Final answer:
The value of q, or the reaction quotient, for a reaction that begins with only products, is a very large number, indicating the reaction may proceed in the reverse if reactants appear, moving it towards equilibrium.
Step-by-step explanation:
The value of q or the reaction quotient, for a reaction with only products, such as the oxidation of sulfur dioxide (2SO2(g) + O₂(g) ⇒ 2SO3(g)), would be a very large number because there are no reactants present to be included in the calculation of Q. The reaction quotient Q is calculated based on the concentrations of the products and reactants at any point during the reaction. In this scenario, where we start with only product SO3, the concentration of reactants (SO2 and O2) would be zero. Since these reactants' concentrations appear in the denominator of the reaction quotient equation, this would make Q effectively infinity.
It is assumed that the reaction can proceed in the reverse direction if reactants were introduced. The arithmetic sign of Q is positive because concentrations of products and reactants are always positive values or zero; hence, Q can never be negative. If the value of Q is significantly larger than the equilibrium constant (K), this indicates the reaction will proceed in the reverse direction towards equilibrium, converting products back into reactants.