Thermal Stability of Group 2 Compounds Flashcards
what is thermal stability
the measure of how stable a compound is when heated
what would be the extremes of a compounds thermal stability
- not decomposing at all (very stable)
- decomposing as much as possible (very unstable)
when you melt a group 1 halide, it is thermally decomposing or not and why
- it isnt
- because you are simply separating the ions from their giant lattice to being in a fluid state
- therefore nothing is decomposed simply due to its change of state
when group 2 nitrates or carbonates are heated, do they melt or decompose
they decompose
what three factors make group 2 compounds different from group 1 compounds
- charge on group 2 cation is double that of a group 1 cation
- the ionic radius of group 2 cations are smaller than group 1’s (increase in nuclear charge)
- nitrate and carbonate ions are more complex than halide ions
why do group 2 nitrates decompose when heated
- because its more complex it can change into smaller and more stable ions
- like NO2- or O^2-
- in which they an decompose and release oxygen or nitrogen dioxide gas
why do group 2 carbonates decompose when heated
- its more complex so it can change into a smaller and more stable ion
- like O^2-
- which would decompose and react with the carbon to form CO2
how does the difference between the group 1 and 2 charges and atomic radii play a role in the stabilities of the anions
- the stabilities of NO3- and CO3^2- decrease with the increasing charge of the anion
- stability also decreases with the decrease in atomic radius
- so the group 2 cations affect the anions more
what observational similarity do all group 1 and 2 nitrates have in common
they are all white solids
what products are formed when the nitrates are heated and decompose
- they decompose to nitrites and oxides
- so they give off nitrogen dioxide and oxygen
what other product will be formed if the nitrate contains water of crystallisation
steam (H2O)
what does nitrogen dioxide look like
brown fumes
if no brown fumes are given off, what would be the work equation for the decomposition of a metal nitrate instead
metal nitrate = metal nitrite + oxygen
what is the difference between nitrates and nitrites
- nitrate = nitrate(V) or +5
- nitrite = nitrate(III) or +3
what would the equation be for the complete decomposition of a metal nitrate
metal nitrate = metal oxide + nitrogen dioxide + oxygen
what would the results of heating every group 1 nitrate be with the result being either brown fumes or no fumes
- lithium nitrate would produce brown fumes
- the rest wouldnt
what would the results of heating every group 2 nitrate be with the result being either brown fumes or no fumes
all of them would produce brown fumes
what would the results of decomposing every group 1 and 2 nitrate therefore be, with the results being either greater or lesser decomposition
- only lithium nitrate in group 1 would go through greater decomposition
- the rest of group 1 would go through lesser
- then all of group 2 would go through greater
why is lithium nitrate an exception to the pattern
- the stabilities of the anions decrease if the size of the cation decreases
- lithium is the smallest cation out of all of them
- this is significant enough for it to have greater decomposition
what do all group 1 and 2 carbonates look like
white solids
why can no observations be made during the decomposition of carbonates
- because the product, CO2, is colourless
- and the carbonate and oxide ions formed are also white
what would the results of decomposing every group 1 and 2 carbonate be, with the results being decomposition or no decomposition
- lithium carbonate is the only group 1 carbonate that decomposes
- all of the group 2 carbonates decompose
what does lithium carbonate decompose to
- Li = 1+ and CO3 = 2- so Li2CO3
- Li2CO3 = Li2O + CO2
what is the general equation for the decomposition of metal carbonates, using M
MCO3 = MO + CO2
