Chap 10-11 sci

• When 2 objects are in contact, heat is transferred from the object of higher temperature to the object of lower temperature
• Temperature


  The measure of how hot an object is
• Thermometer


  Used to measure temperature
• Degree Celsius (°C)


  A common unit for temperature
• Kelvin (K)


  The SI unit for temperature
• The moter accident was caused by road damage
• The road surface cracked when water underneath it expanded as it turned to ice
• Expansion and contraction


  • May cause damage to structures that are constantly exposed to the environment
• Expansion in solids


  1. Solids expand when heated and contract when cooled

  2. Some solids expand very little such that we may not notice the expansion
• Glass cups for containing hot water should not be too thick
• When we pour boiling water too quickly into a cup made of thick glass, it sometimes cracks
• Reason for cracking


  The glass on the inside expands more quickly than the outside when heated
• The walls of glass containers for hot liquids are usually thin
• Expansion in liquids


  1. When a pot or kettle is filled to the brim with water, the water will spill out when it boils

  2. In general, most liquids expand when heated, and contract when cooled
• The liquid mercury in clinical thermometers responds quickly to heat
• The mercury level changes when the liquid is heated or cooled
• Reason for mercury level change


  The volume of the mercury changes
• Excessive expansion on very hot days can cause concrete to crack
• Tiles on pavement may also pop out
• Expansion gaps are laid between concrete slates and tiles to provide space for them to expand without any damage
• Telephone wires and electricity cables raised on poles may become taut and even snap in cold weather
• Telephone wires and electricity cables are strung loosely from pole to pole to allow for expansion and contraction
• Long bridges, such as the Benjamin Sheaves Bridge in Singapore, may expand up to a metre in hot weather
• Bridges and metal grinders on buildings have expansion gaps or are free and resting on rollers to allow the metal structures to expand without any damage on hot days
• If boiling water is poured into a thick glass, the glass is likely to crack due to the uneven expansion of the glass
• Most of the glassware found in the home and in the laboratory are made of a specialty of glass that is less likely to crack when hot liquids are poured into it
• Reason why specialty glassware is less likely to crack

  This type of glassware expands very little when heated
• Stalactite formation is an example of a chemical change
• Moulding of fruit is an example of a chemical change
• Acid "dissolving" a metal spoon is an example of a chemical change
• Physical change


  A change in which no new substances are formed
• Chemical change


  A change where substances called reactants are changed to produce new substances known as products
• When a chemical change occurs, a chemical reaction has taken place
• Reactants


  Substances that react with each other
• Products


  Substances that are formed
• Combustion


  A chemical reaction where a substance chemically combines with oxygen in the presence of heat, often giving out heat and light
• Thermal decomposition

  A process in which a substance breaks down into two or more simpler substances upon heating
• Oxidation


  When a substance gains oxygen, it undergoes a chemical change
• Acid


  A substance that dissolves in water to produce hydrogen ions (H+)
• Physical properties of acids

  • Have a sour taste
  • Some are corrosive
  • Conduct electricity when dissolved in water
  • Turn blue litmus paper red
  • pH less than 7