Chem 12 IB – HL Energetics Review
1 Distinguish between the terms ionization energy and electron affinity.
2 Write an equation to represent each of the following enthalpy terms.
a Enthalpy of atomization of potassium
b Enthalpy of dissociation of bromine gas
c First ionization energy of potassium
d First electron affinity of bromine
e Enthalpy of formation of potassium bromide
f Lattice enthalpy of potassium bromide
3 Complete the following Born–Haber cycle for sodium oxide.
4 The lattice enthalpy of rubidium chloride, RbCl, can be determined using a Born–Haber cycle. Use the data in the table below to construct a Born–Haber cycle and determine a value for the lattice enthalpy of rubidium chloride.
5 Consider each of the following pairs and explain which compound you would expect to have the greater lattice enthalpy.
a KCl or KI
b MgO or MgS
c BaO or MgO
d LiF or CsF
e KCl or CaCl2
6 Describe the assumption that is made in determining theoretical lattice enthalpy values.
7 Explain why the experimental lattice enthalpy for an ionic compound is generally greater than the theoretical lattice enthalpy.
8 Consider the following values of theoretical and experimental lattice enthalpies and then deduce the order of increasing covalent character for the following ionic compounds.
9 Considering the theoretical and experimental lattice enthalpies shown in the table below, compare the bonding in sodium chloride and silver chloride.
10 Arrange the following in order of increasing entropy.
I) 1 mol H2O(l) at 100°C, 101.3 kPa
II )1 mol H2O(s) at 0°C, 101.3 kPa
III )1 mol H2O(l) at 0°C, 101.3 kPa
IV )1 mol H2O(g) at 100°C, 101.3 kPa
V )1 mol H2O(l) at 25°C, 101.3 kPa
11 For each reaction, state whether it has a positive or negative entropy change.
a N2(g) + 3H2(g) → 2NH3(g)
b N2O4(g) → 2NO2(g)
c HCl(g) + NH3(g) → NH4Cl(s)
d CaCO3(s) → CaO(s) + CO2(g)
e C4H8(g) + 6O2(g) → 4CO2(g) + 4H2O(g)
12 Arrange the following reactions in order of increasing entropy change.
I COCl2(g) → CO(g) + Cl2(g)
II PCl3(g) + Cl2(g) → PCl5(g)
III C6H12(l) + 9O2(g) → 6CO2(g) + 6H2O(g)
IV C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)
13 Describe how the entropy of water changes as it condenses from steam to liquid water, and then use Appendix 3 (Chang) to calculate the entropy change for the reaction:
H2O(g) → H2O(l)
14 Using Appendix 3 (Chang), calculate the standard entropy change for each of the following equations.
a C4H8(g) + 6O2(g) → 4CO2(g) + 4H2O(g)
b 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g)
c C2H4(g) + H2(g) → C2H6(g)
d 2SO2(g) + O2(g) → 2SO3(g)
15 The following reaction is only spontaneous at ‘high’ temperatures:
N2 (g) + O2(g) → 2NO(g)
If ΔH = +180.8 kJ mol−1 and ΔS = +24.7 J K−1 deduce the temperature at which the reaction begins to be spontaneous.
16 Using data from Appendix 3, calculate the temperature at which the transformation of H2O(l) to H2O(g) is spontaneous.
17 Using values in Appendix 3, calculate the standard free energy of reaction for the following reactions.
a CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
b C2H4(g) + H2(g) → C2H6(g)
c CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)
18 Calculate ΔGrxn, using values for the standard free energy of formation, and compare the answer with that calculated using ΔG = ΔH – TΔS for the reaction N2(g) + O2(g) → 2NO(g) at 298 K. (ΔH = +180.8 kJ mol1 and ΔS = +24.7 J K−1)
19 The standard enthalpy change of combustion of ethanal, CH3CHO(l), is −1167 kJ mol−1. Given the information in Appendix 3, calculate the standard enthalpy change of formation of ethanal.
20 Using values from table 4.1.1, calculate the standard enthalpy of combustion for propene, given the equation for the reaction:
2C3H6(g) + 9O2(g) → 6CO2(g) + 6H2O(g)