thermal decomposition group 1/2

thermal decomposition

the breaking down of a compound using heat/the use of heat to break down a reactant into more than one product

what occurs when group 2 carbonates thermally decompose

group 2 carbonates decompose on heating to produce group 2 oxides and CO2

• MgCO3(S) → MgO(s) + CO2(g)

• Li2CO3(s)→ Li2O(s) + CO2 (g)

what is the trend of thermal decomposition down the group

it becomes harder to thermally decompose group2 carbonates down the group as more energy is required to overcome the bonds

why is it harder to thermally decompose carbonated down the group?

• ionic radius becomes larger

• therefore the charge density is lower

• lower polarising power

• the carbonate is more stable

THEREFORE LESS POLARISING POWER MEANS LESS DISTORTION ON THE CARBONATE ION (LESS WEAKENING OF C-O BONDS

why dont most group 1 carbonates thermally decompose

they only have a +1 charge so low charge density cannot polarise the carbonate ion

Lithium does thermally decompose

• Li2CO2 → Li2O + CO2

test for carbonate ease of decomposition

heat a known mass of carbonate in a boiling tube and pass the gas produced through lime water. Time for the first permanent cloudiness to appear in the limewater. Repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame.

what is formed when group 2 nitrates thermally decompose?

produce group2 oxides, oxygen & nitrogen dioxide

• 2Mg(NO3)2 → 2MgO + 4NO2 + O2 * GREATER DECOMPOSITION

what observations are made when g2 nitrates thermally decompose

• brown gas evolving

• white nitrate solid melts to a colourless solution & resoldifies

what products are formed when g1 nitrates thermally decompose except Li

2NaNO3 → 2NaNO2 + O2 LESSER DECOMPOSITION

sodium nitrate (V) → sodium nitrate (III)