Today’s lesson
• Demonstrate understanding of the term
thermal capacity
• Describe an experiment to measure the
specific heat capacity of a substance
• Recall and use the equation:
Energy = mass x specific heat capacity x
change in temperature
Imagine if……..
Two beakers containing different amounts of
water were heated by identical heaters for an
equal amount of time.
Imagine if……..
The beaker with less water gets hotter. WHY?
Imagine if……..
Two beakers, one containing water and one
containing kerosene (equal masses) were
heated by identical heaters for an equal amount
of time.
The beaker containing the kerosene would be
hotter! WHY?
Since the amount of heat energy supplied
is the same to both substances, it seems
that different substances require different
amounts of heat energy to cause the same
temperature rise.
Why are thermal capacities different?
• When a substance is heated, its internal
energy increases (potential and kinetic).
The stronger the force between the
particles in the substance, the more heat
energy goes into potential energy (and less
into kinetic), so the temperature rise is less
than in substances with little force between
particles. Obviously the more particles there
are too, the more heat energy can be
absorbed.
Specific heat capacity
Specific heat capacity is the amount of
energy needed to raise the temperature of
one kilogram of a substance by 1°C
Specific heat capacity of water = 4186 J/kg/°C
Specific heat capacity of kerosene = 2010 J/kg/°C
Specific heat capacity of mercury = 140 J/kg/°C
Calculations using S.H.C.
Energy absorbed = Mass x Specific Heat capacity x Temp rise
J
kg
J/kg/°C
E = mcΔT
°C
For example
0.5 kg of olive oil is heated until its temperature rises by
120 K. If the specific heat capacity of olive oil is 1970
J/kg/°C, how much heat energy was used?
Energy absorbed = Mass x Specific Heat capacity x Temp rise
Energy absorbed = 0.5 x 1970 x 120
Energy absorbed = 118200 J
An analogy: Water and wetness
“This analogy is
one of my ideas!”
Richard Feynmann – Nobel
prize winning Physicist,
lock-picker and bongo
player
Two towels – same size/mass
• You can add the same amount of water (heat), but the cheaper
towel will be “wetter” (temperature). They have different capacities
for absorbing water
Investigation time!
Let’s do an experiment to measure
specific heat capacities
thermometer
immersion heater
solid
block
Measuring SHCs
• Energy put IN to metal = voltage x current x time
• Energy = mass x specific heat capacity x temp rise
voltage x current x time = mass x specific heat capacity x temp rise
Specific heat capacity = (voltage x current x time)/(mass x temp rise)
Let’s try some
questions!