Reactions & Stoichiometry – CHEF 0314 (Topic 1a)

Question-and-answer flashcards covering balancing equations, reaction types, solubility, acids and bases, redox concepts, oxidation numbers, and balancing redox reactions.

In a chemical equation, on which side are the reactants written?

On the left side of the arrow.

What are the products in a chemical equation?

The substances written on the right side of the arrow that are formed in the reaction.

Give the balanced molecular equation for the complete combustion of octane (C8H18).

2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(g).

Which two general methods can be used to balance chemical equations?

Inspection (trial-and-error) and algebraic (using variables for coefficients).

Write the balanced equation for the combustion of methane (CH4).

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g).

What is the molecular equation for the reaction between KO2 and CO2 in a breathing apparatus?

4 KO2(s) + 2 CO2(g) → 2 K2CO3(s) + 3 O2(g).

What does a molecular equation show?

All reactants and products as intact, undissociated compounds.

What is a total ionic equation?

An equation that shows all soluble ionic substances dissociated into their constituent ions.

Define net ionic equation.

An equation that eliminates spectator ions and shows only the species that actually change during the reaction.

Name the three common types of aqueous reactions discussed.

Precipitation reactions, acid-base (neutralization) reactions, and redox reactions.

List the three steps for predicting whether a precipitate will form.

1) Note the ions present, 2) consider possible cation–anion combinations, 3) decide if any combination is insoluble.

According to the solubility rules, all compounds of Group 1A ions and NH4+ are…

Soluble in water.

Which chloride salts are insoluble?

Chlorides of Ag+, Pb2+, Hg22+, and Cu+.

Are sulfates of Ba2+ soluble or insoluble?

Insoluble (BaSO4 is insoluble).

Write the net ionic equation for mixing NaF(aq) and CaCl2(aq).

Ca2+(aq) + 2 F−(aq) → CaF2(s).

Identify the spectator ions when NaI(aq) reacts with Pb(NO3)2(aq).

Na+ and NO3−.

State the Arrhenius definition of an acid.

A substance that increases the concentration of H+(aq) when dissolved in water.

State the Arrhenius definition of a base.

A substance that increases the concentration of OH−(aq) when dissolved in water.

According to Brønsted–Lowry theory, what is an acid?

A proton (H+) donor.

Give an example of a strong acid and a weak acid from the lecture.

Strong: HCl; Weak: CH3COOH (acetic acid).

Name two strong bases listed in the notes.

NaOH and KOH (others include Ca(OH)2, Sr(OH)2, Ba(OH)2).

What is the net ionic equation for neutralizing Sr(OH)2 with HClO4?

2 OH−(aq) + 2 H+(aq) → 2 H2O(l).

Define oxidation in terms of electrons.

Loss of electrons (increase in oxidation number).

Define reduction in terms of electrons.

Gain of electrons (decrease in oxidation number).

In the reaction Zn(s) + 2 H+(aq) → Zn2+(aq) + H2(g), which species is the reducing agent?

Zn(s), because it loses electrons (is oxidized).

Give the oxidation-number rule for any free (elemental) atom.

The oxidation number of an element in its elemental form is 0.

What is the oxidation number of hydrogen when bonded to metals?

−1.

State the oxidation number of oxygen in peroxides.

−1 (instead of the usual −2).

Is the reaction CaO + CO2 → CaCO3 a redox reaction?

No, because no oxidation numbers change.

What are the two half-reactions in the acidic-medium redox example Cr2O72− + I− → Cr3+ + I2?

Reduction: Cr2O72− + 14 H+ + 6 e− → 2 Cr3+ + 7 H2O; Oxidation: 2 I− → I2 + 2 e−.

List the main steps in the half-reaction method for balancing redox equations.

1) Split into half-reactions; 2) Balance atoms (except O, H), 3) Balance O with H2O, 4) Balance H with H+, 5) Balance charge with e−, 6) Equalize electrons, 7) Add half-reactions and simplify.

How do you adjust an acidic half-reaction to basic conditions?

Add the same number of OH− ions to both sides to neutralize H+ and combine to form H2O, then cancel waters as needed.

Provide the balanced basic-medium equation for Cr2O72− + I−.

Cr2O72− + 6 I− + 14 OH− → 2 Cr3+ + 3 I2 + 7 H2O.

Write the balanced redox equation (basic medium) for MnO4− and C2O42− given: 2 MnO4− + 3 C2O42− + 4 OH− → 2 MnO2 + 6 CO32− + 2 H2O. What species is oxidized?

C2O42− is oxidized to CO32− (carbon oxidation number increases from +3 to +4).

For monoatomic ions, how is the oxidation number determined?

It equals the ion’s charge.

What defines an oxidizing agent?

A species that is reduced (gains electrons) and causes oxidation of another substance.

What defines a reducing agent?

A species that is oxidized (loses electrons) and causes reduction of another substance.