chem exam Flashcards by Sydney Drover

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

Emit energy from light, photons, creates line spectrum.

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

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

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

Orbital.

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

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

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MC: What is the basis of metallic bonding?

-Cations and delocalized electrons

Electrostatic attractions

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

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

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

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MC: What forces exist between ammonia particles?

Polar molecule so… LDF, HB, DD

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MC: What happens in an exothermic reaction?

Release of energy to the surroundings from the system.

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MC: What is an enthalpy change?

Difference!!! products - reactants

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MC: What is the law of conservation of energy?

Energy cannot be created or destroyed.

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

Activation energy.

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MC: Determine enthalpy change for a reaction.

Given synthesis, find 2x decomposition.

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MC: What are reaction mechanisms?

Elementary steps that make up an overall reaction.

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MC: What are ineffective collisions?

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

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

The rate constant.

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

Shift left, products decrease, reactants increase

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

Use Le Chatelier’s principle.

MC: What results when Keq increases?

Shift right, reactants decrease, products increase

MC: Determine the enthalpy and entropy of a reaction.

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

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

Weak acid and strong base.

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

Strong acid and weak base.

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

Shift log: 10^-pH

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

Shift away from OH- or towards H3O.

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

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

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

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

MC: What are the products of electrolysis of water?

2H2 and O2 (hydrogen and oxygen).

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

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

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

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

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

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

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

Whichever one has the highest charge -> probably HNO3.

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.

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

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

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

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

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

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

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

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 - ?

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

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

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

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?

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