chem exam

Question 1

MC: What is produced when electrons return to lower energy levels?

Answer 1

Emit energy from light, photons, creates line spectrum.

Question 2

MC: What was Planck’s contribution to the quantum mechanical model?

Answer 2

• Energy emitted/absorbed
• Units (quanta) and packets (quantum).
• Experimental results from hot objects emitting light.

Question 3

MC: A region of space where there is a high probability of electrons?

Answer 3

Orbital.

Question 4

MC: Which of the following is the electron configuration for a halogen?

Answer 4

Group 17, valence electrons: s^2, p^5

Question 5

MC: What is the basis of metallic bonding?

Answer 5

-Cations and delocalized electrons

• Electrostatic attractions

-Atomic strength of the bond depends on the nuclear charge and #e- in the outer orbital

Question 6

MC: Which of the following substances would NOT be polar?

Answer 6

Weakest intermolecular forces, or dipoles cancel. EX- CH4.

Question 7

MC: What forces exist between ammonia particles?

Answer 7

Polar molecule so… LDF, HB, DD

Question 8

MC: What happens in an exothermic reaction?

Answer 8

Release of energy to the surroundings from the system.

Question 9

MC: What is an enthalpy change?

Answer 9

Difference!!! products - reactants

Question 10

MC: What is the law of conservation of energy?

Answer 10

Energy cannot be created or destroyed.

Question 11

MC: What is the amount of energy required for a reaction to begin?

Answer 11

Activation energy.

Question 12

MC: Determine enthalpy change for a reaction.

Answer 12

Given synthesis, find 2x decomposition.

Question 13

MC: What are reaction mechanisms?

Answer 13

Elementary steps that make up an overall reaction.

Question 14

MC: What are ineffective collisions?

Answer 14

Wrong orientation, not enough energy and come apart, do not proceed to products

Question 15

MC: What is the rate of the reaction proportional to?

Answer 15

The rate constant.

Question 16

MC: What happens to the equilibrium system if Keq decreases?

Answer 16

Shift left, products decrease, reactants increase

Question 17

MC: Which of the following would result in the increase of hydrogen gas?

Answer 17

Use Le Chatelier’s principle.

Question 18

MC: What results when Keq increases?

Answer 18

Shift right, reactants decrease, products increase

Question 19

MC: Determine the enthalpy and entropy of a reaction.

Answer 19

Enthalpy: Energy. Look to which side KJ is on.
Entropy: Disorder. Look to states.

Question 19

MC: Which of the following salts acts like a base when it is in water?

Answer 19

Weak acid and strong base.

Question 20

MC: Which of the following salts acts like an acid when it is in water?

Answer 20

Strong acid and weak base.

Question 21

MC: Calculate the molar concentration pH of a solution of perchloric acid.

Answer 21

Shift log: 10^-pH

Question 22

MC: What happens when a base is added to the buffer system?

Answer 22

Shift away from OH- or towards H3O.

Question 23

MC: Identify the oxidizing agent and reducing agent in a chemical reaction.

Answer 23

OA: reactant that is reduced
RA: reactant that is oxidized

Question 24

MC: What is the oxidation number of chromium in the following ion?

Answer 24

Figure out charge. Ex: Cr2O3 ->Cr would be +3.

Question 25

MC: What are the products of electrolysis of water?

Answer 25

2H2 and O2 (hydrogen and oxygen).

Question 26

MC: What is the function of a salt bridge in a galvanic cell?

Answer 26

Allow the passage of ions, and maintain electrical neutrality of the two solutions.

Question 27

MC: Which of the following statements about electrolytic cells is false?

Answer 27

Examples of false statements:
- reduction at anode
- cathode is depleted
- e- flow from pos terminal

Question 28

MC: Moles of electrons required to produce two moles of Cadmium?

Answer 28

Look to OA/RA sheet» 4 moles of e-. (2 needed for only 1)

Question 29

MC: In which compound does nitrogen have the highest oxidation number?

Answer 29

Whichever one has the highest charge -> probably HNO3.

Question 30

SHORT ANSWER: Write out the electron configuration for any nonmetal, state # of valence electrons and the noble gas it will be isoelectronic with as an ion.

Answer 30

Oxygen. 1s^2 2s^2 2p^4
6 Valence electrons.
O^2-. 1s^2 2s^2 2p^6
Isoelectronic with neon.

Question 31

SHORT ANSWER: Explain why ammonia has a high solubility in water.

Answer 31

• Readily forms hydrogen bonds, and dissolves in water
• Nitrogen has a lone pair of electrons, which will also contribute (Polarity)

Question 32

SHORT ANSWER: List the 4 methods used to communicate a change in enthalpy.

Answer 32

1) Molar enthalpy
2) Enthalpy change
3) Term in the equation
4) Potential energy diagram

Question 33

SHORT ANSWER: What are the two requirements for a plausible reaction mechanism?

Answer 33

1) The sum of the mechanism steps matches the observed reaction.
2) The mechanism accounts for the experimentally observed rate law.

Question 34

SHORT ANSWER: Explain the reason why the reaction will shift when various reagents are added to the following eq system;
2 CrO4 2(aq) + 2 H (aq) <==> Cr207(aq) + H20(l)
NaOH added - ?
HCl added - ?
KCl added - ?
Ba2+ added - ?

Answer 34

NaOH added - shift left - OH ions pull protons out of solution
HCl added - right - added more H shift away
KCl added - no shift - no common ion
Ba2+ added - shift left - precipitate form - Barium ions pull out of CrO 2- 4

Question 35

SHORT ANSWER: Determine the pH when a specific salt is added to water. LiBr, ZnI2, MgCN2

Answer 35

Strong acid + Strong base = Neutral salt (pH=7) LiBr
Strong acid + Weak base = Acidic salt (pH>7) ZnI2
Weak acid + Strong base = Basic salt (pH<7). MgCN2

Question 36

SHORT ANSWER: Explain why an oxidation-reduction reaction occurs and does not occur. What important rule is followed in determining if a reaction is spontaneous?

Answer 36

• OA>RA - spontaneous - occurs
• RA> OA - non-spontaneous - does not occur
• Redox spontaneity rule!