Measuring enthalpy change of solution Flashcards

1
Q

What is standard enthalpy change of a solution?

A

The enthalpy change that takes place when 1 mole of compound is completely dissolved in water under standard conditions

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2
Q

What is the equation for enthalpy change of solution?

A

MX(s) + aq -> M⁺(aq) + X⁻(aq)

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3
Q

How do you find enthalpy change of solution by experiment?

A
  1. Add a known mass of ionic solid is enough water to dissolve it completely
  2. Measure initial temperature of the water and the final temperature
  3. When mass of solution is known, enthalpy change can be calculated
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4
Q

How do ionic substances dissolve?

A

1.Ionic lattice breaks up to release ions
2. Ions are attracted to, and bond with, the water molecules, forming the solution

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5
Q

How do ionic solids becomes aqueous?

A

Solid to gaseous ions -> gaseous to aqueous ions

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6
Q

How do ionic solids becomes aqueous?

A

Solid to gaseous ions -> gaseous to aqueous ions

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7
Q

What are the enthalpy changes when an ionic substance dissolves?

A
  1. Solid dissolves into water to form aqueous solution (enthalpy change of solution)
  2. Ionic solid breaks up into gaseous ions (reverse of lattice enthalpy)
  3. Gaseous ions turning into aqueous ions (enthalpy change of hydration)
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8
Q

What is the value of enthalpy change of solution?

A

Positive or negative depending on the relative sizes of lattice enthalpy and enthalpies of hydration

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9
Q

What is enthalpy change of hydration?

A

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

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10
Q

What are the equations for enthalpy change of hydration?

A

M⁺(g) + aq -> M⁺(aq)
X⁻(g) + aq -> X⁻(aq)

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11
Q

What is the value of enthalpy change of hydration?

A

Always negative because the gaseous ions are forming bonds with the water molecules

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12
Q

What is on the highest level of a Born-haber cycle?

A

Gaseous ions have more energy than other states

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13
Q

Where is the solid ionic compound on a Born-Haber cycle?

A

Lower enthalpy than gaseous ions

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14
Q

Where are aqueous ions on a Born-Haber cycle?

A

A lower enthalpy than gaseous ions

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15
Q

What is Hess’ law?

A

ΔsolH = ΔleH + Σ ΔhydH

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16
Q

What is the trend in enthalpy of hydration?

A

The more exothermic the enthalpy of hydration, the stronger the bonds formed between the ion and water molecules

17
Q

What is the effect of charge density on enthalpy of hydration?

A

The bonds between the ions and water are electrostatic so the higher the charge density of an ion, the stronger the bond

18
Q

What is the effect of ionic radius on enthalpy off hydration?

A

Ions with a smaller ionic radii (same charge) or more highly charged ions (smaller size) will have a more negative enthalpy of hydration