1. Chemical Composition:
* Reactants: The substances that are present before the reaction takes place. They have their own unique chemical formulas and compositions.
* Products: The substances that are formed as a result of the chemical reaction. They have new and different chemical formulas and compositions compared to the reactants.
2. Chemical Bonds:
* Reactants: Have existing chemical bonds between their atoms.
* Products: Have new and different chemical bonds formed between atoms. This is the fundamental change that defines a chemical reaction.
3. Properties:
* Reactants: Possess specific physical and chemical properties, like melting point, boiling point, color, reactivity, etc.
* Products: Typically have different physical and chemical properties compared to the reactants. This difference in properties is often the basis for observing that a reaction has occurred.
4. Energy:
* Reactants: Have a certain energy level.
* Products: Have a different energy level than the reactants. Chemical reactions can either release energy (exothermic) or absorb energy (endothermic).
Example:
Consider the reaction of hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O):
Reactants: H₂ and O₂
Products: H₂O
* The chemical composition changes: Hydrogen and oxygen atoms are rearranged to form water molecules.
* The chemical bonds change: The bonds between hydrogen and oxygen atoms in the reactants are broken and new bonds between hydrogen and oxygen atoms are formed in the product.
* The properties change: Hydrogen and oxygen are gases at room temperature, while water is a liquid.
* Energy changes: This reaction releases energy (exothermic) and is accompanied by heat and light.
In summary:
Chemical reactions involve breaking and forming new chemical bonds, leading to the formation of products with different chemical compositions, properties, and energy levels compared to the reactants.
