Chemical reactions are important processes that change substances into new products. To understand these reactions better, it's helpful to know some key features that define them.

Key Features of Chemical Reactions:

1. Reactants and Products:

   • In a chemical reaction, we start with substances called reactants. These reactants change to create products. For example, in the equation $A + B \rightarrow C + D$, $A$ and $B$ are the reactants, and $C$ and $D$ are the products.

2. Conservation of Mass:

   • The Law of Conservation of Mass tells us that the total mass of the reactants is the same as the total mass of the products. This means if we have a balanced equation, the number of atoms stays the same. For instance, if we start with 10 grams of reactants, we will still have 10 grams of products after the reaction.

3. Energy Changes:

   • Chemical reactions can change energy in different ways. Some reactions give off energy, called exothermic reactions, while others take in energy, called endothermic reactions. About 65% of reactions in living things, like how our cells get energy, are exothermic.

4. Reaction Rate:

   • The speed at which a reaction happens can change based on factors like temperature, concentration (how much of something there is), surface area, and whether a catalyst (a substance that speeds up the reaction) is present. For example, when the temperature goes up, many chemical reactions can happen twice as fast.

5. Chemical Equilibrium:

   • Some reactions can go both ways and reach a point called equilibrium. This means that the speed of the forward reaction is the same as the speed of the reverse reaction. We can describe this balance with a number called the equilibrium constant, $K$.

Knowing these features helps us group reactions into different types, like synthesis, decomposition, single-replacement, double-replacement, and combustion. Each type has its own unique traits and effects.