Question

A sample of solid CaCO3 is added to an empty reaction vessel, which is then sealed. After awhile, the following reaction reaches a state of dynamic equilibrium.

CaCO3(s)---------> CaO(s) + CO2(g), H = 178 kJ (per mol CO2)

Briefly explain how the equilibrium values of the mass of CaO and the pressure of CO2 are affected by the

following actions.

a) increasing the temperature
b) removing a small amount, but not all, of the CaCO3
c) transferring the equilibrium mixture to a larger reaction vessel
d) adding a small amount of LiOH(s), which reacts with CO2 to give Li2CO3(s) and H2O(l)

Answer 1

A)  Calcination reactions usually take place at or above the thermal decomposition temperature (for decomposition and volatilization reactions) or the transition temperature (for phase transitions). This temperature is usually defined as the temperature at which the standard Gibb's free energy of reaction for a particular calcination reaction is equal to zero. For example, in limestone calcination, a decomposition process, the chemical reaction is CaCO3 = CaO + CO2(g). The standard Gibb's free energy of reaction is approximated as ΔG°r = 177,100 - 158 T (J/mol). The standard free energy of reaction is zero in this case when the temperature, T, is equal to 848°C.

Examples of chemical decomposition reactions common in calcination processes, and their respective thermal decomposition temperatures include:

CaCO3 = CaO + CO2; 848°C

B) If you remove small amount of CaCO3 it will not effect much on equilibrium. Still reaction will slower.

C) If you have transfer the reaction mixture in larger vessel, area will change and pressure in that vessel will change it will affect the reaction.