Which is false ?

Options

A. The greater the concentration of the substances involved in a reaction, the lower the speed of the reaction
B. The point of dynamic equilibrium is reached when the reaction rate in one direction just balances the reaction rate in the opposite direction
C. The dissociation of weak electrolyte is a reversible reaction
D. The presence of free ions facilitates chemical changes

Answer

To determine which statement is false among the given options regarding chemical equilibrium, we will analyze each option step by step.

### Step 1: Analyze Option A
**Statement:** "The greater the concentration of the substance evolved in the reaction, the lower the speed."

- **Explanation:** In a reversible reaction, if the concentration of products (substances evolved) increases, the rate of the forward reaction increases. This means that the speed of the reaction does not decrease; instead, it increases. Therefore, this statement is false.

### Step 2: Analyze Option B
**Statement:** "The point of dynamic equilibrium is reached when the reaction rate in one direction just balances the reaction rate in the opposite direction."

- **Explanation:** This statement is true. Dynamic equilibrium is achieved when the rates of the forward and backward reactions are equal. At this point, the concentrations of reactants and products remain constant.

### Step 3: Analyze Option C
**Statement:** "Dissociation of weak electrolyte is a reversible reaction."

- **Explanation:** This statement is true. Weak electrolytes do not completely dissociate in solution, and their dissociation can be reversed, making this a reversible reaction.

### Step 4: Analyze Option D
**Statement:** "The presence of free ions facilitates chemical changes."

- **Explanation:** This statement is also true. The presence of free ions in a solution can affect the rates of reactions and can shift the position of equilibrium, thus facilitating chemical changes.

### Conclusion
After analyzing all the options:
- **Option A** is false.
- **Options B, C, and D** are true.

Thus, the answer to the question "Which is false?" is **Option A**.

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