Ch 13: Solids and Liquids

1
Ch 13 Solids and Liquids

• Ch 13 begins with notes from Ch 3.6 and 3.7 on
  Energy, Temperature and Heat.
• We did not do these sections when in Ch 3 as the
  material is better discussed at the start of Ch
  13.

2
Ch 3.6 -- Energy, Temperature and Heat

• Energy is the capacity to do work
• chemical, mechanical, thermal, electrical,
  radiant, sound, nuclear
• Energy may affect matter
• e.g. raising or lowering its temperature will
  eventually cause a state change
• ex solid ? liquid? gas
• All physical changes and chemical changes involve
  energy changes

3

• Heat a flow of energy due to a temperature
  difference
• Heat flows from a region of higher temp to a
  region of lower temp until equilibrium is
  reached. (see fig 3.12, 3.13, 3.14 on page 67)
• Exothermic A process that results in the
  evolution of heat.
• Example when a match is struck, it releases
  energy as heat and light.
• Endothermic A process that absorbs energy.
• Example melting ice absorbs heat from the
  environment to form liquid water.

4
Ch 3.7 Calculating Energy Changes

• Calculate the quantity of energy required for
  various processes.
• Units
• calorie (cal) -- is the amount of energy needed
  to raise the temperature of one gram of water by
  1C
• A kilocalorie (kcal) 1000 cal energy needed
  to raise the temperature of 1000 g of water by
  1C
• In nutrition, a Calorie (capital C) is equal to
  one kcal (1000 cal)
• joule (J) the SI unit of energy
• 4.184 J 1 cal
• Converting J to cal (see example)

5
Energy and the Temperature of Matter

• The temperature increase of an object depends on
  the amount of heat added (Q).
• If the added heat energy is doubled, the
  temperature of the object will double.
• The temperature increase of an object also
  depends on its mass
• If the mass of the substance is doubled, it will
  take twice as much heat energy to raise the
  temperature the same amount.
• Specific Heat Capacity (s) the amount of
  energy required to raise the temperature of one
  gram of a substance by one degree Celsius. Units
  of s J/g oC
• Q s X m X ?T
• Q energy (heat) required
• s specific heat capacity of substance
• m mass of substance in grams
• ?T change in temperature in oC

6
Example 1 Converting calories to
joulesExample 2Calculate the amount of
heat energy (in joules) needed to raise the
temperature of 7.40 g of water from 29.0C to
46.0C
7
Example 3A 1.6 g sample of metal that appears
to be gold requires 5.8 J to raise the
temperature from 23C to 41C. Is the metal
pure gold?