Chemical Reaction
1. What’s a Chemical Reaction?
A chemical reaction happens when one or more substances change into completely new ones. The particles of the reactants rearrange their atoms to form new bonds, creating products with different physical and chemical properties. For example:
2H2+O2→2H2O2H_2 + O_2 → 2H_2O2H2+O2→2H2O
Here, hydrogen and oxygen (gases) react to form water (a liquid) — totally new properties!
2. Reactants & Products
Reactants → the starting substances (what you begin with).
Products → the new substances formed after the reaction. Example:In the reaction Mg + HCl → MgCl₂ + H₂,
Reactants: magnesium (Mg) and hydrochloric acid (HCl)
Products: magnesium chloride (MgCl₂) and hydrogen gas (H₂)
3. Law of Conservation of Mass
No matter what kind of reaction you do, mass is conserved. That means the total mass of all reactants equals the total mass of all products — nothing is lost or gained, it’s just rearranged. Example: burning paper doesn’t “destroy” it — the carbon combines with oxygen to form CO₂ and ash; the total mass (if you include gases) stays the same.
4. Energy Changes
Every chemical reaction involves energy — bonds breaking need energy, and bonds forming release energy.
Exothermic reactions: release energy (usually heat or light). Example: burning wood
Endothermic reactions: absorb energy from surroundings. Example: photosynthesis
5. Indicators of a Chemical Reaction
When a chemical reaction happens, you’ll often notice some signs or clues that something new is being formed. Here are the big ones
6. Rate of Reaction
The rate of reaction means how fast or slow a reaction takes place. Some reactions happen instantly (like explosions ), others take forever (like rust forming ).
Wikipedia Writing
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.[1]When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nucleus(no change to the elements present), and can often be described by a chemical equation. Nuclear Chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and Radioactive elements where both electronic and nuclear changes can occur.