"The resultant heat change in a reaction is the same whether it takes place in one or several stages." This statement is called

Options

A. Lavoisier and Laplace law
B. Hess's law
C. Le-chatelier principle
D. Joule's law

Answer

The statement "The resultant heat change in a reaction is the same whether it takes place in one or several stages" is known as Hess's Law. Let's break down the reasoning step by step:

### Step-by-Step Solution:

1. **Understanding the Statement**: The statement indicates that the total heat change (ΔH) for a chemical reaction is independent of the pathway taken to achieve that reaction. This means whether the reaction occurs in one step or multiple steps, the total heat change remains the same.

2. **Single-Step Reaction**: Consider a reaction that occurs in a single step, for example, A → D. The heat change associated with this reaction can be denoted as ΔH.

3. **Multi-Step Reaction**: Now, consider the same reaction occurring in multiple steps:
- Step 1: A → B (with heat change ΔH1)
- Step 2: B → C (with heat change ΔH2)
- Step 3: C → D (with heat change ΔH3)

4. **Total Heat Change in Multi-Step Reaction**: According to the multi-step process, the total heat change for the reaction A → D can be expressed as:
\[ ΔH = ΔH1 + ΔH2 + ΔH3 \]

5. **Conclusion**: The equality of the heat changes in both scenarios leads to the conclusion that the total heat change for the reaction is the same regardless of whether it occurs in one step or multiple steps. This principle is formally known as Hess's Law.

6. **Final Answer**: Therefore, the statement is called Hess's Law.