Video Lecture 1: Lavoisier, Proust & The Laws of Chemical Combination

# Video Lecture 1: Lavoisier, Proust & The Laws of Chemical Combination
**Speaker:** Dr. Ananya Sharma | **Duration:** ~06:00 mins

### Introduction: The Quantitative Birth of Chemistry
In the late 18th century, Antoine Lavoisier transformed alchemy into exact quantitative science by measuring reactant and product masses on precision balances.

### 1. Law of Conservation of Mass (Lavoisier, 1774)
*Mass can neither be created nor destroyed in a chemical reaction.*
Total mass of reactants equals total mass of products:
$$\mathbf{\sum \text{Mass}_{\text{reactants}} = \sum \text{Mass}_{\text{products}}}$$
In an experiment reacting $5.3\text{ g}$ of sodium carbonate with $6.0\text{ g}$ of ethanoic acid: the products are $2.2\text{ g}$ of carbon dioxide gas, $0.9\text{ g}$ of water, and $8.2\text{ g}$ of sodium ethanoate. Total reactants $= 11.3\text{ g}$; total products $= 11.3\text{ g}$!

### 2. Law of Definite Proportions (Proust, 1799)
*In a chemical substance, the elements are always present in definite proportions by mass.*
Whether water is collected from the river Ganga, Arctic glaciers, or synthesized in a laboratory: water ($H_2O$) always contains hydrogen and oxygen in the fixed mass ratio of **$1 : 8$** ($2\text{ g H} : 16\text{ g O}$). Decomposing $9\text{ g}$ of water always yields $1\text{ g}$ of hydrogen and $8\text{ g}$ of oxygen!

### 3. Dalton's Atomic Theory (1808)
English schoolteacher John Dalton provided the theoretical framework explaining both laws:
1. All matter is made of tiny particles called atoms.
2. Atoms are indivisible particles that cannot be created or destroyed.
3. Atoms of a given element are identical in mass and chemical properties.
4. Atoms combine in the ratio of small whole numbers to form compounds!