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What is the standard enthaply of formation?
- The enthalpy change that takes place when one mole of a compound is formed from it's constituent elements in their standard states under standard conditions
What is the standard enthalpy change of atomisation?
- The enthalpy change that takes place when one mole of gaseous ions forms from the element in it's standard state.
What is the the standard lattice enthalpy?
- The enthalpy change that takes place when one mole of an ionic compound is formed from its gaseous ions under standard conditions.
How does ionic charge affect lattice enthalpy?
- Higher charge means greater charge density.
- eg. Na+ and Mg2+.
- Means the lattice enthalpy is more negative.
- = stronger bonds formed.
How does ionic size affect lattice enthalpy?
- Smaller the ion means greater attraction between ions.
- Smaller ions attract more strongly because their charge density is higher.
Define a buffer solution.
- A solution that resists changes in pH when small amounts of acid or alkali are added.
- Works because of shifts in equilibreum.
How does a buffer solution resist change in pH if a small amount of acid is added?
- Most of the H+ ions combine with the weak acid ion A- from the weak acid salt.
- To form HA
- This shifts the equilibreum to the left reducing the [H+] to close to it's original value.
- Restoring pH
How does a buffer solution resist change in pH if a small amount of alkali is added?
- Most of the OH- ions react with H+ ions from the weak acid to form water.
- Causes more HA ions to dissociate to form H+ ions.
- The equilibreum shifts to the right meaning there is little change in [H+].
- So the pH is restored.
What the standard cell potentialbetween Cu and Zn be?
(aq) + 2e-
⇌ Cu (s)
- Biggest minus smallest.
- 0.34 --0.76 = 1.10
What would the metal ion half cell look like between Cu and Ag?
How is the hydrogen stored for a fuel cell?
- Liquid under pressure.
- Adsorbed on the surface of a solid metal.
- Absorbed within a solid material.
What is the overall reaction that takes place in a fuel cell?
H2 (g)+ 1/2 O2 (g) → H2O (l)
What is the reaction that takes place at the negative terminal of a hydrogen fuel cell?
- H2(g) + 2OH-(aq) → H2O (l) + 2e-
- Most negative
What is the reaction that takes place at the positive terminal of a hydrogen fuel cell?
(g) + H2
→ 2OH- (aq)
For a reaction to be feasible what must
Less than 0
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