Old Exams Flashcards
- Methane gas burns in a furnace to produce carbon dioxide gas and water in the liquid state. What are the signs of ΔH, ΔS, and ΔG for this process?
a. ΔH = - , ΔS = -, ΔG = +
b. ΔH = - , ΔS = +, ΔG = -
c. ΔH = + , ΔS = -, ΔG = +
d. ΔH = + , ΔS = +, ΔG = -
e. ΔH = - , ΔS = -, ΔG = -
e. ΔH = - , ΔS = -, ΔG = -
A reaction takes place within a system. As a result, the entropy of the system decrease. What must be true?
I. The reaction is exothermic
II. The entropy of the universe increases
III. The entropy of the surroundings increases
IV. Gibbs free energy of the system decreases
A. II and IV
B. II, III and IV
C. II and III
D. All are true
D. All are true
Why does a mixture of dye and water never “unmix”?
a. The process is irreversible
b. The entropy is too high
c. The dye and water molecules have more possible arrangements
d. The process is exothermic
c. The dye and water molecules have more possible arrangements
Which process is exothermic? I. Evaporation of a liquid II. Braking a hydrogen molecule into hydrogen atoms III. Freezing water a. II b. III c. I d. I and II e. I and III f. II and III
b. III
What is the concentration of Na+ ions in a 0.20M solution of Na3PO4?
a. 0.067 M
b. 0.20 M
c. 0.60 M
d. 0.90 M
c. 0.60 M
Ammonia solution is normally diluted for household use. What is the concentration of an ammonia solution prepared by taking 100 mL of 6.50 M ammonia and adding it to enough water to make 2.00 L of solution?
a. 0.130 M
b. 0.325 M
c. 0.650 M
d. 2.08 M
b. 0.325 M
Ice is produced when liquid water freezes. What conditions would be most likely to produce ice?
Claim:
I. Low temperature
II. High temperature
Reasoning
III. The entropy is negative so the process always happens
IV. Both enthalpy and entropy changes are negative so the temperature must be low
V. Both enthalpy and entropy changes are positive so the temperature must be high
a. I and III
b. II and III
c. I and IV
d. II and IV
e. I and V
f. II and V
c. I and IV
What stays the same when a solution is diluted? I. Moles of the solvent II. Volume of the solvent III. Moles of the solute IV. Concentration of the solution a. III b. I and II c. I, II, and IV d. II and IV e. III and IV f. all stay the same
a. III
How would you prepare a 500 mL solution of a 0.25M solution of NaCl?
a. Add 7.3 g NaCl to 500 mL water in a beaker
b. Add 7.3 g NaCl to 500 mL water in a volumetric flask
c. Add 7.3 g NaCl to 500 mL volumetric flask and make the volume up to 500 mL with water.
d. Add 0.25 g NaCl to a 500 mL graduated cylinder and make the volume up to 500 mL with water
c. Add 7.3 g NaCl to 500 mL volumetric flask and make the volume up to 500 mL with water.
Which compound can form hydrogen bonds with water but not with itself? I. CH3OCH3 II. NH2NH2 III. CH3NO2 a. I and II b. II and III c. I, II, and III d. I and III
d. I and III
The boiling point of ethanol is 352 K. What is true about Gibbs free energy at the boiling point?
a. ΔG is positive
b. ΔG is negative
c. ΔG is equal to zero
c. ΔG is equal to zero
Which compound would be the most soluble in hexane (C6H14)?
a. H2O
b. C8H18
c. CH3OH
d. None are soluble in hexane
b. C8H18
Silver chloride AgCl is insoluble in water. The ΔH for the solution is about zero. Which of these statements must be true?
a. The entropy would increase if Ca3(PO4)2 dissolved in water
b. The entropy would decrease if Ca3(PO4)2 dissolved in water
c. The enthalpy change would increase if the water were heated up
d. The enthalpy change would decrease if the water were heated up
b. The entropy would decrease if Ca3(PO4)2 dissolved in water
Why does a solution of sodium chloride conduct electricity, while a solution of sugar does not?
I. Because electrons can flow more easily through a NaCl solution
II. Because sugar molecules are neutral and cannot carry charge to the electrodes
III. Because NaCl ionizes in solution and the ions can carry charge to the electrodes
a. I
b. I and II
c. I, II, and III
d. II and III
c. I, II, and III
When a salt dissolves in water the temperature of the solution drops. Which of these statements can be inferred from this information?
I. The entropy change for this process is negative
II. The interactions between the species in solution are weaker than those in the separate solute and solvent
III. The interactions between the species in solution are stronger than those in the separate solute and solvent
IV. the entropy change for this process is positive.
a. I
b. I and III
c. II and IV
d. I and II
e. III and IV
c. II and IV
Why don’t oil and water mix?
a. Because oil is non polar and water is polar
b. The entropy of the system is high in the unmixed state because non-polar molecules cause water molecule to cluster around them
c. 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
d. Oil and water repel each other because they both contain negative polar regions
b. The entropy of the system is high in the unmixed state because non-polar molecules cause water molecule to cluster around them
When water boils, what bonds and/or interactions are overcome?
Hydrogen bonds, dipole-dipole, LDFs are overcome when water boils
Explain the mechanism by which energy is transferred at the molecular level during the heating process of water.
Bonds are breaking as H2O temp increases which absorbs energy from the surroundings. Energy is transferred through collisions and transfer of quanta. Quanta disperses. Breaking bonds takes energy.
What are the signs of thermodynamic functions for this change:
a. ΔH system
b. ΔH surroundings
c. ΔS system
d. ΔS surroundings
e. ΔG
a. ΔH system (+)
b. ΔH surroundings (-)
c. ΔS system (+)
d. ΔS surroundings (-)
e. ΔG (-)
Explain the mechanism by which energy is transferred at the molecular level during the mixing process.
Collisions. When atoms collide energy is transferred.
The temperature in the beaker increases when LiI and H2O mic, what interactions are being overcome and/or formed?
Ionic bonds between LiI are overcome hydrogen bonds, LDFs, and dipole-dipole are over come in H2O. Ionic interactions formed between Li and O and I and H are formed.
Using these interactions explain why the temperature increases upon mixing LiI and H2O.
Bond making releases heat.
Bond breaking absorbs heat
The interactions that were formed were stronger than the interactions that were overcome.
Which do you think is more soluble in water: O2 or He?
a. He because it is smaller and can fit between the water molecules better
b. He because it is small and highly charged and so will attract the water molecules better
c. O2 because it is the right size to fit in the cavities in the water
d. O2 because it is more polarizable and can form stronger interactions with the water molecules
d. O2 because it is more polarizable and can form stronger interactions with the water molecules
Two toxic substances react to make a new substance. What can you determine about the toxicity level of the new substance?
a. The new substance will be more toxic
b. the new substance would have the same toxicity as the two substances that react
c. The new substances will be harmless
d. You cannot determine if the new substance will be toxic or harmless
d. You cannot determine if the new substance will be toxic or harmless
What features are always present in a base?
I. The presence of an -OH (hydroxide) group
II. The presence of a lone pair of electrons on the basic atom in the molecule
III. The basic atom in the molecule is highly electronegative
a. I only
b. I and II
c. I and III
d. II and III
e. I, II, and III
d. II and III
What factors are important when determining the strength of the acid (HX)?
I. The bond strength H-X
II. The entropy change associated with the reaction where HX donates a proton to water
III. The strength of the conjugate base X-
IV. The heat capacity of the acid
a. I and II
b. I and III
c. I, II, and III
d. I, II, III, and IV
c. I, II, and III
Why in NH4+ a stronger acid than NH3?
a. Because nitrogen is electronegative and can accept electrons
b. Because NH4+ has more protons to donate
c. Because NH4+ has a weaker conjugate base
d. Because NH4+ has a stronger conjugate base
c. Because NH4+ has a weaker conjugate base
Which is a stronger base in water? CH3O-, or CH3COO-
a. CH3O-, because the negative charge is localized on the oxygen, making the species less stable and therefore a better proton acceptor
b. CH3O-, because the negative charge is de-localized on the oxygen, making the species more stable and therefore less likely to accept a proton
c. CH3COO-, because the negative charge is de-localized over the two oxygens, making the species more stable and therefore less likely to accept a proton
d. CH3COO-, because the negative charge is localized on one of the two oxygens, making the species less stable and therefore a better proton acceptor
a. CH3O-, because the negative charge is localized on the oxygen, making the species less stable and therefore a better proton acceptor
Which reaction(s) are redox reaction(s)? I. CH3Br + -OH -> CH3OH + Br- II. H+ + H2O -> H3O+ III. H2 + O2 -> H2O IV. 2 Na + 2H2O -> 2 NaOH + H2 a. I only b. I and II c. III and Iv d. I, II, and III
c. III and IV
If the pH of a 0.01 M solution of a substance is 12.0, what does that tell you about the substance? I. It is an acid II. It is a base III. The substance is completely ionized IV. The substance is not completely ionized a. I and III b. II and III c. I and IV d. II and IV
b. II and III
What is the pH of a 0.50 M solution of HCl?
a. 0.30
b. 0.50
c. 7.0
d. 13.7
a. 0.30
When a bond between two atoms is broken:
a. Energy is released to the surroundings
b. Energy is absorbed from the surroundings
c. Energy is released or absorbed, depending on the system
d. The energy of the two atom system does not change because energy can neither be created nor destroyed
b. Energy is absorbed from the surroundings
What mass of Na2CO3 will completely react with 75 mL of 0.20 M HCl? Na2CO3 (aq) + 2 HCl (aq) -> 2 NaCl (aq) + H2CO3 (aq)
a. 0.20 g
b. 0.80 g
c. 1.6 g
d. 7.5 g
b. 0.80 g
When pure water is heated, the hydronium ion concentration increase. this means that.... I. The pH increases II. The pH decreases III. The water becomes acidic IV. The water becomes basic a. I only b. II only c. I and III d. I and IV e. II and III f. II and Iv
b. II only
What is the enthalpy change for the reaction shown below? C2H2 + 2H2 -> C2H6 a. -294 kJ/mole b. +295 kJ/mole c. -3712 kJ/mole d. +3712 kJ/mole
a. -294 kJ/mole
Given this information below for a reaction A + B -> products, which set of concentrations will allow you to determine the order of reaction with respect to [B]? [A] = 4; [B] = 4; Initial rate = 2 a. [A] = 2; [B] = 2 b. [A] = 4; [B] = 2 c. [A] = 2; [B] = 4 d. [A] = 1; [B] = 2
b. [A] = 4; [B] = 2
A reaction A -> B is monitored at constant temperature. You would predict that the rate of reaction at t = 20 s, relative to the rate at t = 0 s, is:
a. Slower, because there are fewer molecules bumping into each other
b. Slower, because the molecules have to get over the activation energy barrier
c. Faster, because the reaction has been given some energy to get over the activation energy barrier at the start
d. Faster, because the molecules gathered momentum
a. Slower, because there are fewer molecules bumping into each other
The rate equation for a reaction A + B -> product is: rate = k[A]^2[B]. What happens to the rate of the reaction if the concentration of A is doubled and the concentration of B is halved? The temperature is unchanged/
a. The rate halves
b. The rate doubles
c. The rate increases by four
d. The rate stays the same
b. The rate doubles
A catalyst…
I. Increases the amount of product at equilibrium
II. Shifts the equilibrium state toward the product side
III. Changes the route the reaction takes between reactants and products
a. I only
b. II only
c. III only
d. I and II
e. I and III
f. II and III
c. III only
Calculate the equilibrium constant K for the following equilibrium if the concentration of the various components at equilibrium are shown: 3 F2 (g) + Cl2 (g) -> 2 ClF3 (g) At equilibrium: [F2(g)] = 2.0 M [Cl2(g)] = 2.5 M [ClF3(g)] = 3.0 M a. 0.45 b. 0.60 c. 1.20 d. 1.80
a. 0.45
Which of the following statements is always true about any chemical reaction that is at equilibrium?
a. The molecules stop reacting
b. Only side reactions continue; the main reaction stops
c. The amounts of products and reactants are the same at equilibrium
d. The forward and reverse reactions occur at equal rates
d. The forward and reverse reactions occur at equal rates
What is the pH of a 0.30 M solution of hydrazoic acid, HN3? The Ka of hydrazoic acid is 1.9 x 10^-5?
a. 0.523
b. 1.22
c. 2.62
d. 4.72
c. 2.62
The activation energy for the formation of HI(g) from H2(g) and I2(g) is 170 kJ per mole of H2 or I2. The change in enthalpy for the reaction in the forward direction is +50 kJ. H2(g) + I2(g) -> 2 HI(g) ΔH = + 50 kJ What is the activation energy for the reverse reaction, that is, the decomposition of HI(g) into H2(g) and I2(g)? a. 25 kJ b. 50 kJ c. 120 kJ d. 170 kJ e. 220 kJ
c. 120 kJ
When the reaction A + B -> C + D is at equilibrium, addition of more C will cause the equilibrium position to shift to the left (to product more reactants). Why?
a. Because a stress has been applied to the equilibrium
b. Because the rate of the reverse reaction increases
c. Because of Le Chatelier’s principle
d. Because K decreases when product is added
b. Because the rate of the reverse reaction increases
A radioactive isotope decomposes via a first-order reaction. What is the half-life (in minutes) of the isotope if 75% of the isotope decomposed in 1.3 hours?
a. 3.1 min
b. 18 min
c. 28 min
d. 39 min
e. 78 min
f. 188 min
d. 38 min
Which of the following statements is/are true about a system at equilibrium? I. The value of ΔG ° tells you the free energy change if all substances are mixed at initial concentrations of 1.0 M at room temperature and atmospheric pressure II. At equilibrium ΔG ° is equal to zero III. At equilibrium ΔG is equal to zero a. I only b. II only c. II and III d. I and II e. I and III f. I, II, and III
e. I and III
Why does increasing the temperature affect the rate of a reaction?
I. The frequency of collisions increases, therefore increasing the probability of reaction
II. The energy of collisions increases, therefore more of the collisions transfer enough energy to get over the activation energy barrier
III. The activation energy barrier is lower, thus more reactant molecules have enough energy to get over the activation energy barrier
IV. ΔG becomes more negative, therefore making it more likely that more products will be produced
a. I
b. I and II
c. II and III
d. All of them
b I and II
For the reaction given below: K BrO-(aq) of HSCN(aq)
Identify the weaker Broasted-Lowry acid in the reaction
a. HBrO
b. SCN-
c. BrO-
d. HSCN
a. HBrO
Which one of the following substances is the weakest acid?
a. Uric acid, pKa = 3.9
b. Hydrocyanic acid, pKa = 9.2
c. Ascorbic acid, pKa = 4.1
d. Oxalic acid, pKa = 1.2
e. All of the listed acids are the same strength
b. Hydrocyanic acid, pKa = 9.2
