CHEM 1411 - Ch 10 Part B

Given the information below, calculate the lattice energy of KCl. K (s) → K (g); ΔH = 79.87 kJ/mol 1212Cl2 (g) → Cl (g); ΔH = 121.7 kJ/mol K (g) → K+ (g) + e-; ΔH = 418.8 kJ/mol Cl(g) + e-→ Cl-(g); ΔH = -349 kJ/mol ΔHf KCl = -435.87 kJ/mol

+707 kJ

Calculate the lattice energy of NaF using the data given. The lattice energy equation is NaF(s) → Na+(g) + F-(g). IE1(Na) = 496 kJ/mol EA1(F) = 328 kJ/mol ΔHfo[Na(g)] = 107.7 kJ/mol ΔHfo[F(g)] = 80.0 kJ/mol ΔHfo[NaF(g)] = -569.0 kJ/mol

+925 kJ

Calculate the standard enthalpy change for the reaction SiO2 (s) + 4HF (g) → SiF4 (g) + 2H2O (l) given the information in the table below.

-183.6 kJ

Select all of the statements that correctly describe bond enthalpies.

-Bond enthalpies are always positive. -Bond enthalpies represent the energy required to break bonds.

Using Hess's law, select the manipulation to the given formation equations necessary to generate the overall chemical equation for the combustion of diamond to carbon dioxide (an expensive experiment). Select all that apply, including the correct overall equation. We are given the following formation equations Eqn 1: C(graphite) + O2(g) → CO2(g) ΔH1 = -393.5 kJ Eqn 2: C(graphite) → C(diamond) ΔH2 = 1.88 kJ

-C(diamond) → C(graphite) ΔH2' = (-1)ΔH2 = -1.88 kJ -Overall equation is C(diamond) + O2(g) → CO2(g) ΔHrxn = -395.4 kJ

Ionic compounds differ significantly from molecular compounds. Select the all of the features that are typical of ionic compounds.

-Ionic substances tend to be solids at room temperature. -Ionic compounds have high melting points. -Ionic substances form electrically conductive solutions when dissolved.

Select the statements that correctly describe lattice energy.

-Lattice energy is a measure of the total strength of interaction between ions in the solid. -Lattice energy is the energy required to separate 1 mol of an ionic solid into gaseous ions.

Using Hess's law, select the manipulations to the given steps necessary to generate the overall chemical equation for the combustion of diamond to carbon monoxide (a difficult and expensive experiment). Select all that apply, including the correct overall equation. We are given the following thermochemical equations Eqn 1: C(graphite) + O2(g) → CO2(g) ΔH1 = -393.5 kJ Eqn 2: 2CO(g) + O2 (g) → 2CO2(g) ΔH2 = -566.0 kJ Eqn 3: C(diamond) → C(graphite) ΔH3 = -1.88 kJ

-Overall equation is 2C(diamond) + O2(g) → 2CO(g) ΔHrxn = -224.8 kJ -2CO2(g) → 2CO(g) + O2(g) ΔH2' = -ΔH2 = +566.0 kJ -2C(graphite) + 2O2(g) → 2CO2(g) ΔH1' = 2ΔH1 = -(2)393.5 kJ = -787.0 kJ -2C(diamond) → 2C(graphite) ΔH3' = 2ΔH3 = -(2)1.88 kJ = -3.76 kJ

CO (g) can be produced by the reaction of coal with steam, as shown by the balanced equation: H2O (g) + C (s) → CO (g) + H2 (g). Which of the following options correctly reflect the steps required to calculate ΔH for this reaction, given the information shown below? Select all that apply. Reaction 1: H2 (g) + 1212O2 (g) → H2O (g); ΔH = -242.0 kJ Reaction 2: 2CO (g) → 2C (s) + O2 (g); ΔH = +221.0 kJ

-Reaction 2 must be reversed and divided by 2. -ΔH = +131.5 kJ

Which of the following relationships are correct regarding forces of attraction in molecular and ionic species?

-The attractive forces between ions tend to be stronger than the attractive forces between adjacent molecules. -Weak forces between molecules result in gaseous, liquid, or low-melting covalent compounds.

Which of the following options correctly describe the procedure used to calculate ΔH for a reaction using bond energies? Select all that apply.

-ΔH for the reaction is given by (sum of ΔHbonds formed) + (sum of ΔHbonds broken) -The sum ΔHbonds broken is given a positive value.

Match the effects of the following combinations of Reactions 1 and 2 with the reaction resulting from these combinations. Reaction 1: A → 2C Reaction 2: C → B 1. Rxn 1 + (-Rxn 2) 2. Rxn 1 + 2(Rxn 2) 3. (-Rxn1) + (-Rxn 2)

1. A + B → 3C 2. A → 2B 3. B + C → A

Match each thermodynamic symbol with its correct definition. Instructions 1. ΔHrxn 2. ΔH°rxn 3. ΔH°f

1. The change in enthalpy for a given reaction 2. The enthalpy change of a reaction measured at the standard state 3. The enthalpy change when 1 mol of a compound forms from its elements in their standard states

Which of the following reactions is associated with the standard enthalpy of formation of NH3 (g)?

1/2 N2 (g) + 3/2 H2 (g) → NH3 (g)

Calculate ΔH°rxn for the reaction A + 2B → 2C using the ΔH°f values given below.

2(c) - (a) - 2(b)

Consider the following reactions: 2A → B; ΔH = x 2B → C; ΔH = y What is the total enthalpy change for the reaction 4A → C?

2x + y

To generate the overall equation A → 2C, which two equations should be added together?

A → B B → 2C

Two equations must be manipulated in order to generate the overall equation Br2 + 2NO → 2NOBr. Select the two chemical equations from below that can be arranged and added together to generate the overall equation. (Note: the equation(s) may need to be reversed or multiplied by a constant.)

Br2 + NO → NOBr2 2NOBr → NOBr2 + NO

Which of the following reactions would have an enthalpy change equal to ΔHf°? Select all that apply.

C(graphite) + O2 (g) → CO2 (g) Fe (s) + 3232Cl2 (g) → FeCl3 (s)

What is the net equation when the following reactions are summed? 2C(graphite) + 3H2 (g) → C2H6 (g) C2H4 (g) → 2C(graphite) + 2H2 (g)

C2H4 (g) + H2 (g) → C2H6 (g)

The formation of an ionic bond involves a number of different processes. If we consider the separate electron transfer processes involved in the formation of sodium chloride, which individual steps would require an input of energy? The overall process is represented by the equation shown below. Select all that apply. 2Na (s) + Cl2 (g) → 2NaCl (s)

Dissociation of Cl2 to form 2Cl Removal of an electron from Na Conversion of Na (s) → Na (g)

For a reaction that proceeds through a series of steps, ΔHoverall = ΔH1 + ΔH2 + ΔH3 + .... This is a restatement of ___ law.

Hess's

Which of the following substances would have a standard enthalpy of formation equal to 0 kJ/mol? Select all that apply.

Hg (l) H2 (g) Ar (g)

Generate the equation A + 2B → 2D from a combination of the reactions provided. Reaction 1: A + 2B → 2C Reaction 2: C → D How must reactions 1 and 2 be combined to sum to the overall reaction?

Reaction 1 + 2(Reaction 2)

Select the statement that correctly explains the source of the energy change in a chemical reaction.

The main contribution to ΔH is the difference in the bond energies of reactants and products.

The formation of an ionic compound involves the transfer of electrons. The removal of one or more electrons from a metal is a process that _____ energy, whereas the addition of one or more electrons to a nonmetal _____ energy.

absorbs; releases

By definition, the standard enthalpy of formation of a pure ___ in its standard state is equal to 0 kJ/mol.

element

The standard enthalpy of ___ is the change in enthalpy associated with the chemical reaction that generates 1 mole of a substance from its constituent ___ in their standard states.

formation; elements

The amount of energy required to separate 1 mole of ions in a crystalline solid into separate gaseous ions is called ___ energy. This energy is a measure of the total strength of the ___ bonds in the solid.

lattice; ionic

The standard enthalpy of formation of a compound is the enthalpy change associated with the reaction that generates ___ mole(s) of that compound from its component ___ when all of the substances are under ___ conditions.

one; elements; standards

The enthalpy of a reaction may be calculated using average bond enthalpies using an equation in which the energy _____ bonds form is subtracted from the energy _____ break bonds.

released when; required to

An element that is in its most stable form at ordinary atmospheric pressure is in its ___ state (usually signified by a degree sign).

standard

An element that is in its most stable form at ordinary atmospheric pressure is in its ______ state (usually signified by a degree sign).

standard

Hess's law states that the enthalpy change for an overall process (which can be broken into multiple steps) will be equal to the _____ of the enthalpy changes of its individual steps.

sum

Select the answer that best completes the following sentence: The bond enthalpy is ______.

the enthalpy change associated with breaking a particular bond in one mole of gaseous molecules

The standard enthalpy of formation, ΔHfo, is ______.

the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states

Consider the following reactions: A → 2B; ΔH = x kJ B → C; ΔH = y kJ What would be the enthalpy change associated with the reaction below? A → 2C

x + 2y

For the hypothetical reaction below, select the expression that would be equal to the enthalpy of the reaction. A-A + B-B → 2 A-B Bond Enthalpies: A-A = x B-B = y A-B = z

x + y - 2z

Consider the reaction shown. Select all the statements that correctly apply to the calculation of ΔH for this reaction using the bond energies provided.

ΔH for this reaction is equal to -168 kJ/mol. In this reaction, two C-Cl bonds are formed.

Select the correct form of the equation to find the enthalpy of a reaction from average bond enthalpies.

ΔH° = ΣBE(reactants) - ΣBE(products)