Redox Reactions and Electrochemistry Quiz

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Questions and Answers

In the reaction MnO$_2$ + 4 HCl → MnCl$_2$ + Cl$_2$ + 2 H$_2$O, manganese is reduced and chlorine is oxidized.

True (A)

During the balancing of the half-reaction MnO$_4^−$ → Mn$_2$O$_3$ in acidic solution, water molecules must only be added to the reactant side.

False (B)

Electrolytic cells use an external power source to drive a spontaneous redox reaction.

False (B)

Increasing the temperature of a reaction will always decrease its rate.

<p>False (B)</p> Signup and view all the answers

A catalyst shifts the equilibrium of a reaction towards the products.

<p>False (B)</p> Signup and view all the answers

Adding a common ion to a saturated solution of a slightly soluble salt, such as NaCl, will increase the solubility of salt.

<p>False (B)</p> Signup and view all the answers

A strong acid will have a large Ka value and a small pKa value.

<p>True (A)</p> Signup and view all the answers

In the reaction 2Cr + 3Pb^{2+} \rightarrow 2Cr^{3+} + 3Pb, the standard cell potential, E^o, is -0.61 V.

<p>False (B)</p> Signup and view all the answers

A reaction with a standard cell potential, E^o, of -0.14V is considered to be spontaneous.

<p>False (B)</p> Signup and view all the answers

In the reaction 2H_2O + 2I^- \rightarrow 2OH^- + H_2 + I_2, the solution becomes less basic as the reaction proceeds.

<p>False (B)</p> Signup and view all the answers

In an electrolytic cell using a chromium anode and a cheap metal cathode for plating, chromium ions, Cr^{3+}, are reduced at the cathode.

<p>True (A)</p> Signup and view all the answers

The collision theory states that the rate of a reaction is determined only by the number of collisions between reactant molecules.

<p>False (B)</p> Signup and view all the answers

The rate determining step in a reaction mechanism is the fastest step in the reaction.

<p>False (B)</p> Signup and view all the answers

In the multi step reaction: 2A + B → AB + A, AB +C → ABC, ABC + C → AC_2 +B, and AC + AC → A_2C +C, 'A' acts as a catalyst.

<p>True (A)</p> Signup and view all the answers

For an exothermic reaction, the potential energy of the products is greater than the potential energy of the reactants.

<p>False (B)</p> Signup and view all the answers

The rate law gives information about the effect of pressure on reaction rate.

<p>False (B)</p> Signup and view all the answers

An increase in temperature typically decreases the reaction rate of a chemical process.

<p>False (B)</p> Signup and view all the answers

A catalyst alters the activation energy of a reaction, providing a pathway with a higher activation energy.

<p>False (B)</p> Signup and view all the answers

In the reaction $3A \rightarrow 5B$, if the rate of formation of B is 0.08 M/min then the rate of consumption of A is 0.048 M/min.

<p>True (A)</p> Signup and view all the answers

For a reaction that occurs in a single step, the rate law can always be determined solely from the stoichiometry of the reaction.

<p>True (A)</p> Signup and view all the answers

If a reaction is exothermic, the potential energy of the products is lower than the potential energy of the reactants.

<p>True (A)</p> Signup and view all the answers

The rate determining step of a reaction mechanism is the fastest step in the sequence.

<p>False (B)</p> Signup and view all the answers

An intermediate in a reaction is a stable product which can be isolated from the reaction mixture at the end of the reaction.

<p>False (B)</p> Signup and view all the answers

If the concentration of a reactant is doubled and the reaction rate quadruples this suggests that the reaction rate has a second order dependence on that reactant.

<p>True (A)</p> Signup and view all the answers

In a multi-step reaction mechanism, the sum of the steps must equal the overall reaction stoichiometry.

<p>True (A)</p> Signup and view all the answers

The rate constant for a reaction generally decreases with an increase in temperature.

<p>False (B)</p> Signup and view all the answers

In the reaction A + B C + D, with a Kc of 64, if 6.0 moles of each reactant are placed in a 4.0 L chamber, the equilibrium concentration of the products will be greater than 1.4 M.

<p>True (A)</p> Signup and view all the answers

The solubility of calcium sulfate, CaSO4, in a 0.15 M solution of MgSO4 is approximately 2.57 x 10^-4M.

<p>True (A)</p> Signup and view all the answers

If iron(II) iodide, FeI2, has a molar solubility of $7.3 x 10^{-9}$ M, then the concentration of Fe$^{2+}$ is $7.3 x 10^{-9}$ M and I$^-$ is $1.46 x 10^{-8}$ M, and the Ksp is about $7.43 x 10^{-24}$

<p>True (A)</p> Signup and view all the answers

For the reaction A + heat B, at equilibrium, if more of A than B is present, decreasing A will cause the system to shift towards the reactants to reach equilibrium again.

<p>False (B)</p> Signup and view all the answers

In the equilibrium reaction $P_4(g) + 6H_2(g) \leftrightarrow 4PH_3(g)$, adding more $H_2(g)$ will shift the equilibrium to the right, increasing the quantity of $PH_3(g)$ at equilibrium.

<p>True (A)</p> Signup and view all the answers

For a reaction with the rate law R = k[A]^1[B]^2, the reaction is first order with respect to A and second order with respect to B.

<p>True (A)</p> Signup and view all the answers

If the rate of formation of NH3 is 3.76 x 10^-4 M/s, then the rate of disappearance of H2 is 5.64 x 10^-4 M/s, based on the provided data.

<p>False (B)</p> Signup and view all the answers

Given the rate law R = k[NO]^2[Cl2]^1, and a rate constant k = 0.152 M^-2s^-1, the overall order of the reaction is 4.

<p>False (B)</p> Signup and view all the answers

Given the rate of a reaction with respect to A is expressed as Rate of A = 2/3 - ∆[B] / ∆t, this implies that 2 moles of A are consumed for every 3 moles of B consumed.

<p>False (B)</p> Signup and view all the answers

For the equilibrium 2SO3(g) ↔ 2SO2(g) + O2(g), with [SO3] = 0.0160 M, [SO2] = 0.00560 M, and [O2] = 0.00210 M, the equilibrium constant $K_c$ is calculated simply as $(0.00560 * 0.00210) / 0.0160$.

<p>False (B)</p> Signup and view all the answers

In the equilibrium N2(g) + 3H2(g) ↔ 2NH3(g) + 92 kJ, increasing the temperature will shift the equilibrium towards the reactants.

<p>True (A)</p> Signup and view all the answers

In the reaction H2(g) + CO2(g) ↔ H2O(g) + CO(g), adding H2(g) would cause the equilibrium to shift to the left.

<p>False (B)</p> Signup and view all the answers

For the reaction 4 NH3(g) + 5 O2(g) ↔ 4 NO(g) + 6 H2O(g) with $K_c= 5.0 x 10^{-19}$, the concentrations at equilibrium will predominantly favor the products.

<p>False (B)</p> Signup and view all the answers

If 6.0 mol of CO and 6.0 mol of H2O are placed in a 2.0 L container, with the reaction CO(g) + H2O(g) ↔ H2(g) + CO2(g), and Kc = 0.80, the equilibrium concentration of H2 will always be less than the equilibrium concentration of CO.

<p>False (B)</p> Signup and view all the answers

For a reaction where $K_c$ = 3.63, with the concentrations of reactants and products provided, if the calculated Reaction Quotient Q is greater than $K_c$, the reaction shifts towards the reactants to reach equilibrium.

<p>True (A)</p> Signup and view all the answers

Flashcards

Oxidation

The process where an atom, ion or molecule loses electrons and increases its oxidation number.

Reduction

The process where an atom, ion or molecule gains electrons and decreases its oxidation number.

Oxidizing Agent

A substance that causes another substance to be oxidized, while being reduced itself.

Reducing Agent

A substance that causes another substance to be reduced, while being oxidized itself.

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Balancing Redox Reactions

The process of balancing chemical equations by separating them into half-reactions that represent oxidation and reduction.

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Electrolytic Cell

An electrochemical cell that uses an external electrical current to drive a non-spontaneous chemical reaction.

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Electroplating

The process of coating a metal object with a thin layer of another metal using electrolysis.

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Collision Theory

The collision theory states that for a chemical reaction to occur, reactant molecules must collide with sufficient energy and proper orientation. This collision must overcome the activation energy barrier for the reaction to proceed.

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Factors affecting Reaction Rate

Factors that affect the rate of reaction include: temperature, concentration, surface area, catalyst presence, and the nature of the reactants. Increasing temperature, concentration, or surface area generally increases the rate. Catalysts speed up reactions, while the nature of reactants dictates their inherent reactivity.

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Reaction Mechanism

A reaction mechanism is a step-by-step description of how a chemical reaction occurs. It breaks down the overall reaction into a series of elementary steps, each involving a collision between molecules.

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Rate Determining Step

The rate determining step (RDS) is the slowest step in a reaction mechanism. This step controls the overall rate of the reaction. It's like the bottleneck in a production line, limiting how fast the product can be made.

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Potential Energy Diagram

Potential energy diagrams show the energy changes during a chemical reaction. Reactants start at a certain energy level, and progress through a transition state (activated complex) before reaching products at a different energy level. The activation energy is the minimum energy required for the reaction to occur.

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Reaction Rate

Reaction rate is the change in concentration of a reactant or product over time. It can be expressed as a differential equation or as the slope of a tangent line on a concentration vs. time graph.

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Rate Law

The rate law for a chemical reaction relates the rate of the reaction to the concentrations of the reactants. It tells you how the rate of change depends on the concentration of each reactant. For example, a rate law of Rate = k[A]^2[B] indicates that the rate is directly proportional to the square of the concentration of reactant A and the concentration of reactant B.

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Catalyst

A catalyst is a substance that speeds up the rate of a chemical reaction without itself being permanently consumed. It does this by providing an alternative reaction pathway with lower activation energy enabling more molecules to collide effectively.

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Intermediate

An intermediate is a species that is formed and consumed during the course of a reaction mechanism. Unlike catalysts, intermediates are not present at the start or end of the overall reaction. They are like temporary helpers in a multi-step process.

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Solubility Product Constant (Ksp)

The solubility product constant (Ksp) represents the product of the ion concentrations raised to their stoichiometric coefficients in a saturated solution of a sparingly soluble salt.

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Molar Solubility

Molar solubility refers to the number of moles of a solute that dissolve in one liter of a saturated solution.

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Reaction Quotient (Q)

The reaction quotient (Q) is a measure of the relative amounts of products and reactants present in a reaction at any given time.

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Concentration vs. Time Graph

The change in concentration of a substance as a function of time. It can be used to describe both the rate of formation of products and the depletion of reactants in a chemical reaction.

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Le Chatelier's Principle

A change in the conditions of a reaction at equilibrium can shift the equilibrium position to favour either the forward or reverse reaction.

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Effective Collisions

The rate of a reaction depends on the number of collisions per unit time and the effectiveness of these collisions. Only effective collisions lead to product formation.

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Activation Energy and Orientation

For a collision to be effective, the reacting particles must possess sufficient energy (activation energy) and have the correct orientation to break existing bonds and form new ones.

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Rate Law Expression

The rate law expression for a reaction describes how the rate of the reaction depends on the concentrations of the reactants.

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Rate Law for a Single-Step Reaction

For a single-step reaction, the rate law expression can be directly determined from the stoichiometry of the balanced chemical equation.

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Rate Constant (k)

The rate constant (k) is a proportionality constant in the rate law equation. It reflects the reaction's inherent speed at a given temperature.

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Determining Rate Law and Rate Constant

The rate law and rate constant can be determined experimentally by analyzing how the reaction rate changes with different initial concentrations of reactants.

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Rate of Reaction

A measure of how fast a reaction proceeds. It is the change in the concentration of a reactant or product over a specific time interval.

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Differential Rate Law

A mathematical equation that describes how the rate of a chemical reaction depends on the concentrations of the reactants. It defines the relationship between the rate of disappearance of reactants and the rate of appearance of products.

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Equilibrium

A state where the forward and reverse reaction rates are equal, leading to no net change in the amounts of reactants and products. The system reaches a balance between formation of products and conversion back to reactants.

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Kc (Equilibrium Constant in terms of concentration)

The equilibrium constant for a reaction involving aqueous solutions. It represents the ratio of the product of the concentrations of products to the product of the concentrations of reactants, each raised to the power of their stoichiometric coefficient in the balanced equation.

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Kp (Equilibrium Constant in terms of pressure)

The equilibrium constant for a reaction involving gases. It represents the ratio of the product of the partial pressures of products to the product of the partial pressures of reactants, each raised to the power of their stoichiometric coefficient in the balanced equation.

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Rate of Change in Concentration

The change in the amount of a substance in a reaction over a period of time. It's typically expressed as moles per liter per second (M/s) or as a change in concentration over time. It describes how the concentration of a reactant or product changes as the reaction progresses.

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Vapor Pressure

The tendency for a liquid to evaporate. It's higher for substances with weaker intermolecular forces and lower for substances with stronger intermolecular forces.

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Ksp (Solubility Product)

The equilibrium constant for the dissolution of a sparingly soluble ionic compound. It represents the product of the concentrations of the constituent ions, each raised to the power of their stoichiometric coefficient in the balanced dissolution equation. A larger Ksp means higher solubility.

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Study Notes

Chemistry 40S Exam Review

  • This review package provides examples of long-answer questions covering the units studied. It does not include all theory; students should also use their notes and unit booklets. Tests and quizzes are also recommended for preparation.
  • Topics Covered: Oxidation-Reduction and Electrochemistry, Chemical Kinetics, Chemical Equilibrium and Ksp, Acids and Bases, and Atomic Structure.

Oxidation-Reduction and Electrochemistry

  • Includes oxidation numbers, oxidizing/reducing agents, balancing redox reactions (acidic/basic solutions), electrolytic cells, electroplating, electrochemical cells, and corrosion.

Chemical Kinetics

  • Covers reaction rates, factors affecting rates (collision theory), reaction mechanisms, and rate laws (reaction orders). Includes catalyzed and uncatalyzed reactions and mechanisms.

Chemical Equilibrium and Ksp

  • Includes mass action expressions, equilibrium constants (kc and kp), percent yield of product, ICE charts, Le Chatelier's principle, interpretations of graphs, and calculation of solubility products (ksp) and molar solubilities.

Acids and Bases

  • Compares electrolytes and nonelectrolytes, Arrhenius and Brønsted-Lowry definitions, conjugate acid-base pairs, self-ionization of water (Kw), ionization constants (Ka and Kb), pH/pOH scales, calculations, and titration procedures.

Atomic Structure

  • Includes the quantum mechanical model of the atom, electron configurations, orbital diagrams, calculations for wavelength, frequency, and energy, types of spectra (continuous, bright line), and periodic trends (atomic/ionic radii, ionization energy, electronegativity).

Electrochemistry Answers (Additional Information)

  • Balancing Redox Equations: Shows examples, including half-reaction method and oxidation number method, for balancing chemical equations involving oxidation and reduction.
  • Electrochemical Cells: Includes balanced equations, electrochemical cell diagrams, anode/cathode identification, electron flow directions, and calculation of the voltage (E°).
  • Spontaneity Prediction: Explains how to determine if a reaction will occur spontaneously and writes out the products of a reaction given the reactants.
  • Electrolysis: Given aqueous Nal electrolysis, equations for oxidation and reduction are written. The minimum voltage necessary for the reaction to proceed, and pH changes during the electrolysis process are evaluated.
  • Electrolytic Cells and Electroplating: Covers how to construct an electrolytic cell for electroplating, gives the two half-reactions involved and labels the anode, cathode, and electrolyte.

Kinetics (Additional Information)

  • Reaction Rates: Includes the factors affecting the rate of a chemical reaction, collision theory, and effective collisions.
  • Reaction Mechanisms: Covers reaction mechanisms, rate-determining steps, derivation of possible reaction mechanisms, identification of catalysts and intermediates.
  • Potential Energy Graphs: Explains how to draw potential energy diagrams for exothermic reactions, show reactants, products, activated complex, activation energies, and heats of reaction on the graphs, and identify these features when a catalyst is included,
  • Calculation of Reaction Rates: Shows how to find the rate of reaction given concentration changes over time, using the example of the consumption of reactants and the formation of products for N2 + 3H2 → 2NH3
  • Rate Laws: Includes the relationship of reaction rate to concentrations of reactants and the rate constant.

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