Introduction for Reactions

Chapter: Introduction for Reactions

Understanding Basic Terms

  • A chemical reaction can be described as the process of transforming one material (reactant) into another (product).
  • Every chemical reaction is accompanied by an energy change because of breaking and forming bonds.
  • A reactant plays a vital part in a chemical reaction. It’s what is used at the beginning of a reaction.
  • Products are the substances formed by the reaction.
  • An equation represents a chemical reaction using symbols and formulae.

Types of Chemical Reactions

  • Combustion Reaction: A reaction that occurs when a substance reacts with oxygen, releasing energy in the form of light and heat.
  • Synthesis Reaction: Two or more simple substances combine to form a more complex substance.
  • Decomposition Reaction: The breakdown of a complex substance into two or more simpler substances.
  • Single Replacement Reaction: A reaction where one element is replaced by another in a compound.
  • Double Replacement Reaction: The ions of two compounds exchange places in an aqueous solution to form two new compounds.

Balancing Chemical Equations

  • Balanced equations show that matter cannot be created or destroyed in a chemical reaction. The numbers of atoms of each element must be the same on both sides of the equation.
  • It’s important to remember to balance the equation to show conservation of mass.
  • Compounds are represented by their chemical formulae in the equation.
  • The coefficients in a balanced equation represent the number of each type of particle - atoms, ions or molecules - involved in a reaction.

Physical and Chemical Changes

  • A physical change is a reversible change that doesn’t change the chemical nature of the substance.
  • A chemical change alters the substance’s chemical makeup, and it is generally not reversible by physical means.

Energy in Reactions

  • During a reaction, energy can either be taken in from the surroundings (endothermic reaction) or released to the surroundings (exothermic reaction).
  • Exothermic reactions release energy in the form of heat.
  • Endothermic reactions absorb energy from their surroundings.
  • The activation energy is the minimum amount of energy that particles must have for a reaction to occur.