General Science

• Chemistry


  The study of matter, that is, anything that takes up space and has mass
• Mass


  A measure of the number of particles in an object
• Weight


  The influence of gravity on mass
• An object has the same mass on Earth as on the moon


  It will have a lower weight on the moon because there is less gravitational pull
• Density


  The mass per unit volume of a substance
• Units typically used to calculate density are grams (for mass) and milliliters (mL for volume)
• Cubic centimeters (cm3) is used instead of milliliters, and they are equivalent
• Substance


  Any variety of matter with identical properties and composition
• Substances are classified as


  • Elements
  • Compounds
• Elements


  Cannot be broken down chemically; made up of a particular atom, the basic building block of matter
• Compounds


  Can be broken down chemically; formed from the bonding of two or more elements
• Chemical reaction


  CH4 + 2O2 -> 2H2O + CO2
• The reaction shows the elements carbon, hydrogen, and oxygen in different compounds
• Mixture


  The result of the combination of elements and/or compounds
• Mixtures


  • The substances are not chemically combined (each substance retains its properties)
  • The ratios of substances can vary
  • The substances can be separated into the original elements and/or compounds
• Types of mixtures


  • Solution - transparent, particle sizes at molecule or ion level
  • Colloid
  • Suspension
• Homogeneous mixture


  Have only one phase, or have a uniform appearance throughout, and any portion of the sample has the same properties and composition
• Heterogeneous mixture


  Mixtures that are made up of more than one phase or of different parts and can be separated physically. The different components are visibly distinguishable from one another
• Homogeneous mixture


  • Homogenized milk
• Heterogeneous mixture


  • Mixture of sand in water
• Physical property


  Observable and measurable properties of substances, including phase, color, odor, density, boiling or melting point
• Chemical property


  Properties observed when a substance reacts with other substances. Chemical changes result in substances with different physical properties
• Chemical change


  • Iron (a gray, solid metal) reacts with oxygen gas (an odorless, colorless gas) to form iron oxide or rust (a solid that is orange-red in color)
• Potential energy


  Stored energy
• Gravitational energy


  The energy of position
• Forms of energy


  • Potential
  • Chemical energy
• Chemical energy


  The energy stored in the bonds of atoms and molecules
• Examples of stored chemical energy

  • Gasoline
  • Coal
• Nuclear energy


  The energy stored in the nucleus of an atom
• Example of nuclear energy

  • Uranium atom
• Stored mechanical energy


  Energy stored in compressed springs and stretched rubber bands
• Gravitational energy


  The energy of position, such as water in a reservoir behind a hydropower dam
• Water is released to spin the turbines


  It becomes kinetic energy
• Kinetic energy


  The energy of motion
• Exothermic reaction


  More energy is RELEASED than absorbed
• Endothermic reaction


  More energy is ABSORBED than released
• Radiant energy


  Electromagnetic energy such as X-rays and radio waves
• Example of radiant energy

  • Solar energy
• Thermal energy


  The internal energy of the vibrating molecules within substances
• Example of thermal energy


  • Geothermal energy