Chemistry Pointers

• Chemistry


  The science that deals with the properties, composition and structures of matter, the changes it undergoes, and the laws and principles which govern these changes
• Main branches of chemistry


  • Organic Chemistry
  • Inorganic Chemistry
  • Analytical Chemistry
  • Physical Chemistry
  • Biochemistry
• Organic Chemistry


  Mostly concerned with the study of chemicals containing the element carbon
• Inorganic Chemistry


  The study of all elements and compounds other than organic compounds
• Analytical Chemistry


  The study of qualitative (What is present?) and quantitative (How much is present?) analysis of elements and compounds
• Physical Chemistry


  The study of reaction rates, mechanisms, bonding and structure, and thermodynamics
• Biochemistry


  The study of the chemical reactions that happen within the biological process
• Matter


  Anything that occupies space and has mass
• Forms of matter


  • Substances
  • Mixtures
• Types of substances


  • Elements
  • Compounds
• Types of mixtures


  • Homogeneous
  • Heterogeneous
• Types of elements


  • Metals
  • Nonmetals
  • Metalloids
• Physical properties


  Properties of matter that do not change as it is being observed
• Types of physical properties


  • Intrinsic
  • Extrinsic
• Intrinsic properties


  Properties that distinguish a substance from another substance
• Extrinsic properties


  Properties that depend on the amount of matter observed
• Albert Einstein proved that an increase in mass generates an increase in energy and a decrease in mass generates a decrease in energy
• Physical change


  When only the physical properties of a substance change
• Chemical change


  When the identity of the substance is altered, producing new kinds of matter
• In a chemical change (chemical reaction), the mass of the reactants is always the same as the mass of the products. This is called the Law of Conservation of Mass
• Evidence of a chemical change


  • Evolution of heat and light
  • Evolution of a gas
  • Formation of a precipitate
  • Production of mechanical energy
  • Production of electrical energy
• Law of Definite Composition/Proportion


  Elements combine in ratios of simple whole numbers to form a compound. Every sample of a given substance always contains the same proportion by mass of its constituent elements
• Law of Multiple Proportions


  When two elements combine to form two or more different compounds, if the amount of one element is constant, the masses of the other element in the different compounds are in ratios of small whole numbers
• Types of chemical reactions


  • Endothermic
  • Exothermic
• Endothermic reaction


  A reaction whereby energy is absorbed or taken in
• Endothermic reactions


  • Electroplating (coating of a metal on another material)
  • Electrolysis
• Exothermic reaction


  A reaction resulting in the release of energy
• Exothermic reactions


  • Production of flash bulbs
  • Batteries
  • Dynamites
  • Oxyacetylene torches
• Reaction mechanism


  The series of chemical steps involved in a chemical reaction
• Activation energy


  The minimum amount of energy needed to initiate a chemical reaction
• Heat of reaction


  The total amount of heat released or absorbed, usually measured in kJ/mol and given the symbol ΔH
• A negative value for a ΔH measurement is assigned to exothermic reactions while a positive ΔH is assigned to endothermic reactions
• The rate of a chemical reaction as well as the equilibrium between reactants and products is based on numerous factors, including temperature, concentration of reactants, pressure, and the presence of catalysts and/or inhibitors</b>
• Knowledge of Le Chatelier's Principle is important in understanding equilibrium situations
• Chemical equilibrium


  A state of balance between reactants and products
• Altering any of the experimental conditions forces the system to shift and establish a new equilibrium
• Pure substance


  Either an element or a compound, identified by its physical properties
• Elements are always present in the same ratio in a given compound. The properties of a compound are usually quite different from those of the elements of which it is composed
• Types of elements


  • Metals
  • Nonmetals
  • Metalloids
• Metals


  Hard and shiny elements that are good conductors of heat and electricity. They tend to lose electrons