How does li have high hydration enthalpy but does not react vigorously with water?
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All the elements of Group 1 react vigorously with water to give metal hydroxides and liberate hydrogen gas, but this reactivity increases down the group.
Lithium's density is only about half that of water, so it floats on the surface and ultimately disappears, giving off hydrogen gas and forming a colourless solution of lithium hydroxide. But unlike the rest of the s-block elements, this reaction is not vigorous.
2Li(s)+2H2O(l)→2LiOH(aq)+H2(g)
Using Hess’s Law, we can split it into several theoretical steps with known enthalpy changes.
Atomisation energy:
Li(s)→Li(g); ∆H=+ve
Ionisation energy:
Li(g)→Li+(g)+e−; ∆H=+ve
Hydration enthalpy:
Li+(g)→Li+(aq); ∆H=-ve
Lithium's density is only about half that of water, so it floats on the surface and ultimately disappears, giving off hydrogen gas and forming a colourless solution of lithium hydroxide. But unlike the rest of the s-block elements, this reaction is not vigorous.
2Li(s)+2H2O(l)→2LiOH(aq)+H2(g)
Using Hess’s Law, we can split it into several theoretical steps with known enthalpy changes.
Atomisation energy:
Li(s)→Li(g); ∆H=+ve
Ionisation energy:
Li(g)→Li+(g)+e−; ∆H=+ve
Hydration enthalpy:
Li+(g)→Li+(aq); ∆H=-ve
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In reaction with water is less vigorous than that of sodium which has the least negative E0 value among the alkali metals. This behaviour of lithium is attributed to its small size and very high hydration energy.
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