In the thermal decomposition of potassium chlorate given as `2KClO_(3)(s) to 2KCl(s)+3O_(2)(g)`, law of mass action

Options

A. Cannot be applied directly
B. Can be applied
C. Can be applied at low temperature
D. Can be applied at high temp. and pressure

Answer

To analyze the thermal decomposition of potassium chlorate using the law of mass action, we can follow these steps:

### Step 1: Write the balanced chemical equation
The balanced equation for the thermal decomposition of potassium chlorate is:
\[ 2 \text{KClO}_3 (s) \rightarrow 2 \text{KCl} (s) + 3 \text{O}_2 (g) \]

### Step 2: Identify the phases of the reactants and products
In this reaction, potassium chlorate (KClO3) and potassium chloride (KCl) are solids, while oxygen (O2) is a gas. The state of each substance is important when applying the law of mass action.

### Step 3: Apply the law of mass action
The law of mass action states that the rate of a reaction is proportional to the product of the concentrations of the reactants, each raised to the power of their coefficients in the balanced equation. For this reaction, since KClO3 and KCl are solids, their concentrations do not appear in the expression.

The rate of the forward reaction can be expressed as:
\[ \text{Rate} = k [\text{KClO}_3]^2 \]
However, since KClO3 is a solid, we typically do not include it in the equilibrium expression.

### Step 4: Write the equilibrium expression
For the decomposition reaction, the equilibrium expression is based only on the gaseous products:
\[ K = \frac{[\text{O}_2]^3}{1} \]
Where \( K \) is the equilibrium constant and the concentration of solids is not included.

### Step 5: Conclusion
The law of mass action can be applied to the thermal decomposition of potassium chlorate, but it is important to note that the concentrations of solids do not affect the equilibrium expression. Therefore, the law is more useful when considering the gaseous products.