Measuring enthalpy change of solution Flashcards
What is standard enthalpy change of a solution?
The enthalpy change that takes place when 1 mole of compound is completely dissolved in water under standard conditions
What is the equation for enthalpy change of solution?
MX(s) + aq -> M⁺(aq) + X⁻(aq)
How do you find enthalpy change of solution by experiment?
- Add a known mass of ionic solid is enough water to dissolve it completely
- Measure initial temperature of the water and the final temperature
- When mass of solution is known, enthalpy change can be calculated
How do ionic substances dissolve?
1.Ionic lattice breaks up to release ions
2. Ions are attracted to, and bond with, the water molecules, forming the solution
How do ionic solids becomes aqueous?
Solid to gaseous ions -> gaseous to aqueous ions
How do ionic solids becomes aqueous?
Solid to gaseous ions -> gaseous to aqueous ions
What are the enthalpy changes when an ionic substance dissolves?
- Solid dissolves into water to form aqueous solution (enthalpy change of solution)
- Ionic solid breaks up into gaseous ions (reverse of lattice enthalpy)
- Gaseous ions turning into aqueous ions (enthalpy change of hydration)
What is the value of enthalpy change of solution?
Positive or negative depending on the relative sizes of lattice enthalpy and enthalpies of hydration
What is enthalpy change of hydration?
The enthalpy change that takes place when 1 mole of isolated gaseous ions is dissolved in water, forming 1 mole of aqueous ions under standard conditions
What are the equations for enthalpy change of hydration?
M⁺(g) + aq -> M⁺(aq)
X⁻(g) + aq -> X⁻(aq)
What is the value of enthalpy change of hydration?
Always negative because the gaseous ions are forming bonds with the water molecules
What is on the highest level of a Born-haber cycle?
Gaseous ions have more energy than other states
Where is the solid ionic compound on a Born-Haber cycle?
Lower enthalpy than gaseous ions
Where are aqueous ions on a Born-Haber cycle?
A lower enthalpy than gaseous ions
What is Hess’ law?
ΔsolH = ΔleH + Σ ΔhydH