Chem 0100 Q2

The product of the the following reaction is likely to be

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• 
• 
• 

For which of these reactions at 25^oC does the enthalpy change represent a standard enthalpy of formation?

• 2K(l) + Cl₂(g) → 2KCl(s)

• 2Na(s) + ¹/₂ O₂(g) → Na₂O(s)

• Mg²⁺(aq) + 2OH^-(aq) → Mg(OH)₂(s)

• C₆H₁₂O₆ → 6C(s) + 6H₂(g) + 3O₂(g)

Arrange the following compounds in order of increasing lattice energy: MgCl₂, LiCl, MgO, LiF

• LiF < MgO < MgCl₂ < LiCl

• LiCl < LiF < MgCl₂ < MgO

• MgCl₂ < LiCl < MgO < LiF

• LiF < MgCl₂ < MgO < LiCl

Given that the lattice energies of lithium chloride and potassium chloride are -864 and -718 kJ mol^-1 respectively, predict the value of the lattice energy of sodium chloride:

• ΔH_latt(NaCl) < -718 kJ mol^-1

• ΔH_latt(NaCl) > -864 kJ mol^-1

• 0 < ΔH_latt(NaCl) < -718 kJ mol^-1

• -718 kJ mol^-1 < ΔH_latt(NaCl) < -864 kJ mol^-1

Calculate the enthalpy of formation of calcium fluoride, ΔH from the following data: First ionization energy for calcium, ΔH = +590 kJ mol^-1, Second ionization energy from calcium, ΔH = +987 kJ mol^-1, Enthalpy of atomization of calcium, ΔH , = +178 kJ mol^-1, Enthalpy of atomization of fluorine, ΔH = +158 kJ mol^-1, Electron affinity of fluorine atoms, ΔH = -328 kJ mol^-1, Lattice energy of calcium fluoride, ΔH = -2630 kJ mol^-1

• - 1216 kJ mol^-1

• + 1373 kJ mol^-1

• - 1373 kJ mol^-1

• + 1216 kJ mol^-1

When 30 mL of 1.0 M HCl and 70 mL of 1.0 M NaOH are mixed in a Styrofoam cup, the temperature of the resulting solution changes from 20.0^oC to 26.5^oC. Calculate ΔH for the reaction in kJ mol^-1 of HCl. Assume that density of the solution is 1.0 g mL^-1 and the specific heat capacity of the solution is 4.18 J g^-1 K^-1.

• 18.1 kJ/mol

• 2717 kJ/mol

• -90.6 kJ/mol

• -603.8 kJ/mol

Calculate the enthalpy of hydrogenation of ethyne. The equation for the hydrogenation is: HC≡CH (g) + 2H₂ (g) C₂H₆ (g).

Assuming the following mean bond energies:

C≡C = 813 kJ mol-1

C–C = 346 kJ mol-1

C–H = 413 kJ mol-1

H–H = 436 kJ mol-1

• -1195 kJ mol^-1

• - 313 kJ mol^-1

• +1195 kJ mol^-1

• 313 kJ mol^-1

• +468 kJ mol^-1

• -268 kJ mol^-1

• -468 kJ mol^-1

• +268 kJ mol^-1

• -4546 kJ mol^-1

• - 106 kJ mol^-1

• +106 kJ mol^-1

• + 4546 kJ mol^-1

Consider the following reaction:

A(g) + B(g) → A⁺B^-(s)

Given the following data:

The proportionality constant, k = 2.22 x 10^-15 J pm

The distance between the centers of the two ions (A⁺ and B^-) = 350

The lattice energy involved in the reaction is:

• 3820 kJ/mol

• -3820 kJ/mol

• 8947 kJ/mol

• -8947 kJ/mol