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Questions and Answers
What is the enthalpy change of solution for ammonium nitrate when it dissolves in water?
What is the enthalpy change of solution for ammonium nitrate when it dissolves in water?
- +10 kJ mol–1
- -25.4 kJ mol–1
- 0 kJ mol–1
- +25.4 kJ mol–1 (correct)
Why does an instant cold pack become cold upon activation?
Why does an instant cold pack become cold upon activation?
- The chemical reaction is exothermic.
- It releases heat into the surroundings.
- The pack contains ice in addition to the ammonium nitrate.
- It absorbs heat from the surroundings. (correct)
Which of the following compounds is mentioned as an active ingredient in instant cold packs?
Which of the following compounds is mentioned as an active ingredient in instant cold packs?
- Calcium carbonate
- Sodium chloride
- Ammonium nitrate (correct)
- Ethanol
What happens to ammonium nitrate when a cold pack is activated?
What happens to ammonium nitrate when a cold pack is activated?
In addition to ammonium nitrate, which type of compounds can also have a defined standard enthalpy change of solution?
In addition to ammonium nitrate, which type of compounds can also have a defined standard enthalpy change of solution?
What is the role of the calorimeter in measuring enthalpy changes?
What is the role of the calorimeter in measuring enthalpy changes?
What happens to energy during the second electron affinity of oxygen?
What happens to energy during the second electron affinity of oxygen?
What does the relationship heat change = mcΔT represent in enthalpy change calculations?
What does the relationship heat change = mcΔT represent in enthalpy change calculations?
What is the purpose of the Born-Haber cycle in chemistry?
What is the purpose of the Born-Haber cycle in chemistry?
Which energy term is NOT typically included in a Born-Haber cycle?
Which energy term is NOT typically included in a Born-Haber cycle?
Why is it important to use excess of reactant B in calorimetry?
Why is it important to use excess of reactant B in calorimetry?
Which method requires the drawing of energy cycles to calculate enthalpy changes?
Which method requires the drawing of energy cycles to calculate enthalpy changes?
What effect does the adding of a second electron have on an anion during the second electron affinity?
What effect does the adding of a second electron have on an anion during the second electron affinity?
How can lattice energies be obtained using Hess's Law?
How can lattice energies be obtained using Hess's Law?
What is the primary benefit of using calorimetry in determining enthalpy changes?
What is the primary benefit of using calorimetry in determining enthalpy changes?
When constructing a Born-Haber cycle, which component is at the beginning of the cycle?
When constructing a Born-Haber cycle, which component is at the beginning of the cycle?
What does the term 'enthalpy change' (ΔH) refer to in a chemical reaction?
What does the term 'enthalpy change' (ΔH) refer to in a chemical reaction?
Which of the following factors must be controlled to ensure accurate calorimetry results?
Which of the following factors must be controlled to ensure accurate calorimetry results?
In a Born-Haber cycle, what is the relationship between enthalpy changes and lattice energy?
In a Born-Haber cycle, what is the relationship between enthalpy changes and lattice energy?
What is the initial step in the Born-Haber cycle for sodium chloride?
What is the initial step in the Born-Haber cycle for sodium chloride?
In the context of bond energies, which statement is accurate?
In the context of bond energies, which statement is accurate?
What is the enthalpy change of atomisation of aluminium?
What is the enthalpy change of atomisation of aluminium?
What is the first electron affinity of fluorine?
What is the first electron affinity of fluorine?
What is the calculated $ riangle H_{latto}$ for AlF3(s)?
What is the calculated $ riangle H_{latto}$ for AlF3(s)?
In the equation for the sum of enthalpy changes, what value corresponds to the enthalpy change of atomisation for aluminium?
In the equation for the sum of enthalpy changes, what value corresponds to the enthalpy change of atomisation for aluminium?
What is the formula used in calorimetry to calculate the enthalpy change when ΔT and mass are provided?
What is the formula used in calorimetry to calculate the enthalpy change when ΔT and mass are provided?
What is the enthalpy change of formation for calcium fluoride?
What is the enthalpy change of formation for calcium fluoride?
How is the lattice energy of calcium fluoride calculated in the Born–Haber cycle?
How is the lattice energy of calcium fluoride calculated in the Born–Haber cycle?
What is the first ionisation energy of calcium?
What is the first ionisation energy of calcium?
Which of the following represents the correct value of the electron affinity of fluorine?
Which of the following represents the correct value of the electron affinity of fluorine?
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Study Notes
Electron Affinity of Oxygen
- The second electron affinity of oxygen is endothermic.
- Adding a second electron to the negatively charged O− ion requires energy to overcome electron-electron repulsion.
Born–Haber Cycle
- An essential energy cycle used to calculate the lattice energy of ionic solids.
- Lattice energy cannot be directly measured; instead, it relates to several enthalpy changes during ionic solid formation.
- Key enthalpy changes involved include ionization energy, electron affinity, and enthalpy change of formation.
- The cycle illustrates energy changes through gaseous ions and atoms to solid ionic compounds.
Methods for Calculating Enthalpy Changes (ΔH)
- Calorimetry: Experimental method utilizing temperature change and mass to compute ΔH.
- Bond Energies: Values obtained from data booklets; typically used for simple covalent reactants and products.
- Hess’ Law: Involves drawing energy cycles, like Born–Haber cycles, to calculate ΔH indirectly.
Calorimeter Usage
- A calorimeter is used to measure enthalpy changes during reactions.
- The insulated design minimizes heat loss to the surroundings.
Instant Cold Packs
- Commonly contain ammonium nitrate, which undergoes an endothermic dissolution reaction.
- The process absorbs heat, making the pack cold, useful for treating injuries in situations where ice isn't available.
Worked Example of Born–Haber Cycle Calculation
- Illustration of calculating lattice energy using given enthalpy values for reactions involving calcium fluoride.
- The equation requires balancing energy changes to find unknown lattice energies based on Hess’ Law.
Energy Level Diagrams
- Alternative representation for reactions in Born–Haber cycles.
- Utilizes enthalpy changes of atomization and electron affinity to calculate the lattice energy of compounds.
Summary of Methods for Finding Enthalpy Change
- Calorimetry requires temperature change (ΔT) and mass, with the formula:
- ΔH = - (m * c * ΔT)
- Understanding these methods is crucial for thermal calculations in chemical processes.
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