

A

c. H+ + H2O -> H3O+

43
Q

Explain for each reaction how you know it is, or is not, a redox reaction.

a. 2Na + 2H2O -> 2NaOH + H2
b. H2 + O2 ->  H2O
c. H+ + H2O -> H3O+
d. 2Fe + 3S -> Fe2S3

A

a. Is a redox reaction because oxidation number of sodium changes from 0 (Na) to +1 in NaOH and H changes from +1 in H2O to 0 in H2
b. Oxidation numbers change: H from 0 to +1 and O from 0 to -2
c. No oxidation changes. H stays +1 and O stays -2
d. Fe changes from 0 to +3 and S from 0 to -2

44
Q 
In nitric acid, HNO3, the formal charge and oxidation number on the N are:
A.  +1, +5
B.  +1, –3
C.  +1, +3
D.  –1, +5
A

B. +1, –3

45
Q

If the bond dissociation energies of the products are less than the bond energies of the reactants what does this mean in terms of the energy change in the reaction.
A. The reaction is exothermic
B. The reaction is endothermic
C. There is no overall energy change because energy can neither be created nor destroyed
D. It depends on the temperature

A

B. The reaction is endothermic

46
Q

What is the enthalpy change for the reaction:

CH4 + 2Br2 -> CH2Br2 + 2 HBr

A. – 184 kJ
B. + 184 kJ
C. –76 kJ
D. + 76 kJ

A

C. –76 kJ

47
Q

What mass of sodium hydroxide would be required to react with 50 mL of 0.15 M HCl?

NaOH(s) + HCl(aq)  -> NaCl(aq) + H2O(l)

A. 7.5 x 10–3 g
B. 7.5 g
C. 3.0 g
D. 0.30 g

A

D. 0.30 g

48
Q

Is Ne or Xe more soluble in liquid water and which of the following best explains why it is the more soluble?
A. Ne, because it is smaller than Xe so it can fit between the water molecules easier which results in stronger interactions.
B. Ne, because it is similar in size to water so that it can replace water molecules easily due to its polarizablity.
C. Xe, because it is larger than Ne and the larger the atom the more soluble it is in water.
D. Xe, because it is more polarizable than Ne resulting in stronger interactions with the water molecules.

A

D. Xe, because it is more polarizable than Ne resulting in stronger interactions with the water molecules.

49
Q

The entropy change when carbon dioxide (CO2(g)) dissolves in water is:

A. Positive, because mixing things up always increases the entropy since there are more available positions.
B. Negative, because the number of positions available to the carbon dioxide molecules decreases.
C. Zero, because carbon dioxide does not dissolve in water.
D. Either positive or negative depending on the temperature.

A

B. Negative, because the number of positions available to the carbon dioxide molecules decreases.

50
Q

For the reaction of acetic acid (CH3COOH) and water. What products do you expect?

A

CH3COOH + H2O -> CH3COO- + H3O+

51
Q

If the pH of a 0.10 M solution of acetic acid is about 2.9, what does that tell you about the extent of the reaction between acetic acid and water?

A

If acetic acid were a strong acid (fully ionized in water), the pH would be 1 for a 0.1 M solution. Since the pH is 2.9, this means not all of the acetic acid is ionized.
[H30+] = 10^-pH
[H3O+] = 10^-2.9 = 0.00125 M = 1.3 x 10^-3M

52
Q

If the pH of a 0.10 M solution of acetic acid is about 2.9, what is the % ionization of the acetic acid in water?

A

% ionization = (amount ionized / total concentration) x 100
Amount ionized = [H3O+]
(10^-2.9 / 0.1) x 100 = 1.258%

53
Q

Why do we use multiple models of acid-base reactions? Why don’t we just pick one and stick with it?

A

We use models that can help us predict and explain outcomes. Generally we use the simplest model that will work in a given situation. So while all acid base reactions can be described using the Lewis model (a base is an electron pair donor and an acid is an electron pair acceptor), sometimes it is simpler and easier to use the Bronsted-Lowry acid base model (where an acid is a proton donor and a base is a proton acceptor). This is particularly true for reactions in aqueous solution where proton transfer from acid to base is the easiest way to think about the reaction.

(Arrhenius acid base models are pretty useless because they are not widely applicable.)

54
Q

What is the difference between an acid-base reaction and a redox reaction? Use examples of each to illustrate your answer.

A

Acid base reaction: Bonds are formed and broken and a proton is transferred, but NO electrons are transferred between atoms. The oxidation number of each atom remains the same.

In contrast in
2Na(s) + H2O  2Na+(aq) + -OH (aq) + H2(g)
the Na starts with an electron and a zero oxidation number, but ends up as Na+ (+1 oxidation number). It has lost an electron and been oxidized. The hydrogen has been reduced (from +1 in H2O to zero in H2).

55
Q

Calculate the enthalpy change for this reaction

C2H5OH + 3 O2-> 2 CO2+ 3 H2O.

A

Bonds broken = 1 C-C, 5 C–H, 1 C–O, 1 O–H, 3 O=O
Bonds formed = 4 C=O (in CO2), 6 O-H

Bonds broken = (347 + 5(414) + (351) + (464) + 3(498)) = 4726 kJ
Bonds formed = (4(803) + 6(464) = 5996 kJ

Enthalpy change = Σ (bonds broken) – Σ (bonds formed)

= – 1270 kJ

56
Q

Explain the energy change that occurs in an exothermic reaction in part a by discussing the strength of forces and interaction present in the reactants versus products.

A

The reaction is exothermic – which means that energy is released to the environment. The bonds in the products (CO2 and H2O) are stronger than those in the reactants. That is, less energy is required to break the bonds in the reactants than is released in the products.

The bonds are formed by electrical attractions of electrons of one atom to the nucleus of the other – this means that the forces of attraction between the atoms in the products are higher than the forces of attraction between the reactants (meaning that the bonds in the products stronger)

57
Q

The actual enthalpy change is somewhat different to the one that could be calculated – why do you think that might be?

A

Bond energies are calculated or measured in the gas phase. Most reactions do not take place in the gas phase – usually they are in a solvent – and interactions with the solvent can make bond breaking easier. Solvents may also stabilize either the product or the reactants by interactions (solvation)

58
Q

Which reaction do you think has a larger rate constant (faster rate)?
I. HCl + H2O -> H3O+ + –Cl
II. CH3Br + –OH  -> CH3OH + Br–

A. I, because acid base reactions don’t have a high activation energy, since the H being transferred is partially ionized.
B. I, because HCl is a gas, and therefore can react very quickly
C. II, because there is a C-Br bond breaking in the rate determining step
D. II, because hydroxide is a strong base

A

A. I, because acid base reactions don’t have a high activation energy, since the H being transferred is partially ionized.

59
Q

What could affect both the rate of a reaction and the equilibrium constant?
I. change in temperature
II. change in concentrations of reactants
III. presence of a catalyst

a. I and II
b. I
c. I and II
d. All of them

A

b. I

60
Q

Explain what effect each answer
I. change in temperature
II. change in concentrations of reactants
III. presence of a catalyst
has on the rate and equilibrium constant.

A

I. increasing T will increase the rate (more energetic collisions) and the value of K.

II. will only increase the rate (it will change the position of equilibrium – but NOT the K)

III. increases rate – but not K. A catalyst provides an alternate path.

61
Q 
For a reaction A + 2B -> C the rate of reaction Δ[A]/Δ[t] is related to the rate in terms of B by  
A.	Δ[B]/Δ[t]
B. 	2 Δ[B]/Δ[t]
C.	½ Δ[B]/Δ[t]
D. 	it is not possible to determine
A

C. ½ Δ[B]/Δ[t]

62
Q

For the reaction A + B -> C the rate equation is: rate = k[A]2[B]
if the concentration of A is doubled and the concentration of B is doubled, by what factor will the rate increase?
A. 4
B. 2
C. 8
D. 16

A

C. 8

63
Q 
A radioactive tracer Tc has rate constant for decay of 1.05 x 10–2 hr–1. What is the half-life for the decay?
A. 	66 hours
B. 	66 days
C.  	0.693 hrs
D. 	0.480 hrs
A

A. 66 hours

64
Q

What is the equilibrium constant expression for the following equilibrium?
3Fe(s)+4H2O(g)-> Fe3O4(s)+4H2(g)
A. K=[H2]4
B.K=[H2] /[H2O]
C.K=[H2]^4 /[H2O]^4
D.K=[Fe2O3][H2]^4 / [Fe]^3[H2O]^4

A

C.K=[H2]^4 /[H2O]^4

65
Q

If the pH of a 0.15 M acid is 3.6, what is the Ka?

a. 1.2 x 10^-3
b. 2.5 x 10^-4
c. 4.2 x 10^-7
d. 1.0 x 10^-10

A

c. 4.2 x 10^-7

66
Q 
If the pH of a 0.15 M acid is 3.6, what is the % ionization of this acid?
A.	0.80%
B.	0.17%
C.	99.9%
D.	1.07%
A

B. 0.17%

67
Q 
For a system at equilibrium
A.	ΔG = 0
B.	ΔG° = 0
C.	Both ΔG and ΔG° = 0
D.	None are true
A

A. ΔG = 0

68
Q

The equilibrium constant for a reaction
A + B -> 2C is 1.0. If a 1 L solution containing 10 mol A, 2 mol B and 10 mol C is allowed to react, will the concentration of A when equilibrium is reached be:
A. > 10 M
B.

A

A. > 10 M

69
Q

Calculate the pH of a solution of 0.10 M hydrogen cyanide HCN? (Ka = 4.9 x 10-10)

a. 9.31
b. 5.15
c. 4.16
d. 1.00

A

b. 5.15

70
Q

Consult the table of pKas to help you determine whether this reaction would have more products or reactants at equilibrium

NH4+  Cl–  +  H2O  ->  H3O+  Cl–  + NH3

A. Reactants
B. Products
C. Equal amounts
D. Can’t tell from this information

A

A. Reactants

71
Q

Which statement is true for the following reaction at equilibrium?
3H2(g) + N2(g) ⇌ 2NH3(g)

A. All the reactants have been converted to products.
B. The forward reaction has stopped so no more ammonia is formed.
C. The rate of the forward reaction is equal to the rate of the back or reverse reaction.
D. There is no more energy for molecules to get over the activation energy barrier.

A

C. The rate of the forward reaction is equal to the rate of the back or reverse reaction.

72
Q

What is the age of bottled wine that has a tritium (H-3) content that is 60% of the tritium in freshly bottled wine. Tritium decays by beta decay and has a half-life of 12.3 yr.

31H → 32He + 0-1β

A.	0.029 yr
B.	7.4 yr
C.	9.1 yr
D.	16 yr
E.	35 yr
A

C. 9.1 yr

73
Q

The reaction of CH3Br with -OH has a rate equation: rate = k[CH3Br][-OH]. What does this tell you about the mechanism of the reaction? I.e. the sequence of events at the molecular level that leads from reactants to products.

A

Both CH3Br and -OH are in the rate determining step of the reaction. Therefore, it is likely that this reaction has only one step that involves both reactants.

74
Q

Explain why reaction rates depend on concentration of reactants.

A

For a reaction to occur, the reactant molecules must collide The more molecules there are per unit volume, the more likely the are to collide

75
Q

Explain why reaction rates depend on the temperature.

A

The reactant molecules must have enough energy to get over the activation energy (Ea) barrier. This is where bond breaking happens, which requires energy). The high the temperature, the more kinetic energy the molecules have and therefore the more energy of collision.

76
Q

Explain why reaction rates depend on the type of reaction

A

The rate depends on the activation energy which depends on bonds broken and formed. For example, acid-base reactions are fast because the bond to the acidic H is already partially broken. But, to break a C-C bond, a lot of energy is needed, so the reaction is slow.

77
Q

Explain why reaction rates depend on the presence of a catalyst

A

A catalyst provides an alternate pathway with (usually) lower activation energy. For example, in enzyme-substrate complexes the bonds are “loosened” so they take less energy to break

78
Q

For the reaction:
N2(g) + 3H2(g) -> 2NH3(g)
ΔH = +65 kJ
What effect would adding ammonia have on the position of the equilibrium.

A

Would shift the equilibrium to the left.

Would increase the rate of the reverse reaction so more reactants would form.

79
Q

For the reaction:
N2(g) + 3H2(g) -> 2NH3(g)
ΔH = +65 kJ
What effect would increasing the pressure have on the position of the equilibrium.

A

Would shift the equilibrium to the right. Same effect as increasing the concentration of reactants. So there are more collisions and the rate of the forward reaction is increased.

80
Q

For the reaction:
N2(g) + 3H2(g) -> 2NH3(g)
ΔH = +65 kJ
What effect would increasing the temperature have on the position of the equilibrium.

A

Would shift the reaction to the right. This reaction is endothermic. Adding energy will increase the probability of the reactant molecules having enough energy to get over the activation energy barrier.

81
Q

For the reaction:
N2(g) + 3H2(g) -> 2NH3(g)
ΔH = +65 kJ
What effect would adding a catalyst have on the position of the equilibrium.

A

No change.

A catalyst provides an alternate pathway but the energies of the reactants and products stays the same.

82
Q

For the reaction:
N2(g) + 3H2(g) -> 2NH3(g)
ΔH = +65 kJ
What effect would adding helium have on the position of the equilibrium.

A

No change.

Helium is not a component of the reaction.

83
Q

When acetic acid (CH3COOH) reacts with water what is happening, at the molecular level.

A

The OH bond in the acetic acid is breaking. The H from the OH bond in the acetic acid, goes to the water molecule and accepts the electrons making water have a positive charge. The electrons from the OH bond in acetic acid remains on the O creating a negative charge on the oxygen.

84
Q

Why does acetic acid (CH3COOH) reacts with water.

A

The acetic acid acts as an acid and donates a proton (accepts electrons). The water acts as a base and accepts a proton (donates electrons). Collisions have to occur in order to the reaction to happen.

85
Q

Bromoacetic acid (BrH2CCOOH) ionizes in water. What is the percent ionization in a 0.25 M solution of bromoacetic acid that has a pH of 1.6?

A

% ionized = (amount ionized / concentration) x 100

[H3O+] = 10^-1.6 = 0.02511

100 x (0.02511/0.25) = 10.0475

10.05%

86
Q

Bromoacetic acid (BrH2CCOOH) ionizes in water. The percent ionization is 10.05%. It is a 0.25 M solution of bromoacetic acid that has a pH of 1.6. Is this a weak or strong acid? Why?

A

Weak acid.

A strong acid would have a 100% ionization.

87
Q

Consider the reaction A -> B with an initial concentration of [A] = 6.0 M and an equilibrium constant K = 0.5. What are the concentrations of A and B at equilibrium?

A 
K = [B] / [A]
K = [2] / [4] = 0.5
[A] = 4
[B] = 2
88
Q

The Ka for formic acid is 1.7 x 10^-4. What does the Ka tell you about the relative amounts of formic acid and formate ion (the conjugate base) at equilibrium?

A

K

89
Q

What should happen to the pH of a 1.0 M formic acid solution if you added some sodium folate (the conjugate base of formic acid) to the solution? Why?

A

Increase.
The reaction would go to the left because Le chatelier’s principle. Less hydronium ions would make the solution less acid, the pH would go up.
pH = -log[H3O+]
decrease of [H3O+] ions

Chemistry 142 (3 decks)

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