Chemical Reactions

Basics of Chemical Reactions

  • A chemical reaction involves the transformation of one substance or multiple substances into one or more new substances.
  • The initial substances involved in a chemical reaction (before the reaction takes place) are known as reactants.
  • The new substances produced via a chemical reaction are referred to as products.

Balancing Chemical Equations

  • Chemical equations are used to represent chemical reactions.
  • They must be balanced, ensuring the number of atoms of each element is the same on both the reactants and products side. This principle follows the law of conservation of mass.
  • Chemical equations are balanced by adjusting the coefficients (the numbers in front of the symbols/chemical formula) rather than changing the subscript (number within the chemical formula).

Endothermic and Exothermic Reactions

  • Chemical reactions usually involve an energy change, with energy either being released or absorbed.
  • Endothermic reactions are chemical reactions that absorb energy from their surroundings. This energy is usually in the form of heat.
  • Examples of endothermic reactions include the process of photosynthesis in plants and the melting of ice into water.
  • Exothermic reactions are those that release energy, generally in the form of heat or light.
  • Everyday examples of exothermic reactions include burning a substance, neutralisation reactions (where an acid reacts with a base), and the reaction between water and calcium oxide.

Rate of Reactions

  • The rate of reaction describes how fast the reactants are transformed into products.
  • This rate can be influenced by several factors including concentration of reactants, temperature, surface area of solid reactants, and the presence of catalysts.
  • A catalyst is a substance that can speed up a chemical reaction by providing an alternative reaction pathway with a lower activation energy, but is not consumed in the reaction and can be used repeatedly.

Chemical Tests

  • Specific tests can be used to identify certain chemicals in a substance like the flame test for metal ions, or the litmus test for acids and bases.
  • Precipitation reactions (forming a solid in a solution) can also be a way to test for certain chemicals, such as using silver nitrate to test for chloride ions.