Consider the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g). If 0.02 moles of PCl5, 0.04 moles of PCl3, and 0.08 moles of Cl2 are combined in a 0.5 L flask, what is the reaction quotient (Q) before the reaction ? g

The reaction quotient (Q) before the reaction is 0.32

Explanation:

Being the reaction:

aA + bB ⇔ cC + dD

where Q is the so-called reaction quotient and the concentrations expressed in it are not those of the equilibrium but those of the different reagents and products at a certain instant of the reaction.

The concentration will be calculated by:

You know  the reaction:

PCl₅ (g) ⇌ PCl₃(g) + Cl₂(g).

So:

The concentrations are:

[PCl₃]=[Cl₂]=[PCl₅]=

Replacing:

Solving:

Q= 0.32

The reaction quotient (Q) before the reaction is 0.32

There are a number of ways to express concentration of a solution. This includes molarity. Molarity is expressed as the number of moles of solute per volume of the solution. Calculations are as follows:

0.10 M NaCl = 0.10 mol NaCl/ L solution
mol NaCl = 0.10 mol NaCl/ L solution (0.100 L solution) = 0.01 mol NaCl
Mass of NaCl = 0.01 mol NaCl (58.44 g NaCl / 1 mol NaCl) = 0.5844 g NaCl

In order to make 100 mL of 0.10 M NaCl solution, you need to dissolve 0.5844 g of NaCl salt in water.