Energy and Matter
Energy
• Energy has many forms. Heat is the
principal form of energy in chemistry.
• Units of energy –
• calorie, kilocalorie (Cal) [note capitalization
of “C” in Cal], Joules, kiloJoules.
• 1 kcal = 1000 cal
• 1 cal = 4.184 Joules
• 1 kcal = 4.184 kJ
Definitions / Thermal Properties
• Heat capacity is the amount of heat
required to raise the temperature of that
body 1 K. (note that this is the same
temperate change of 1 oC)
• Specific heat capacity of water is
cal
J
1.00
 4.184
gK
gK
Thermal properties
• Calorimetry – an object undergoing a
temperature change without a chemical
reaction or change of state absorbs or
discharges an amount of heat equal to its
heat capacity times the temperature
change.
• Heat exchange = (heat capacity) x
(temperature change)
Example
• How many joules are required to heat 100
g of copper (sp. Heat = 0.389 J/gK) from
10 oC to 100oC? The same quantity of
heat is added to 100 g of aluminum (sp.
Heat = 0.908 J/gK) at 10 oC. Which gets
hotter – copper or aluminum?
Example
• A steam boiler is made of steel and weighs
900 kg. The boiler contains 400 kg of
water. Assuming that 70% of the heat is
delivered to boiler and water, how much
heat is required to raise the temperature of
the whole from 10 oC to 100oC? Specific
heat capacity of steel is 0.11 kcal / kgK.
Example
• A 25.0 g sample of an alloy was heated to
100.0 oC and dropped into a beaker
containing 90 g of water at 25.32 oC. The
temperature of the water rose to a final
value of 27.18 oC. What is the specific
heat of the alloy?
Example
• Determine the resulting temperature when
150 g of ice at 0 oC is mixed with 300 g of
water at 50 oC. The heat of fusion of ice is
80 cal/g.
Example
• How much heat is required to convert 40 g
of ice (sp. Heat = 0.5 cal/gK) at -10 oC to
steam (sp. Heat = 0.5 cal/gK) at 120 oC?
The heat of fusion of ice is 80 cal/g. The
heat of vaporization of water is 540 cal/g.