A chemical reaction is a process that rearranges the atomic structure of substances, leading to the formation of entirely new substances with different properties. The original substances that react are called reactants, and the new substances formed are called products. For example, when hydrogen gas (H₂) reacts with oxygen gas (O₂), they form water (H₂O). Here, H₂ and O₂ are reactants, and H₂O is the product.
How can we tell if a chemical reaction has taken place? Look for these common signs:
Chemical reactions are categorized based on how reactants transform into products.
Combination (Synthesis) Reaction: Two or more simple substances combine to form a more complex substance.
Decomposition Reaction: A complex substance breaks down into two or more simpler substances. This type of reaction often requires an input of energy, such as heat, light, or electricity.
Single Displacement (Substitution) Reaction: One element replaces another element in a compound. This typically occurs when a more reactive element displaces a less reactive one.
Double Displacement (Precipitation/Metathesis) Reaction: The positive ions (cations) and negative ions (anions) of two different ionic compounds exchange places, forming two new compounds. One of these products is often an insoluble solid (a precipitate), a gas, or water.
Combustion Reaction: A substance rapidly reacts with oxygen, usually producing heat and light. This is a common type of oxidation-reduction (redox) reaction.
The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction. This means the total number of atoms of each element must be the same on both the reactant and product sides of a chemical equation. Balancing an equation involves placing coefficients (whole numbers) in front of the chemical formulas to ensure this law is satisfied.
The process of baking a cake involves numerous chemical reactions; for instance, baking soda or powder reacts to produce carbon dioxide gas, causing the cake to rise. Similarly, the digestion of food in our bodies is a complex series of chemical reactions that break down nutrients. For a simple home practice, observe what happens when you mix baking soda and vinegar; note the evidence of a reaction and think about its type.
When you light a match, you see a flame, feel heat, and smell smoke. Based on this, what evidence suggests a chemical reaction is occurring? What type of reaction is the burning of the matchstick?