Enthalpy of hydration

  • Thread starter broegger
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  • #1
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Hi.

How come that Cs reacts more violently with water than Li, when the enthalpy of hydration for Li is -520 kJ/mol while it is only -276 kJ/mol for Cs. More energy is released in the Li reaction, but still it reacts more quietly?

(EDIT: Oops, maybe this should be in the homework section?)
 

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  • #2
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What else affects the reaction? It ain't ALL enthalpy of hydration.
 
  • #3
GCT
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Yes, for instance, consider the radii of the elements.
 
  • #4
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There will occur a redoxreaction when Li and Cs are put in water. What happens in this reaction with Li and Cs in this redoxreaction ? In combination to the previous post it should answer your question.
 
  • #5
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The Li atoms are smaller, but how does that affect the reaction?
 
  • #6
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broegger said:
The Li atoms are smaller, but how does that affect the reaction?

compare:

Li --> Li(+) + e(-) and Cs --> Cs(+) + e(-)

in what electron lies more energy ? and what electron is easiest being lost ?
 
  • #7
Gokul43201
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How on earth do you spec an enthalpy of hydration for an atomic species (like Li or Cs)? What does that even mean? Would you (the OP) please define the enthalpy of hydration in this context?

Secondly, translate the words "violently" and "quietly" into terms involving well-defined physical quantites. The answer will pop right out.
 
  • #8
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I have no idea, just quoting from the book, basically. Doesn't Li- and Cs-solids exist? I'm a lousy chemist, I know.

I would think that "quietly" means slow and "violently" means fast, so the statement is that the reaction rate of Cs + water is larger than the reaction rate of Li + water. I understand that the reaction rate is influenced by other factors than the difference in enthalpy...
 
  • #9
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Okay --- step at a time: what's the first thing that happens when elemental Li or Cs are placed in contact with water? (Yes, they're both solids.)
 
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  • #10
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Gokul43201 said:
How on earth do you spec an enthalpy of hydration for an atomic species (like Li or Cs)? What does that even mean? Would you (the OP) please define the enthalpy of hydration in this context?

Secondly, translate the words "violently" and "quietly" into terms involving well-defined physical quantites. The answer will pop right out.

the topic starter said: 'reacts more violently with water'

--> thus we speak about the reaction between elemental Li /Cs and water, i assume.
 

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