Q17.38P - Chemistry: Molecular Nature Of Matter And Change

Question

In the 1980s, CFC-11 was one of the most heavily produced chlorofluorocarbons. The last step in its formation is 

${\mathbf{CCI}}_{\mathbf{4}\mathbf{\left(}\mathbf{g}\mathbf{\right)}}\mathbf{+}{\mathbf{HF}}_{\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{ }}\mathbf{ }\mathbf{ }\mathbf{\square }\mathbf{ }\mathbf{ }\mathbf{ }{\mathbf{CFCI}}_{\mathbf{3}\mathbf{\left(}\mathbf{g}\mathbf{\right)}}\mathbf{+}{\mathbf{HCI}}_{\mathbf{\left(}\mathbf{g}\mathbf{\right)}}$

If you start the reaction with equal concentrations of ${\mathbf{CCI}}_{\mathbf{4}}$ and HF, you obtain

equal concentrations of ${\mathbf{CFCI}}_{\mathbf{3}}$ and HCl at equilibrium. Are the final

concentrations of ${\mathbf{CFCI}}_{\mathbf{3}}$and HCl equal if you start with unequal 

concentrations of ${\mathbf{CCI}}_{\mathbf{4}}$ and HF? Explain.

Step-by-Step Solution

Answer

The equilibrium concentrations of ${\mathrm{CFCI}}_3$ and HCl are equal for any initial

concentrations of ${\mathrm{CCI}}_4$ and HF. This is due to equal stoichiometric coefficients for 

${\mathrm{CFCI}}_3$and HCl in the balanced equation.

Step 1: What was CFC-11?

CFC-11 is a strong greenhouse gas that depletes the ozone layer and is widely employed as a refrigerant in building chillers, a foam blowing agent in insulating foams, and a solvent. And CFC-11 emissions from eastern China showed that emissions from temperate western Asia and tropical Asia were growing significantly.

Step 2: Explanation for this topic

Rewrite the reaction as follows:

${\mathrm{CCI}}_{4\left(\mathrm{g}\right)}+{\mathrm{HF}}_{\left(\mathrm{g}\right) }\square {\mathrm{CFCI}}_{3\left(\mathrm{g}\right)}+{\mathrm{HCI}}_{\left(\mathrm{g}\right)}$

Assume the initial concentration ${\mathrm{CCI}}_4$ is y (M), and the initial concentration of HF is z 

(M).

Assume x (M) of ${\mathrm{CCI}}_4$and x (M) of HF dissociate and the construct ICE table as

follows:

Concentration	${\mathrm{CCI}}_{4\left(\mathrm{g}\right)}+{\mathrm{HF}}_{\left(\mathrm{g}\right) }\square {\mathrm{CFCI}}_{3\left(\mathrm{g}\right)}+{\mathrm{HCI}}_{\left(\mathrm{g}\right)}$
Initial (M)	Y	Z	0	0
Change (M)	-x	-x	+x	+x
Equilibrium (M)	y-x	z-x	X	x

Equilibrium concentrations of ${\mathrm{CFCI}}_3$ and HCl are equal for any initial concentrations

of ${\mathrm{CCI}}_4$ and HF. This is due to equal stoichiometric coefficients for ${\mathrm{CFCI}}_3$and HCl in

the balanced equation.