Chapter 11

What is a free element, and what is the oxidation number for atoms that exist as a free element?

What is the highest oxidation number that sulfur can have? The lowest? Consider the number of valence electrons it has.

Determine the oxidation numbers of each of the atoms in the following. a. \(\mathrm{KMnO}_{4}\) b. \(\mathrm{OCl}_{2}\) c. \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) d. \(\mathrm{Li}_{3} \mathrm{PO}_{4}\) e. \(\mathrm{NaClO}\) f. \(\mathrm{Br}_{2}\) g. \(\mathrm{ClF}_{3}\) h. \(\mathrm{CaCl}_{2}\) i. \(\mathrm{K}_{2} \mathrm{O}\)

Determine the oxidation number of each of the atoms in the following ions. a. \(\mathrm{NO}_{2}^{-}\) b. \(\mathrm{NO}_{3}^{-}\) c. \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\) d. \(\mathrm{BrO}_{3}^{-}\) e. \(\mathrm{ClO}_{3}\) f. \(\mathrm{BO}_{3}{\underline{\phantom{xx}}}^{3-}\) g. \(\mathrm{CO}_{3}{\underline{\phantom{xx}}}^{2-}\) h. \(\mathrm{NH}_{4}^{+}\) i. \(\mathrm{CrO}_{4}^{2-}\) j. \(\mathrm{S}_{2} \mathrm{O}_{3}^{2-}\)

Explain why oxidation and reduction always occur together in a reaction.

What happens to the oxidizing agent in a redox reaction?

What happens to the reducing agent in a redox reaction?

Identify each process as an oxidation or a reduction. a. \(\mathrm{Rb} \rightarrow \mathrm{Rb}^{+}\) b. \(\mathrm{Te} \rightarrow \mathrm{Te}^{2-}\) c. \(2 \mathrm{H}^{+} \rightarrow \mathrm{H}_{2}\) d. \(\mathrm{P}^{3-} \rightarrow \mathrm{P}\) e. \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}\) f. \(\mathrm{Sn}^{4+} \rightarrow \mathrm{Sn}^{2+}\) g. \(\mathrm{Br}_{2} \rightarrow \mathrm{Br}^{-}\) h. \(\mathrm{Fe}^{2+} \rightarrow \mathrm{Fe}^{3+}\)

For each equation, 1 ) identify the oxidation numbers of each element, 2) determine if it is a redox reaction or not, and for redox reactions, 3) identify the species being oxidized and the species being reduced, and 4) identify the oxidizing and reducing agents. a. \(2 \mathrm{KClO}_{3}(s) \rightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g)\) b. \(\mathrm{H}_{2}(g)+\mathrm{CuO}(s) \rightarrow \mathrm{Cu}(s)+\mathrm{H}_{2} \mathrm{O}(l)\) c. \(2 \mathrm{Al}(s)+3 \operatorname{Sn}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow 2 \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}(a q)+3 \mathrm{Sn}(s)\) d. \(2 \mathrm{HNO}_{3}(a q)+6 \mathrm{HI}(a q) \rightarrow 2 \mathrm{NO}(g)+3 \mathrm{I}_{2}(s)+4 \mathrm{H}_{2} \mathrm{O}(l)\) e. \(\mathrm{AgNO}_{3}(a q)+\mathrm{NaCl}(a q) \rightarrow \mathrm{AgCl}(s)+\mathrm{NaNO}_{3}(a q)\) f. \(2 \mathrm{FeCl}_{3}(a q)+\mathrm{H}_{2} \mathrm{~S}(g) \rightarrow 2 \mathrm{FeCl}_{2}(a q)+2 \mathrm{HCl}(a q)+\mathrm{S}(s)\)

Classify the following reactions as combination, decomposition, single replacement, double replacement, or combustion. For each, indicate if it is a redox reaction or not. a. \(\mathrm{Cd}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CdSO}_{4}(a q)+\mathrm{H}_{2}(g)\) b. \(2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s)\) ?. \(\mathrm{C}_{7} \mathrm{H}_{8}(l)+9 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 7 \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(g)\) d. \(2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \rightarrow 2 \mathrm{~N}_{2}(g)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)\) e. \(2 \mathrm{CoCl}_{3}(a q)+3 \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow 2 \mathrm{Co}\left(\mathrm{NO}_{3}\right)_{3}(a q)+3 \mathrm{PbCl}_{2}(s)\)

Balance the following equations and classify the following reactions as combination, decomposition, single replacement, double replacement, or combustion. For each, indicate if it is a redox reaction or not. a. \(\mathrm{Na}+\mathrm{Cl}_{2} \rightarrow \mathrm{NaCl}\) b. \(\mathrm{Na}_{3} \mathrm{PO}_{4}+\mathrm{KOH} \rightarrow \mathrm{NaOH}+\mathrm{K}_{3} \mathrm{PO}_{4}\) c. \(\mathrm{P}_{4}+\mathrm{O}_{2} \rightarrow \mathrm{P}_{2} \mathrm{O}_{3}\) d. \(\mathrm{N}_{2}+\mathrm{H}_{2} \rightarrow \mathrm{NH}_{3}\) e. \(\mathrm{Al}+\mathrm{HCl} \rightarrow \mathrm{H}_{2}+\mathrm{AlCl}_{3}\) f. \(\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\) g. \(\mathrm{NH}_{3}+\mathrm{CuO} \rightarrow \mathrm{Cu}+\mathrm{N}_{2}+\mathrm{H}_{2} \mathrm{O}\) h. \(\mathrm{NH}_{4} \mathrm{NO}_{3} \rightarrow \mathrm{N}_{2} \mathrm{O}+\mathrm{H}_{2} \mathrm{O}\)

What do the products of combustion reactions have in common?

Write and balance combustion reactions for the following compounds. a. methane \(\left(\mathrm{CH}_{4}\right)\) b. propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) c. octane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\) d. ethanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right)\) e. sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\)

In a certain reaction, the energy of the reactants is less than the energy of the products (reaction consumes energy). Is the reaction endothermic or exothermic?

What are the two driving forces for all chemical reactions and physical processes?

How does an increase in temperature affect the entropy of a system?

Which system has the greater entropy in each of the following? a. solid sodium chloride or a sodium chloride solution b. bromine liquid or bromine vapor c. 25 g of water at \(80^{\circ} \mathrm{C}\) or 25 g of water at \(50^{\circ} \mathrm{C}\) d. liquid mercury or solid mercury

How does the entropy of a system change for each of the following processes? a. A solid melts. b. A liquid freezes. c. A liquid boils. d. A vapor condenses to a liquid. e. Sugar dissolves in water. f. A solid sublimes.

Can a proposed reaction be spontaneous and yet still not be observed to occur? Explain.

The forward reaction is spontaneous for a particular reversible reaction. What can you conclude about the spontaneity of the reverse reaction?

Explain how free energy is used to determine whether or not a reaction is spontaneous.

Under what conditions of enthalpy and entropy change is a reaction always spontaneous? Under what conditions is a reaction never spontaneous?

If the enthalpy change is unfavorable (endothermic), but the entropy change is favorable (increasing), would a high temperature or a low temperature be more likely to lead to a spontaneous reaction?

If the enthalpy change is favorable and the entropy change is favorable, would the reaction be spontaneous at high temperatures, low temperatures, or all temperatures?

In what unit is the rate of a chemical reaction typically expressed?

A \(2.50 \mathrm{M}\) solution undergoes a chemical reaction. After \(3.00\) minutes, the concentration of the solution is \(2.15 \mathrm{M}\). What is the rate of the reaction in \(\mathrm{M} / \mathrm{s}\) ?

Substance A disappears at a rate of \(0.0250 \mathrm{M} / \mathrm{s}\). If the initial concentration is \(4.00 \mathrm{M}\), what is the concentration after one minute?

The concentration of product B increases from 0 to \(1.75 \mathrm{M}\) in 45 seconds. What is the rate of formation of \(\mathrm{B}\) ?

The concentration of product B increases from \(0.50 \mathrm{M}\) to \(1.25 \mathrm{M}\) in \(2.5\) seconds. What is the rate of formation of \(\mathrm{B}\) ?

Reactant B goes from \(2.25 \mathrm{M}\) to \(1.50 \mathrm{M}\) in \(0.85\) seconds. What is the rate of change of \(\mathrm{B}\) ?

Does every collision between reacting particles lead to the formation of products? Explain.

Explain why the activation energy of a reaction is sometimes referred to as a barrier.

Why is it difficult to study activated complexes?

Explain how reaction rates can be affected by a. changes in concentration. b. changes in pressure. c. increased surface area. d. changes in temperatures.

What is the effect of a catalyst on the rate of a reaction?

Explain how the presence of a catalyst affects the activation energy of a reaction.

Zinc metal reacts with hydrochloric acid. Which one would result in the highest rate of reaction? a. A solid piece of zinc in \(1 \mathrm{M} \mathrm{HCl}\) b. A solid piece of zinc in \(3 \mathrm{M} \mathrm{HCl}\) c. Zinc powder in \(1 \mathrm{M} \mathrm{HCl}\) d. Zinc powder in \(3 \mathrm{M} \mathrm{HCl}\)