The Kc value is called the ___________ ___________ or the Qc.

The Kc value is called the ___________ ___________ or the Qc.

• A. reaction quotient
• B. equilibrium constant
• C. rate constant
• D. activation energy

Answer: (A)

The idea to focus on is how the reaction quotient and the equilibrium constant relate. Both use the same expression: concentrations of products raised to their stoichiometric powers divided by concentrations of reactants raised to their powers. The reaction quotient, Qc, is that ratio calculated at any moment in time. The equilibrium constant, Kc, is the value of that same ratio when the system has reached equilibrium. When equilibrium is reached, Qc equals Kc. So the quantity describing the current state with live concentrations is the reaction quotient, and at equilibrium it becomes the Kc value. That’s why the phrasing links Kc with the reaction quotient or Qc.

The idea to focus on is how the reaction quotient and the equilibrium constant relate. Both use the same expression: concentrations of products raised to their stoichiometric powers divided by concentrations of reactants raised to their powers. The reaction quotient, Qc, is that ratio calculated at any moment in time. The equilibrium constant, Kc, is the value of that same ratio when the system has reached equilibrium. When equilibrium is reached, Qc equals Kc. So the quantity describing the current state with live concentrations is the reaction quotient, and at equilibrium it becomes the Kc value. That’s why the phrasing links Kc with the reaction quotient or Qc.