For each of these reactions, indicate the property which might be observed in order to determine when equilibrium has been reached.
a) PCl5(g) <--> PCl3(g) + Cl2(g)
b) CaCO3(s) <--> CaO(s) + CO2(g)
c) H2O(l) <--> H2O(g)
d) Cl2(g) + 2H2(g) H2(g) + 2HCl(g)
e) 2HBr(g) <--> H2(g) + Br2(g)
To determine when equilibrium has been reached in each of these reactions, you can observe certain properties that are associated with the state of equilibrium. Here are the properties for each reaction:
a) PCl5(g) <--> PCl3(g) + Cl2(g)
Property: Color change. The reaction involves a colorless gas (PCl5) and a yellowish-green gas (Cl2). When equilibrium is reached, the intensity of the yellowish-green color will be constant.
b) CaCO3(s) <--> CaO(s) + CO2(g)
Property: Mass change. The reaction involves a solid reactant (CaCO3) and a solid product (CaO) along with a gaseous product (CO2). As the reaction proceeds towards equilibrium, the mass of the solid reactant will decrease due to its conversion into products.
c) H2O(l) <--> H2O(g)
Property: Phase change. The reaction involves a liquid reactant (H2O) and a gaseous product (H2O). At equilibrium, a dynamic balance is established between the liquid and gaseous phases.
d) Cl2(g) + 2H2(g) <--> H2(g) + 2HCl(g)
Property: Change in color and concentration. The reaction involves the gases Cl2, H2, and HCl. When equilibrium is reached, the color of the mixture may change (Cl2 is yellow-green while HCl is colorless), and the concentrations of the reactants and products will become constant.
e) 2HBr(g) <--> H2(g) + Br2(g)
Property: Color change. The reaction involves a colorless gas (H2) and a reddish-brown gas (Br2). When equilibrium is achieved, the intensity of the reddish-brown color will remain constant.