Consider the reaction. PCl 5 ( g ) − ⇀ ↽ − PCl 3 ( g ) + Cl 2 ( g ) K c = 0.0420 The concentrations of the products at equilibrium are [ PCl 3 ] = 0.170 M and [ Cl 2 ] = 0.280 M . What is the concentration of the reactant, PCl 5 , at equilibrium?

The concentration of the reaction PCl5 is 1, 133M

Explanation:

The equilibrium constant Kc is the ratio of the products to their reactants, each elevated with its stoichiometric coefficients. In this case:

Kc= (products)/(reactants)

Kc= (PCl3) x (Cl2) / (PCl5)

(PCl5)= (PCl3) x (Cl2)/ Kc = 0,170M x 0280 M/ 0,0420

(PCl5)= 1, 133 M

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.