Lattice Enthalpy Practice Questions - PDF

1. What is the standard enthalpy change of formation (ΔHf°)? * A) The enthalpy change when 1 mole of a substance is formed from its elements in their standard states. * B) The enthalpy change when 1 mole of a substance is burned completely in oxygen. * C) The enthalpy change when 1 mole of a substan...

1. What is the standard enthalpy change of formation (ΔHf°)? * A) The enthalpy change when 1 mole of a substance is formed from its elements in their standard states. * B) The enthalpy change when 1 mole of a substance is burned completely in oxygen. * C) The enthalpy change when 1 mole of a substance is dissolved in water. * D) The enthalpy change when 1 mole of a substance is broken down into its elements. 2. What is the standard enthalpy change of combustion (ΔHc°)? * A) The enthalpy change when 1 mole of a substance is formed from its elements in their standard states. * B) The enthalpy change when 1 mole of a substance is burned completely in excess oxygen under standard conditions. * C) The enthalpy change when 1 mole of a substance is dissolved in water. * D) The enthalpy change when 1 mole of a substance reacts with an acid. 3. What is the standard enthalpy of atomisation? * A) enthalpy change when 1 mole of atoms are formed into a compound * B) The enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state. * C) The enthalpy change when 1 mole of a compound is broken down into its elements. * D) The enthalpy change when 1 mole of solid is converted into a liquid. 4. What is the de nition of lattice enthalpy (ΔHlatt°)? * A) The enthalpy change when 1 mole of a solid ionic compound is formed from its constituent gaseous ions. * B) The enthalpy change when 1 mole of a solid ionic compound is dissolved in water. * C) The enthalpy change when 1 mole of a solid ionic compound is converted to its gaseous ions. * D) The enthalpy change when 1 mole of a solid ionic compound is melted. 5. Is lattice enthalpy (formation) exothermic or endothermic? * A) always endothermic fi * B) always exothermic * C) depends on the temperature * D) depends on the ionic compound 6. Which of the following factors *increases* the magnitude (makes more negative) of lattice enthalpy? * A) Larger ionic radii * B) Smaller ionic charges * C) Higher ionic charges and smaller ionic radii * D) Lower ionic charges and larger ionic radii 7. Which of the following compounds would you expect to have the most exothermic lattice enthalpy? * A) NaCl * B) MgO * C) KCl * D) MgCl2 8. What is the rst ionisation energy? * A) The energy required to remove 1 mole of electrons from 1 mole of gaseous 1- ions. * B) The energy released when 1 mole of gaseous atoms gains 1 mole of electrons. * C) The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms. * D) The energy released when 1 mole of electrons is removed from an atom. 9. What is the electron af nity? * A) The energy required to remove 1 mole of electrons from 1 mole of gaseous 1- ions. * B) The energy change when 1 mole of gaseous atoms gains 1 mole of electrons to form 1 mole of gaseous 1- ions. * C) The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms. * D) The energy released when 1 mole of electrons is removed from an atom. 10. What is the enthalpy change of hydration (ΔHhyd°)? * A) The enthalpy change when 1 mole of gaseous ions dissolves in fi fi water to form an in nitely dilute solution. * B) The enthalpy change when 1 mole of a solid ionic compound dissolves in water. * C) The enthalpy change when 1 mole of water is added to a solution. * D) The enthalpy change when 1 mole of a substance is hydrated. 11. What is the enthalpy change of solution (ΔHsol°)? * A) enthalpy change when 1 mole of water is added to a compound * B) The enthalpy change when 1 mole of solute dissolves in a solvent to form an in nitely dilute solution. * C) The enthalpy change when 1 mole of a substance is formed from its elements. * D) The enthalpy change when 1 mole of a substance is burned in oxygen. 12. Which equation correctly relates enthalpy of solution, lattice enthalpy (dissociation) and hydration enthalpies? * A) ΔHsol° = ΔHlatt° + ΣΔHhyd° * B) ΔHsol° = ΣΔHhyd° - ΔHlatt° * C) ΔHlatt° = ΔHsol° + ΣΔHhyd° * D) ΔHhyd° = ΔHsol° + ΔHlatt° 13. In a Born-Haber cycle, what is the direction of the arrow for an exothermic process? * A) Upwards * B) Downwards * C) To the right * D) To the left 14. Which enthalpy change is *always* endothermic? * A) Enthalpy of combustion * B) First ionisation energy * C) Electron af nity of chlorine * D) Enthalpy of hydration 15. The lattice enthalpy of dissociation of NaCl is +787 kJ mol-1. The enthalpy of hydration of Na+ is -406 kJ mol-1 and of Cl- is -364 kJ mol-1. What is the enthalpy of solution of NaCl? * A) +17 kJ mol-1 * B) -17 kJ mol-1 fi fi fi * C) +757 kJ mol-1 * D) +787 kJ mol-1 16. Which of the following correctly represents the rst ionisation energy of sodium? * A) Na(s) -> Na+(g) + e- * B) Na(g) -> Na+(g) + e- * C) Na(g) + e- -> Na-(g) * D) Na+(g) + e- -> Na(g) 17. Which of the following correctly represents the electron af nity of chlorine? * Cl(g) --> Cl-(aq) + e- * Cl(g) --> Cl-(g) + e- * C) Cl(g) + e- -> Cl-(g) * D) Cl2(g) + 2e- -> 2Cl-(g) 18. How would the numerical value of lattice enthalpy of formation for calcium oxide, CaO, compare with that for sodium oxide, Na2O? Assume the internuclear distance is approximately the same. The value for CaO would be * A) More endothermic * B) Less exothermic * C) More exothermic * D) The same 19. Born-Haber cycles are used to calculate which property? * A) Enthalpy of solution * B) Lattice enthalpy * C) Enthalpy of hydration * D) Electron af nity 20. For an endothermic reaction carried out at constant pressure, which statement is correct for the values of ΔH and heat transferred (q)? * A) ΔH > 0 and q < 0 * B) ΔH < 0 and q < 0 * C) ΔH > 0 and q > 0 * D) ΔH < 0 and q > 0 fi fi fi  Answers and Explanations: 1. A) The enthalpy change when 1 mole of a substance is formed from its elements in their standard states. - Correct de nition. 2. B) The enthalpy change when 1 mole of a substance is burned completely in excess oxygen under standard conditions. - Correct de nition. 3. B) The enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state. - This is the correct de nition. 4. C) The enthalpy change when 1 mole of a solid ionic compound is converted to its gaseous ions. - This is lattice enthalpy of *dissociation*. Lattice enthalpy of *formation* is the reverse, and is exothermic. 5. B) always exothermic - Lattice enthalpy of *formation* is always exothermic (energy is released when bonds are formed). 6. ** 5. B) always exothermic - Lattice enthalpy of *formation* is always exothermic (energy is released when bonds are formed). 6. C) Higher ionic charges and smaller ionic radii - Stronger electrostatic attraction leads to more exothermic lattice enthalpy. 7. B) MgO - Mg2+ and O2- have higher charges than the ions in the other compounds, leading to stronger attraction. 8. C) The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms. Correct de nition 9. B) The energy change when 1 mole of gaseous atoms gains 1 mole of electrons to form 1 mole of gaseous 1- ions.- Correct de nition 10. A) The enthalpy change when 1 mole of gaseous ions dissolves in water fi fi fi fi fi to form an in nitely dilute solution. - This is the de nition of enthalpy of hydration. 11. B) The enthalpy change when 1 mole of solute dissolves in a solvent to form an in nitely dilute solution. - This de nes enthalpy of solution. 12. A) ΔHsol° = ΔHlatt° + ΣΔHhyd° - This correctly shows that enthalpy of solution is the sum of lattice enthalpy of *dissociation* and the hydration enthalpies. 13. B) Downwards - Exothermic processes are conventionally shown with downward arrows in energy cycles. 14. B) First ionisation energy - It always requires energy to remove an electron from an atom. 15. A) +17 kJ mol-1 - ΔHsol° = +787 + (-406) + (-364) = +17 kJ mol-1 16. B) Na(g) -> Na+(g) + e- - Ionisation energy involves gaseous atoms. 17. C) Cl(g) + e- -> Cl-(g) - Electron af nity involves gaseous atoms gaining electrons. 18. C) More exothermic The charges on the ions in CaO are greater than in Na2O (+2 and -2, compared with +1 and -2). The increased electrostatic attraction would mean that the lattice enthalpy is more exothermic. 19. B) Lattice enthalpy - Born-Haber cycles are used to indirectly determine lattice enthalpies. 20. C) ΔH > 0 and q > 0 An endothermic reaction takes in energy from the surroundings in the form of heat and since energy has been taken in overall, the internal energy has increased; delta H, change in enthalpy, is positive. fi fi fi fi fi