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Group 2 reactions with water

Hi

Can anyone help with these?......I really cannot work it out.....


Thanks so much for any help...... :smile:
Reply 1
Avatar for ghtrevgy
ghtrevgy
OP
3
Hi

Can anyone help with these?......I really cannot work it out.....


Thanks so much for any help...... :smile:
Reply 2
Avatar for SUSHI BOY
SUSHI BOY
seaspray
Hi

Can anyone help with these?......I really cannot work it out.....

Why is a metal oxide (not hydroxide) formed when Mg reacts with H2O as steam?
There is no liquid to stabilise the OH- ions.

seaspray
Why does Be not react with H2O?
Not sure, but it might be because Beryllium has a natural oxide layer.
Reply 3
Avatar for SUSHI BOY
SUSHI BOY
seaspray
Hi

Can anyone help with these?......I really cannot work it out.....

Why is a metal oxide (not hydroxide) formed when Mg reacts with H2O as steam?
There is no liquid to stabilise the OH- ions.

seaspray
Why does Be not react with H2O?
Not sure, but it might be because Beryllium has a natural oxide layer.
Reply 4
Avatar for hungry_hog
hungry_hog
9
i would compare the lattice enthalpies of Mg(OH)2 and MgO
i think you'll find MgO has a very high lattice enthalpy, thus the formation of MgO is favoured thermodynamically (very exothermic)

Mg has a protective oxide layer (MgO), hence the harsh conditions needed for the reaction

Be also has a protective oxide layer (BeO)
In addition to this it has higher 1st and 2nd ionisation energies than Mg, due to the smaller atomic radius. Or to put it another way, it takes more energy to remove two electons fron the 2s orbital in Be than the 3s orbital in Mg. I think this energy barrier is what prevents Be from reacting. I believe it does react with conc. H2SO4 though.
Reply 5
Avatar for hungry_hog
hungry_hog
9
i would compare the lattice enthalpies of Mg(OH)2 and MgO
i think you'll find MgO has a very high lattice enthalpy, thus the formation of MgO is favoured thermodynamically (very exothermic)

Mg has a protective oxide layer (MgO), hence the harsh conditions needed for the reaction

Be also has a protective oxide layer (BeO)
In addition to this it has higher 1st and 2nd ionisation energies than Mg, due to the smaller atomic radius. Or to put it another way, it takes more energy to remove two electons fron the 2s orbital in Be than the 3s orbital in Mg. I think this energy barrier is what prevents Be from reacting. I believe it does react with conc. H2SO4 though.
Reply 6
Avatar for Stranded
Stranded
11
but mg also has a protective layer of MgO...why, then, does it react with steam?
Reply 7
Avatar for Stranded
Stranded
11
but mg also has a protective layer of MgO...why, then, does it react with steam?
Reply 8
Avatar for hungry_hog
hungry_hog
9
hira89
but mg also has a protective layer of MgO...why, then, does it react with steam?


MgO not very soluble in water, but can be dissolved by steam

MgO(s) + H2O(g) --> Mg(OH)2(aq)

BeO completely insert to water and completely insoluble. Its essentially covalent.
BeO is not covalent

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