5 Energetics - pedagogics.ca · 2 5 ENERGETICS CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY...
Transcript of 5 Energetics - pedagogics.ca · 2 5 ENERGETICS CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY...
5 ENERGETICS 1CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011
5 Energetics
Revision checklistI am able to:
state whether the temperature goes up or down and whether heat is given out or taken in an exothermic reaction
state the sign of ∆H for an exothermic reaction
state whether the products are more or less stable than the reactants in an exothermic reaction
draw enthalpy level diagrams for exothermic and endothermic reactions
state whether combustion is an exothermic or endothermic process
state whether the neutralisation reaction when an acid reacts with an alkali is an exothermic or endothermic process
calculate the enthalpy change when 1 mole of hexane is burnt, given that when 1.20 g of hexane (C6H14) is burnt the temperature of 250.0 g of water (speci� c heat capacity 4.18 J g−1 °C) is raised by 56.0 °C
give two reasons why the enthalpy change in the reaction described above is less exothermic than the literature value
describe an experimental procedure that could be used to measure the enthalpy change of a reaction occurring in aqueous solution
calculate the enthalpy change of neutralisation given that, when 200.0 cm3 of 0.150 mol dm−3 hydrochloric acid is mixed with 100.0 cm3 of 0.300 mol dm−3 sodium hydroxide solution the temperature rose by 1.36 °C
de� ne average bond enthalpy
write an equation to represent the bond enthalpy (energy) of hydrogen � uoride
state whether bond breaking is an exothermic or endothermic process
use the bond energies given below to calculate the enthalpy change for the reaction:
CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)
Bond Bond energy / kJ mol−1
H–Cl 430
C–Cl 340
C–H 410
Cl–Cl 240
explain in terms of bond enthalpies why the reaction above is exothermic
use the data below to calculate the enthalpy change for the process:
C2H5OH(l) → C2H5OH(g)
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) ∆H = −1371 kJ mol−1
C2H5OH(g) + 3O2(g) → 2CO2(g) + 3H2O(l) ∆H = −1415 kJ mol−1
de� ne the standard enthalpy change of formation for a substance
write an equation that represents the standard enthalpy change of formation of CH3COOH(l)
explain what is meant by the term ‘standard state’
state the standard conditions for enthalpy changes
write an equation that represents the standard enthalpy change of combustion of methanol (CH3OH(l))
HL
2 CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 20115 ENERGETICS
work out the standard enthalpy change of formation of benzene given the enthalpy change of combustion data below:
Substance Standard enthalpy change of combustion / kJ mol−1
hydrogen (g) −290
carbon (s) −400
benzene (l) −3300
calculate the standard enthalpy change of combustion of methanol using the standard enthalpies of formation, ∆Hf , below:
Compound CH3OH(l) CO2(g) H2O(g)
∆Hf / kJ mol−1 −240 −400 −240
de� ne the term ‘lattice enthalpy’
write an equation to represent the lattice enthalpy of sodium chloride
de� ne the term ‘electron a� nity’
write equations for the � rst and second electron a� nities of O
draw a Born–Haber cycle for the formation of sodium chloride and use it and the following data to calculate the standard enthalpy change of formation of sodium chloride:
∆Hat (Na) 100 kJ mol−1
∆Hat (Cl2) 120 kJ mol−1
IE (Na) 500 kJ mol−1
EA (Cl) −350 kJ mol−1
∆Hlatt (NaCl) 800 kJ mol−1
draw Born–Haber cycles for the formation of Na2O, CaO and MgCl2
place the following compounds in order of increasing lattice enthalpy:
KF MgCl2 MgF2 CaO CaS KI
explain why there is a signi� cant di� erence between the theoretical and experimental lattice enthalpy values for magnesium iodide
state and explain whether each of the reactions below involves an increase or decrease in entropy
NH3(g) + HCl(g) → NH4Cl(s)
C2H5OH(g) + 3O2(g) → 2CO2(g) + 3H2O(l)
2NO(g) + O2(g) → 2NO2(g)
state the sign of ∆S for each of the reactions above
use the absolute entropies given below to calculate the standard entropy change for the following reaction:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
Substance ∆S / J K−1 mol−1
CH4(g) 186
O2(g) 103
CO2(g) 214
H2O(l) 70
state whether ∆G is positive or negative for a spontaneous reaction
state the equation that connects ∆G to the enthalpy and entropy change of a reaction
HL
5 ENERGETICS 3CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011
calculate ∆G for the following reaction and state whether it is spontaneous or not at 298 K, given that ∆H = −2220 kJ mol−1 and ∆S = −370 J K−1 mol−1
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)
calculate ∆G for the following reaction given the ∆Gf values in the table:
C5H12(l) + 8O2 → 5CO2(g) + 6H2O(l)
Substance ∆Gf
C5H12(l) −10
H2O(l) −240
CO2(g) −400
explain whether a reaction for which ∆S is positive becomes more or less spontaneous as the temperature increases
work out the temperature at which the reaction below becomes spontaneous:
2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
∆H = + 600 kJ mol−1 ∆S = 900 J K−1 mol−1
HL