Mass action rato or reaction quotient Q for a reaction can be calculate using the law of masss action
`A(g)+B(g) hArr C(g)+D(g)`
`Q=([C][D])/([A][B])`
The value of Q decides whether the reaction is at equilibrium or not.
At equilibrium, `Q=K`
For an equilibrium process, `Q ne K`
when `Q gt K`, reaction will favour backward direction and when `Q lt K`, it will favour direction.
Answer the following questions:
The reaction quotient Q for:
`O_(2)(g)+2H_(2)(g) hArr 2H_(2)O(g)`
is given by `Q=([H_(2)O]^(2))/([O_(2)][H_(2)]^(2))`. The reaction will proceed in backward direction, when

Options

A. `Q=K_(c)`
B. `Q lt K_(c)`
C. `Q gt K_(c)`
D. `Q=0`

Explanation

To determine when the reaction will proceed in the backward direction for the given reaction:

**Reaction:**
\[ O_2(g) + 2H_2(g) \rightleftharpoons 2H_2O(g) \]

**Step 1: Write the expression for the reaction quotient (Q).**
The reaction quotient \( Q \) is calculated using the concentrations of the products and reactants at any point in time. For the given reaction, the expression for \( Q \) is:

\[ Q = \frac{[H_2O]^2}{[O_2][H_2]^2} \]

**Step 2: Understand the relationship between Q and K.**
The equilibrium constant \( K \) is a specific value of \( Q \) when the reaction is at equilibrium. If \( Q = K \), the system is at equilibrium. If \( Q \neq K \), the system will shift to reach equilibrium.

**Step 3: Determine the conditions for the backward reaction.**
The reaction will favor the backward direction (the formation of reactants from products) when the reaction quotient \( Q \) is greater than the equilibrium constant \( K \). This indicates that there are too many products relative to the reactants, and the system will shift left to produce more reactants.

**Conclusion:**
The reaction will proceed in the backward direction when:

\[ Q > K \]